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How does the brain immediately know when one's thirst has been quenched?

How does the brain immediately know when one's thirst has been quenched?


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The question struck me the other day when I drank a glass of water. I understand that there are at least two conditions under which the brain signals thirst: extracellular thirst, when there's not enough fluid in the blood, and intracellular thirst, when the cells need more water to lower the concentration of osmolites.

However, it takes time for water to enter the bloodstream after it has been ingested, and it spends at least a little while in the stomach.

Why does the sensation of thirst disappear despite the water having not yet made it into my bloodstream?


There are two different aspects to or drivers of thirst, osmolality and hypovolemia, with plasma osmolality elevation being the more potent stimulus of thirst. As stated by @arboviral (and supported by his link), not a lot is known about the mechanisms of immediate thirst satiety. Much more is known about the mechanisms causing thirst, and the mechanisms of return to normal serum osmolality over 120-180 minutes after rehydration than those immediately satisfying it.

Most of the research on this is old (pre-2000). In one often-cited very small study 1, swallowing and esophageal reflexes (or as the authors termed it, “oropharyngeal metering”) had a significant effect on relief of thirst, that is,

the act of swallowing helps to regulate the volume of fluid ingested by providing an integrated signal proportional to the cumulative ingested volume.2

Study participants were all mildly dehydrated. One (control) group was allowed to drink ad lib. Another was allowed to drink ad lib but as they did so, the fluid was simultaneous extracted from the stomach by a nasogastric (ng) tube already in place. Interestingly, the difference in the amount of fluid ingested between these two groups (N.B. ad lib) was only 15% (the latter group drank a bit more.) The third group was given fluid by ng tube only.

The very act of swallowing fluid boluses induced satiety. However, plasma arginine vasopressin levels (involved in the regulation of fluid intake) dropped rapidly during the first 5 minutes of drinking in both ad lib groups, but not in those given fluids via ng tube, so it is not only mechanical receptors that are involved in quenching of thirst.

This confirmed an older study which demonstrated the importance of the rapid drop in plasma vasopressin in hydration before major changes in plasma osmolality occurred.3

Given the lack of extensive research and the relative immediacy of thirst suppression, The most likely explanation is a combination of sensory modalities and reflexes (mucosal wetness, temperature of rehydration fluid, mechanicoreceptors in the oropharynx, esophagus, etc.), and some rapid hormonal changes - e.g. in AVP - are responsible for limiting the amount we drink when thirsty.

1 Regulation of fluid intake in dehydrated humans: Role of oropharyngeal stimulation
2 Influence of age on thirst and fluid intake
3 Acute suppression of plasma vasopressin and thirst after drinking in hypernatremic humans


Satiety is divided into pre-absorption and post-absorption - the mechanism you're asking about is preabsorption satiety, which as you point out occurs long before the water can be absorbed into the bloodstream and appears to be remarkably accurate. The receptors and underlying mechanisms of pre-absorption satiety are not fully known but are thought likely to include moistening of the mucosa of the mouth and stretch receptors of the stomach and intestine.

I'll try to fill this out later but there's a longer description with diagrams on p309 of Schmidt & Thews (2013) "Human Physiology" (published by Springer).


I'd say the answer is easy.

  1. Since the whole body is one body all you need is the change of of water saturation in a part of you to determine / extrapolate how much water has been ingested.

  2. We all came from the water and are mostly made out of water. So it's not like water is a foreign substance and we needs special receptors in order to determine water content.

  3. We are water. And the system has evolved over time to be built in. I.e. the ones with a broken system have died of dehydration and anybody else survived.

  4. Of course you might be looking for one singular mechanism that says stop, that's enough. But it's a mixture of body temperature, what you have eaten, how much energy you have, etc. (water requires energy in order to be heated to your body temperature)

  5. That reminds me that apparently in hot regions you are supposed to drink tea or warm water because that allows you to drink more / be better hydrated. Based on that I'd guess it's just a temperature gradient? I.e. the water cools you down, and when it becomes too cold in your insides, you stop until you are hot enough again.


Food on the Brain

First up is our usual neuroscience news segment, and cognitive neuroscientist Duncan Astle has been looking into a paper asking whether man’s best friend can recognise faces in the same way that humans can.

Duncan - So they've recruited 40 participants - 20 humans, and 20 family dogs. For the humans their average age was 32, and 47% had a Master's degree or equivalent and 37% had a Bachelor's degree. For the dogs their average age was five and to date, none had yet completed any higher qualifications.

So all of the subjects were put in the fMRI scanner - the functional magnetic resonance imaging scanner. And they were shown videos with human faces or human backs of heads, and dog faces or dog backs of heads. So we've got a two by two design. Face versus back of head, and species - human versus dog. And the stimuli were really carefully controlled. So for example, the dogs and humans would never look directly at the camera and that's because apparently that can be triggering for dogs and can make them anxious or aggressive. So they had to think very carefully about how they delivered the stimuli. What they wanted to explore is whether or not both species are sensitive to faces versus backs of heads, and whether they discriminate the kind of species that it is.

The headline result is that in humans, there are lots of visual areas that are very sensitive to faces, but not particularly sensitive to species. Whereas in dogs, there were lots of visual areas that were highly sensitive to species. So those brain areas seem to distinguish another dog from a human being. But not to faces ie they don't seem to distinguish the front of the head from the back of the head.

Now, amongst their analyses, one that they ran was called an MVPA analysis or a multi-voxel pattern analysis. What it's doing is testing what information is being represented in different brain regions. So that if we read out the activity in that brain region, could we predict whether the person was currently looking at a face, a back of the head, a dog, or a human?

In the dogs they found that the left medial and right caudal supra sylvian gyrus showed really good decoding for species. So the dogs had brain areas that seem to be quite specialized for distinguishing dogs from humans, but there are no significant areas that seem to be specialised for distinguishing faces versus not faces i.e. backs of heads. Contrast that with the humans, so in one particular area, the right middle temporal gyrus, you can decode species, so they can distinguish humans from dogs. And then in loads of areas, including the fusiform gyrus, sometimes called the fusiform face area, you see selectivity for faces, so a classic face response. In essence, it seems to be that while both species can decode the species of the person they're looking at, only the humans seem to have this kind of selective face processing set of areas.

And a final analysis they did was called a representational dissimilarity analysis, a look at different brain areas to see how well it distinguishes all of the different videos that people were shown. And then they can test whether there are parts of a dog's brain that has a kind of profile across those video clips that's very similar to a part of the human's brain and vice versa. So they can see whether there are analogous regions in the dog that seem to have a similar kind of representational profile of faces and species as a human would have. And they find that they do get some analogous regions for species, but not for faces. Again, supporting the idea that dogs don't really recognise the human faces or the dog faces. And that is that.

Katie - So overall, is what the papers saying that dogs are really good at telling that's a human that's a dog, perhaps not individuals so well. Whereas humans are really good at going “that's Duncan, that's Helen, that's Katie”.

Duncan - Precisely. There are all sorts of explanations as to why that might be. So for example, most dog owners tell me that their dogs recognise them. But if the dogs can't really recognise human faces, then how can they recognise their owners? So my guess is that they're using other things. So it may be that for human beings because of the way that our visual systems work, because of our language systems, needing to look at lips and so on, it may be that we've become highly specialised for decoding faces and distinguishing one person's face from another. Whereas for dogs, someone's face is just one of many useful cues for distinguishing an individual from another. And because they're not really looking at lips for language, the face is perhaps less vital than it would be for a human.

So it's obviously a really interesting paper. I mean the very fact they've managed to get people's dogs into an fMRI scanner, I think is itself quite impressive. But behind, you know, kind of the novelty factor, they're asking a kind of interesting question, which is, where does this special processing for faces come from? At what point in our kind of evolutionary past does it develop or does it emerge? And, you know, we know that higher order primates have similar face processing areas to human beings, but it's obviously not ubiquitous to all mammals because the dogs don't show it. So the question is, when does it crop up and why? So it may be that for instance, humans and other primates have a kind of uniquely sort of social interaction and social structure, where being able to distinguish one person's face from another becomes a really useful tool that perhaps was not there previously for other kinds of mammals.

Now if you listened to the last few episodes of Naked Neuroscience, you’ll know we’ve been pondering the subject of play. And perceptual psychologist Helen Keyes’ paper of choice this month - asking whether playing with dolls can impact social development - fits rather nicely into that theme.

Helen - Engaging in pretend play is really helpful for a child's development. It helps them to develop both cognitively and socially. And this study was looking at the neuroscience of this. So what's happening in the brain when children are engaging in this pretend play?

So pretend play or what you might call, make believe play, typically involves using toys or dolls to act out a pretend scene. And so you might be really putting yourself in the position of your toys or taking the perspective of your dolls as you're playing with them. And this type of pretend play usually emerges around the age of two. It can happen alone, or it can happen with a play partner, but even when it's happening alone, there's a lot of evidence that this is still social in nature. So you're kind of imagining an audience in this type of play or you're taking the perspective of others in this type of play. So it is particularly interesting to us as psychologists to ask whether this type of perspective-taking in pretend play does help to develop childrens' social brains, essentially.

So the scientists in this study used fNIRS, which is functional near infrared spectroscopy. And that essentially measures blood flow in different regions of the brain. An increased blood flow would be a good indication that that part of the brain is particularly activated. And here the scientists used this fNIRS to measure blood flow in the brains of 33 children who are aged between four and eight, while they engaged in different types of play, Either open-ended creative play on a tablet - so this would be where you are cutting hair or building towns on the tablets, open-ended play - or if you're playing with dolls and kind of doll sets. Both of these activities were recorded when the children were playing alone with these activities or when they were playing socially. So the research assistant was engaging in this play with them.

And the researchers were particularly interested in the parts of the brain that are strongly involved with social cognition. So empathy and perspective taking, and the particular part of the brain they focused on was the posterior superior temporal sulcus. What they found, interestingly, was that there was no effect of the age of the child or of the gender of the child here. So the findings I'm going to talk to you about applied equally for boys and girls.

They found that the social regions of the brain were really activated during joint play in general. However, during solo play, when you're playing with a tablet that activation dropped off. So that social part of the brain wasn't engaged, but that activation remained for solo play when the children were playing with dolls. So it looks like imaginative play using dolls engages the social regions of your brain. These regions involved with empathy and perspective taking, even during solo play.

Katie - That's so interesting Helen, because anecdotally, I've sometimes heard, you know, of parents who have a little one and then are expecting another baby might say things like, "We'll get our little one a doll", in some way kind of to prepare them for having a sibling. Do you think this kind of speaks to that in any way?

Helen - I think it does speak to that. It seems that playing with dolls or engaging in this type of imaginative play is a way of rehearsing your social skills and in a way of, of really thinking, encouraging our children to think about other people and that perspective taking. So absolutely I would recommend it to be a good idea to ask your child to engage in this type of doll play, to develop them socially.

Katie - But do we actually know if it makes a difference? I guess it's one thing to say these areas of the brain are highlighted, but has anyone followed kids up and thought, "Ah, these kids are more empathetic adults", or anything like that?

Helen - Well, engaging with this type of pretend play, yes, we do know that it's good for different areas of the brain. In general, engaging in pretend play is good for your cognitive skills and your social skills. So that's quite well established. What was interesting about this study, was it was showing that even in the absence of a playmate or that direct social stimulation, at a neural level we can see that engaging in imaginative play with dolls is, you know, recruiting those areas. In a way, making those areas practice your social skills. So yeah, we do know that engaging in pretend play is good for your social skills, but this is such a direct neural demonstration of that. It's just really strong evidence.

Katie - Do you think the tablet is a good comparison? I was just wondering about, you know, what, if you just give a kid some blocks or a stick or, or nothing, and just ask them to make up a game? Would that be more work for the brain?

Helen - The reason they didn't do that is if you give a child some blocks or some sticks, they will often engage in the type of pretend play that we would engage with when we're using dolls. They often won't, sometimes they will just stack the bricks or make rules for a game for themselves, but they really wanted to disentangle those social elements here by just giving a child a tablet and asking them to engage in a creative free play, not a rule based game, but it wasn't a social game.

The other point I wanted to make was that this study was funded by Mattel who make Barbie. So while I'm very confident looking at the research methods and looking at the researchers involved in this study, that it was, you know, a proper legit study, it is important to say that it was funded by the makers of Barbie.

Duncan - fNIRS is great in that it's portable. The kids can play. We haven't got to slide them in a scanner. But also one of the challenges is that you don't necessarily get the same coverage. So one possibility is that whilst the tablets seem to be less engaging social areas, it may be that what kids can do on them is more cognitively demanding in other ways than playing with a doll. So for example, if they're building something on Minecraft on the screen, it may be that they're engaged in all sorts of other areas to a greater extent than playing with a doll. Different toys for different types of play, yielding different types of benefit. Do you think that's possible?

Helen - Absolutely. I think that is certainly the case. If we were asking a child to engage in rule-based play, we would almost certainly see frontal areas, the prefrontal cortex, recruited, much more than during doll play. So absolutely I would recommend that we should be encouraging our children into all these different types of play. So not, you know, doll play alone might be great for social skills, but not so great for cognitive skills and vice versa. I think what it really tells us, when we put all this research together, is it's a really bad idea to have children just playing with one type of stimulus or one type of game all the time.


What Is Thirst? A Neuroscientist Explains What’s Really Getting Turned On in Your Brain

“Thirst” has been used to describe more than dehydration for centuries and originally conveyed a deep sense of religious desire. But a combination of smartphones, social media, dating apps, hip-hop, attention-seeking millennials and butt selfies all helped thirst reach its godless potential as the most dramatic and transparent expression of horniness to date. Brands are thirsty. Memes are thirsty . And politicians? They’re thirsty as hell . Thirst is everywhere and has become a more effective way to bring up sex than water.

Scientifically, thirst actually marks the earliest stages of arousal: The brain begins to rally resources to focus on sex and the anticipation of having it. It’s also one of the most well-documented areas of sexual research, explains psychophysiologist and neuroscientist Nicole Prause . “We know very little about reward receipt in sex,” she says. “Almost everything that’s been studied focused on reward anticipation.” In other words, most of what we know about the science of sex comes from the science of thirst.

Following a decade of research at the Sexual Psychophysiology and Affective Neuroscience Laboratory , Prause started the sexual biotechnology company Liberos in 2015, where she continues to discover more about our thirsty brains. Here’s what she offers us to drink on the topic…

Thirsty People Need More Oxygen

The earliest stages of sexual arousal don’t occur in any one distinct area of the brain, but many such areas — including the amygdala , anterior cingulate , ventral striatum and hypothalamus , each of which requires more oxygen during this time. And, like any good athlete, the thirstier a person gets, the more oxygen they need. “As someone becomes more sexually aroused, they increase their use of oxygen,” Prause says.

Thirst Might Be an Emotion

Allow Prause to (once again) explain: “The brain areas that become active during sexual arousal are very similar to the brain areas that become active during any pleasant emotional experience, which has led some scientists to call sexual arousal another emotion.”

Basically: You’re not horny, you’re just emotional.

Thirst Can Lead to Bad Decisions

This might be obvious, but it’s also biology. That is, w hile in a state of horniness, increased blood and oxygen flow to parts of the brain linked with touch, emotion and pleasure. This directs blood and oxygen away from the frontal lobe, which is needed for important cognitive skills like memory, problem-solving, judgment and self-control.

Prause suspects that the reason sexual arousal appears to impair decision-making is — anecdotally — because the brain is working so hard to focus on anticipated sexual stimuli that there’s little bandwidth left for anything else. Thus, she adds, “Changes in how we make decisions while sexually aroused are likely mostly attributable to not having our usual resources of attention and memory available to us.”

Thirst Depends on Where Your Next ‘Drink’ Is Coming From

Horny people typically fall into two camps, neurologically speaking: 1) Those who know their thirst will be satisfied in the near future and 2) everyone else who has to get back to work.

In a recent study , Prause found that when men and women anticipate sex and then receive genital stimulation with a vibrator (which studies show also effectively stimulate men), their alpha waves become suppressed. Since alpha waves are at their highest when people are awake but not focused, like when watching TV, alpha-wave suppression is used as an indicator of increased attention and engagement. Simply, when people become thirsty, their alpha waves went down, but only if they received stimulation. When participants anticipated sex without receiving vibrator stimulation, their alpha waves didn’t decrease, meaning they were less preoccupied by sex.

Or the TLDR version: When people know their thirst won’t be quenched, their brains don’t rev up to the same extent, and most are cognitively capable of pivoting their attention.

Thirstiness Is Probably Genetic

A person’s sex drive depends on how a person’s ventral striatum, or reward system in the brain, responds to dopamine. People with high sex drives tend to have ventral striata that are more reactive to dopamine, whereas people who have low sex drives have reward systems that respond less to pleasure across the board. For instance, someone who gets excited about roller coasters would be more prone to promiscuity than someone who hates Six Flags. This is why antidepressants, clinical depression and even Parkinson’s medications can mess with horniness: They affect dopamine production and responses.

Barring medication side effects, reward sensitivity and dopamine depend less on lifestyle factors like masturbation or porn consumption and more on a person’s parents. “Both of those brain responses have been shown to be somewhat heritable,” Prause says.

If you’re thirsty, then, imagine how your mom must feel.

Thirsty Doesn’t Always Mean DTF

Everyone’s sex drive comes with a gas pedal and a break, or what scientists call “reward motivation” and “inhibitory tone.” Reward motivation is determined by genetics, but inhibitory tone, or how much the brain inhibits dopamine, is based on more external factors — namely, if the situation is safe enough to satiate your thirst. Although a person’s ability to respond to threats becomes diminished during the later stages of sexual arousal approaching orgasm, the parts of the brain that detect and signal potential threats, the amygdala and hypothalamus , are still active during the earlier stages. Which means that horniness can come to a screeching halt if something doesn’t seem right.

“Someone not wanting to have sex doesn’t mean they necessarily have a low sex drive, they may just need more safety signals or change in social situation to reduce the inhibition on their preferred sexual desires,” Prause explains, adding that some people may appear to get more turned on when frightened, but that’s normally limited to superficial fear (e.g., horror movies or BDSM), when a person knows they’re not in actual danger. “Many emotion scientists wouldn’t call this fear, but more likely excitement,” Prause continues.

As frustrating as this can be in the moment, the good news is that our brains are wired to protect us even when we’re horny. So you might do a few dumb things, but you aren’t going to die of thirst.

Lauren Vinopal

Lauren Vinopal is a writer and stand-up comedian based out of New York City, who writes mostly about health, science and men. She is the host of the Mid Riff Comedy Show in Brooklyn, a frequent podcast guest all over, and lives the life of a teen who looks like they haven’t slept in years.


Water Or A Sports Drink? These Brain Cells May Decide Which One We Crave

Researchers appear to have shown how the brain creates two different kinds of thirst.

The process involves two types of brain cells, one that responds to a decline in fluid in our bodies while the other monitors levels of salt and other minerals, a team reports in the journal Nature.

Together, these specialized thirst cells seem to determine whether animals and people crave pure water or something like a sports drink, which contains salt and other minerals.

"Our brain can detect these two distinct stimuli with different cell types," says Yuki Oka, a professor of biology at Caltech and the study's lead author.

The finding appears to help answer "this question that we've been trying to ask for decades and decades and decades," says Sean Stocker, a professor at the University of Pittsburgh who studies water and salt balance in the body. Stocker was not involved in the study.

Oka's research is part of an effort to understand the brain biology underlying behavior that's seen in people and many animals.

For example, people who've just finished a long, sweaty workout often experience a special kind of thirst.

"Pure water doesn't do it, right? It's not enough," Oka says. "You need water and salt to recover. And we can easily imagine that under such condition we crave [a] sport drink."

Sports drinks like Gatorade generally include a mix of salt and sugar, as well as water.

To understand what triggers this type of thirst, Oka's team studied cells in two regions of mouse brains. Both regions are known to contain neurons involved in the sensation of thirst.

The team induced two kinds of thirst in the mice. One was caused by a simple lack of fluid in the body. The other simulated the loss of fluid and minerals that occurs during a sweaty workout.

And each type of thirst appeared to produce a response from a different type of cell.

To confirm that these cells are truly linked to drinking behavior, Oka's team did an experiment that gave mice access to two bottles. One contained pure water and the other a mixture of water and minerals, including salt.

Then the team used a technique called optogenetics to stimulate each type of thirst cell in the mice.

When they stimulated the water-only thirst cells, the mice immediately went to the bottle of pure water and began "drinking vigorously," Oka says.

But when the team stimulated the cells that responded to salt levels, the mice began drinking a combination of pure water and salty water. In essence, they reached for the mouse version of a sports drink.

The team focused on how cells in the two brain regions affected thirst. But scientists say these and other cell types are probably involved in regulating a wide range of bodily functions and behaviors.

"Is it only thirst-related or does it also affect heart rate or blood pressure, or temperature regulation," says Claire Gizowsky, a postdoctoral scholar at the University of California, San Francisco. "These are all interconnected," she says.

The link to blood pressure is highly likely, Stocker says. Decades of research has shown how levels of salt and fluid in the body can change a person's blood pressure.

Stocker's own research has found links between brain cells involved in thirst and those involved in blood pressure. And he says it's likely that many blood pressure drugs act on the same brain areas that regulate fluid and salt intake.

Understanding how thirst cells work in the brain could also help certain sick people and athletes.

"Fluid balance is one of the top ten factors that causes you to be admitted into a hospital when you show up to the ER," she says. Some of those trips might be avoided if scientists could develop a sensor that worked the same way the brain does to monitor fluid and salt levels.

Also, Gizowsky says: "This would be super helpful for athletes to know how much Gatorade they're supposed to drink to have optimal performance."

Gizowsky thinks the next frontier in thirst science is figuring out how the brain anticipates the need for fluid or salt.

"Sometimes you drink and you don't even realize that you're drinking or that you're even thirsty because your body is just doing these things without you knowing," she says. That's probably to protect you from "the consequences of not drinking water and not being hydrated properly" later on. [Copyright 2020 NPR]


How Can You Quench Your Thirst?

The answer depends on what is making you so thirsty. Drinking more water is a good place to start. But if you can’t satisfy your craving for it, talk with your doctor.

Whatever the cause, don’t just live with it. Most of the conditions that cause thirst are treatable.

Sources

Popkin, B. Nutrition Reviews, August 2010.

CDC: “Water: Meeting your Daily Fluid Needs,” “Water & Nutrition.”

American Dental Association: “Dry Mouth.”

Cleveland Clinic: “Avoiding Dehydration, Proper Hydration.”

American Diabetes Association: “Diabetes Symptoms.”

UCSF Medical Center: “Diabetes Insipidus.”

Johns Hopkins Medicine: “Dehydration and Heat Stroke,” “Diabetes Insipidus.”

National Institutes of Health: “Your Guide to Anemia.”

Sjogren’s Syndrome Foundation: “Dry mouth: A Hallmark Symptom of Sjogren’s Syndrome.”


Learning How Little We Know About the Brain

Research on the brain is surging. The United States and the European Union have launched new programs to better understand the brain. Scientists are mapping parts of mouse, fly and human brains at different levels of magnification. Technology for recording brain activity has been improving at a revolutionary pace.

The National Institutes of Health, which already spends $4.5 billion a year on brain research, consulted the top neuroscientists in the country to frame its role in an initiative announced by President Obama last year to concentrate on developing a fundamental understanding of the brain.

Scientists have puzzled out profoundly important insights about how the brain works, like the way the mammalian brain navigates and remembers places, work that won the 2014 Nobel Prize in Physiology or Medicine for a British-American and two Norwegians.

Yet the growing body of data — maps, atlases and so-called connectomes that show linkages between cells and regions of the brain — represents a paradox of progress, with the advances also highlighting great gaps in understanding.

So many large and small questions remain unanswered. How is information encoded and transferred from cell to cell or from network to network of cells? Science found a genetic code but there is no brain-wide neural code no electrical or chemical alphabet exists that can be recombined to say “red” or “fear” or “wink” or “run.” And no one knows whether information is encoded differently in various parts of the brain.

Brain scientists may speculate on a grand scale, but they work on a small scale. Sebastian Seung at Princeton, author of “Connectome: How the Brain’s Wiring Makes Us Who We Are,” speaks in sweeping terms of how identity, personality, memory — all the things that define a human being — grow out of the way brain cells and regions are connected to each other. But in the lab, his most recent work involves the connections and structure of motion-detecting neurons in the retinas of mice.

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Larry Abbott, 64, a former theoretical physicist who is now co-director, with Kenneth Miller, of the Center for Theoretical Neuroscience at Columbia University, is one of the field’s most prominent theorists, and the person whose name invariably comes up when discussions turn to brain theory.

Edvard Moser of the Norwegian University of Science and Technology, one of this year’s Nobel winners, described him as a “pioneer of computational neuroscience.” Mr. Abbott brought the mathematical skills of a physicist to the field, but he is able to plunge right into the difficulties of dealing with actual brain experiments, said Cori Bargmann of Rockefeller University, who helped lead the N.I.H. committee that set a plan for future neuroscience research.

“Larry is willing to deal with the messiness of real neuroscience data, and work with those limitations,” she said. “Theory is beautiful and internally consistent. Biology, not so much.” And, she added, he has helped lead a whole generation of theorists in that direction, which is of great value for neuroscience.

Dr. Abbott is unusual among his peers because he switched from physics to neuroscience later in his career. In the late 1980s, he was a full professor of physics at Brandeis University, where he also received his Ph.D. But at the time, a project to build the largest particle accelerator in the world in Texas was foundering, and he could see a long drought ahead in terms of advances in the field.

He was already considering a career switch when he stopped by the lab of a Brandeis colleague, Eve Marder, who was then, and still is, drawing secrets from a small network of neurons that controls a muscle in crabs.

She was not in her lab when Dr. Abbott came calling, but one of her graduate students showed him equipment that was recording the electrical activity of neurons and translating it into clicks that could be heard over speakers each time a cell fired, or spiked. “You know what?” he said recently in his office at Columbia, “We wouldn’t be having this conversation if they didn’t have that audio monitor on. It was the sound of those spikes that entranced me.”

Decoding the Brain’s Math

“I remember I walked out of the door and I kind of leaned up against the wall, in terror, saying, ‘I’m going to switch,’ ” he added. “I just knew that something had clicked in me. I’m going to switch fields, and I’m dead, because nobody knows me. I don’t know anything.”

Dr. Marder served as his guide to the new field, telling him what to read and answering his many questions. He was immediately accepted both in her lab and by other experimentalists, she said, “because he’s both wicked smart and humble.”

“He did something that was astonishing,” Dr. Marder said. “Six months in, he actually understood what people knew and what they didn’t know.”

Dr. Abbott recalled that it took a while for them to develop a productive collaboration. “Eve and I talked for a year and then finally started to understand each other,” he said.

Together, they invented something called the dynamic clamp technique, a way to link brain cells to a computer to manipulate their activity and test ideas about how cells and networks of cells work.

A decade ago, he moved from Brandeis to Columbia, which now has one of the biggest groups of theoretical neuroscientists in the world, he says, and which has a new university-wide focus on integrating brain science with other disciplines.

The university is now finishing the Jerome L. Greene Science Center, which will be home to the Mortimer B. Zuckerman Mind Brain Behavior Institute. The center for theoretical neuroscience will move to the new building.

Dr. Abbott collaborates with scientists at Columbia and elsewhere, trying to build computer models of how the brain might work. Single neurons, he said, are fairly well understood, as are small circuits of neurons.

The question now on his mind, and that of many neuroscientists, is how larger groups, thousands of neurons, work together — whether to produce an action, like reaching for a cup, or to perceive something, like a flower.

There are ways to record the electrical activity of neurons in a brain, and those methods are improving fast. But, he said, “If I give you a picture of a thousand neurons firing, it’s not going to tell you anything.”

Computer analysis helps to reduce and simplify such a picture but, he says, the goal is to discover the physiological mechanism in the data.

For example, he asks why does one pattern of neurons firing “make you jump off the couch and run out the door and others make you just sit there and do nothing?” It could be, Dr. Abbott says, that simultaneous firing of all the neurons causes you to take action. Or it could be that it is the number of neurons firing that prompts an action.

His tools are computers and equations, but he collaborates on all kinds of experimental work on neuroscientific problems in animals and humans. Some of his recent work was with Nate Sawtell, a fellow Columbia researcher, and Ann Kennedy a graduate student at the time in Dr. Sawtell’s lab, now doing post-doctoral research at Caltech. Their subject was the weakly electric fish.

Unlike electric eels and other fish that use shocks to stun prey, this fish generates a weak electric field to help it navigate and to locate insects and other prey. Over the years, researchers, notably Curtis Bell at the Oregon Health and Science University, have designed experiments to understand, up to a point, how its brain and electric-sensing organs work.

Dr. Abbott joined with Dr. Kennedy and Dr. Sawtell, the senior author on the paper that grew out of this work, and others in the lab to take this understanding a step further. The fish has two sensing systems. One is passive, picking up electric fields of other fish or prey. Another is active, sending out a pulse, for communication or as an electrical version of sonar. They knew the fish was able to cancel out its own pulse of electricity by creating what he called a “negative image.”

They wired the brain of a weakly electric fish and — through a combination of testing and developing mathematical models — found that a surprising group of neurons, called unipolar brush cells, were sending out a delayed copy of the command that another part of the brain was sending to its electric organ. The delayed signal went straight to the passive sensing system to cancel out the information from the electric pulse.

“The brain has to compute what’s self-generated versus what’s external,” said Dr. Sawtell.

This may not sound like a grand advance, but, Dr. Abbott said, “I think it’s pretty deep,” adding that it helps illuminate how a creature begins to draw a distinction between itself and the world. It is the very beginning of how a brain sorts a flood of data coming in from the outside world, and gives it meaning.

That is part of the brain’s job, after all — to build an image of the world from photons and electrons, light and dark, molecules and motion, and to connect it with what the fish, or the person, remembers, needs and wants.

“We’ve looked at the nervous system from the two ends in,” Dr. Abbott said, meaning sensations that flow into the brain and actions that are initiated there. “Somewhere in the middle is really intelligence, right? That’s where the action is.”

In the brain, somehow, stored memories and desires like hunger or thirst are added to information about the world, and actions are the result. This is the case for all sorts of animals, not just humans. It is thinking, at the most basic level.

“And we have the tools to look there,” he said. “Whether we have the intelligence to figure it out, I view that, at least in part, as a theory problem.”


Comment on: “The Utility of Thirst as a Measure of Hydration Status Following Exercise-Induced Dehydration”

1.5 L of fluid for each kilogram of body weight lost.” According to this recommendation, and within the context of Adams et al.’s [1] example, it follows that participants of their study would have had to consume a whopping 3.5 L of fluid within the half-time period to restore fluid balance. Or, alternatively, taking Adams et al.’s [1] recommendation at face value, it is rather 4.6 L of water that athletes should have consumed, of which one half would serve to replace fluid losses and the other to compensate for the upcoming sweat losses of the second half of the game. Independent of the strategy used, it is highly probable that such amounts of fluid consumed within this short period of time could lead to subsequent stomach bloating and pain, nausea, vomiting, an urge to urinate, or discomfort which, in addition to being detrimental for health, may lead to performance impairment [15,16] or a need to exit from the game field.


Water Or A Sports Drink? These Brain Cells May Decide Which One We Crave

Researchers appear to have shown how the brain creates two different kinds of thirst.

The process involves two types of brain cells, one that responds to a decline in fluid in our bodies, while the other monitors levels of salt and other minerals, a team reports in the journal Nature.

Together, these specialized thirst cells seem to determine whether animals and people crave pure water or something like a sports drink, which contains salt and other minerals.

"Our brain can detect these two distinct stimuli with different cell types," says Yuki Oka, a professor of biology at Caltech and the study's lead author.

The finding appears to help answer "this question that we've been trying to ask for decades and decades and decades," says Sean Stocker, a professor at the University of Pittsburgh who studies water and salt balance in the body. Stocker was not involved in the study.

Oka's research is part of an effort to understand the brain biology underlying behavior that's seen in people and many animals.

For example, people who've just finished a long, sweaty workout often experience a special kind of thirst.

"Pure water doesn't do it, right? It's not enough," Oka says. "You need water and salt to recover. And we can easily imagine that under such condition, we crave [a] sport drink."

Sports drinks like Gatorade generally include a mix of salt and sugar, as well as water.

To understand what triggers this type of thirst, Oka's team studied cells in two regions of mouse brains. Both regions are known to contain neurons involved in the sensation of thirst.

The team induced two kinds of thirst in the mice. One was caused by a simple lack of fluid in the body. The other simulated the loss of fluid and minerals that occurs during a sweaty workout.

And each type of thirst appeared to produce a response from a different type of cell.

To confirm that these cells are truly linked to drinking behavior, Oka's team did an experiment that gave mice access to two bottles. One contained pure water and the other a mixture of water and minerals, including salt.

Then the team used a technique called optogenetics to stimulate each type of thirst cell in the mice.

When they stimulated the water-only thirst cells, the mice immediately went to the bottle of pure water and began "drinking vigorously," Oka says.

But when the team stimulated the cells that responded to salt levels, the mice began drinking a combination of pure water and salty water. In essence, they reached for the mouse version of a sports drink.

The team focused on how cells in the two brain regions affect thirst. But scientists say these and other cell types are probably involved in regulating a wide range of bodily functions and behaviors.

"Is it only thirst related, or does it also affect heart rate or blood pressure or temperature regulation?" says Claire Gizowski, a postdoctoral scholar at the University of California, San Francisco. "These are all interconnected," she says.

The link to blood pressure is highly likely, Stocker says. Decades of research have shown how levels of salt and fluid in the body can change a person's blood pressure.

Stocker's own research has found links between brain cells involved in thirst and those involved in blood pressure. And he says it's likely that many blood pressure drugs act on the same brain areas that regulate fluid and salt intake.

Understanding how thirst cells work in the brain could also help certain sick people and athletes.

"Fluid balance is one of the top 10 factors that causes you to be admitted into a hospital when you show up to the ER," Gizowski says. Some of those trips might be avoided if scientists could develop a sensor that worked the same way the brain does to monitor fluid and salt levels.

Also, Gizowski says: "This would be super-helpful for athletes to know how much Gatorade they're supposed to drink to have optimal performance."

Gizowski thinks the next frontier in thirst science is figuring out how the brain anticipates the need for fluid or salt.

"Sometimes you drink and you don't even realize that you're drinking or that you're even thirsty because your body is just doing these things without you knowing," she says. That's probably to protect you from "the consequences of not drinking water and not being hydrated properly" later on.

An earlier version of this story misspelled Claire Gizowski's last name as Gizowsky.

And now we have an update for you on the science of thirst. NPR's Jon Hamilton reports on special brain cells that appear to tell us when we want just plain water and when we might crave one of those fancy sports drinks.

JON HAMILTON, BYLINE: When you're sweating through a long workout, your body loses minerals as well as fluid. And Yuki Oka of Caltech says that produces a special kind of thirst.

YUKI OKA: Pure water doesn't do it. It's not enough. You need water and salt to recover. And we can easily imagine that under such condition, we crave for sports drink.

HAMILTON: Which is basically a mix of water, salt and sugar - Oka wanted to know what triggers this craving. So he and a team studied the cells in two regions of mouse brains.

OKA: So those regions contain neurons that drive thirst.

HAMILTON: Oka's team induced two kinds of thirst in the mice. One was caused by a simple lack of fluid in the body. The other stimulated the loss of fluid and minerals that occurs during a sweaty workout. And Oka says each type of thirst produced a different response in the brain.

OKA: Our brain can detect these two distinct stimuli with different cell types.

HAMILTON: One type of brain cell was responding to a need for water alone. The other detected a need for salt as well. To confirm the finding, Oka's team did an experiment with mice.

OKA: We presented two bottles, one with pure water, another one with water plus minerals.

HAMILTON: Then the team used a technique called optogenetics to stimulate each type of thirst cell in the mice. Oka says when they stimulated the water-only thirst cells.

OKA: Then animal immediately went to water and it started drinking vigorously.

HAMILTON: But only from the bottle of pure water - next, the team stimulated the thirst cells that respond to salt levels.

OKA: Now mice start drinking both pure water and minerals.

HAMILTON: The mouse version of reaching for a sports drink - Sean Stocker of the University of Pittsburgh says the experiments, which appear in the journal Nature, represent a scientific tour de force.

SEAN STOCKER: They bring the most cutting-edge techniques to bear on this question that we've been trying to ask for decades and decades and decades.

HAMILTON: Stocker says the question goes beyond thirst. The cells in these brain regions appear to be involved in a wide range of bodily functions.

STOCKER: This study has implications not simply for fluid intake but clearly for other things such as blood pressure regulation.

HAMILTON: Too much salt and fluid in the body can cause high blood pressure, and Stocker says many of today's blood pressure drugs appear to be affecting cells in the same areas of the brain that regulate thirst. Claire Gizowski is a researcher at the University of California, San Francisco. She says this new understanding of how thirst works could lead to better health.

CLAIRE GIZOWSKI: Fluid balance is one of the top 10 factors that cause you to be admitted into a hospital when you show up to the ER.

HAMILTON: Some of those trips might be avoided if vulnerable people had some sort of sensor that worked the same way the brain does to monitor fluid and salt levels. Also, Gizowski says.

GIZOWSKI: This would be super-helpful for athletes to, you know, know how much Gatorade they're supposed to drink to, like, have optimal performance.

HAMILTON: Gizowski thinks the next frontier in thirst science is figuring out how the brain anticipates the need for fluid or salt.

GIZOWSKI: Sometimes, you drink, and you don't even realize that you're drinking or that you're even thirsty because your body is just doing these things without you knowing.

HAMILTON: She says that's probably to protect you from a fluid imbalance later on.


Your Brain Doesn't Work the Way You Think It Does

At the very beginning of her new book Seven and a Half Lessons About the Brain, psychology professor Lisa Feldman Barrett writes that each chapter will present “a few compelling scientific nuggets about your brain and considers what they might reveal about human nature.” Though it’s an accurate description of what follows, it dramatically undersells the degree to which each lesson will enlighten and unsettle you. It’s like lifting up the hood of a car to see an engine, except that the car is you and you find an engine that doesn’t work at all like you thought it did.

For instance, consider the fourth lesson, You Brain Predicts (Almost) Everything You Do. “Neuroscientists like to say that your day-to-day experience is a carefully controlled hallucination, constrained by the world and your body but ultimately constructed by your brain,” writes Dr. Barrett, who is a University Distinguished Professor at Northeastern and who has research appointments at Harvard Medical School and Massachusetts General Hospital. “It’s an everyday kind of hallucination that creates all of your experiences and guides all your actions. It’s the normal way that your brain gives meaning to the sensory inputs from your body and from the world (called “sense data”), and you’re almost always unaware that it’s happening.”

People tend to feel like we’re reacting to what’s actually happening in the world. But what’s really happening is that your brain is drawing on your deep backlog of experience and memory, constructing what it believes to be your reality, cross-referencing it with incoming sense data from your heart, lungs, metabolism, immune system, as well as the surrounding world, and adjusting as needed. In other words, in a process that even Dr. Barrett admits “defies common sense,” you’re almost always acting on the predictions that your brain is making about what’s going to happen next, not reacting to experience as it unfolds. (Michael Pollan details the same neurological process in his book How to Change Your Mind.)

“Predictions transform flashes of light into the objects you see. They turn changes in air pressure into recognizable sounds, and traces of chemicals into smells and tastes. Predictions let you read the squiggles on this page and understand them as letters and words and ideas,” Barrett writes. “They’re also the reason why it feels unsatisfying when a sentence is missing its final.”

In her first book, How Emotions Are Made, Dr. Barrett cites research that suggests something similar happens with emotion. We experience things like anger or anxiety as feelings caused by outside events. But really, as Dr. Barrett says, “Emotions don’t happen to you—they are made by your brain as you need them.” That may sound like splitting hairs, but the consequences are quite profound: The more you know about emotions, the more precisely your brain can construct them, so you will feel and act in ways that are very specific to the situation. We talk a lot about “handling” emotions after they emerge (this is called emotion regulation), but understanding emotions as something you construct allows you to influence how they arise in the first place.

Of course, this upends notions of how we experience reality and leads to some interesting questions. Why does this happen? If we construct the reality around us, including our emotions, does that mean we can change how we feel? What should we do with the anxiety and stress brought on by coronavirus? If our actions are dependent on past experience, do we control what we do? How do we think about responsibility—say, in the renewed conversation around police violence—in a world like that? How can we use these seven and a half lessons to better exist in the world? GQ spoke to Dr. Barrett to ask these questions and more.

GQ: Your first lesson, which is actually a half lesson, is that the brain is not for thinking. So then: what is the brain for?

Lisa Feldman Barrett: The brain's most important job is not thinking or seeing or feeling or doing any of the things that we think of as being important for being human. Its main job is running a budget for your body—to keep you alive, to keep you healthy. So every thought you have, every emotion you feel, every action you take is ultimately in the service of regulating your body. We don’t experience mental life this way, but this is what is happening under the hood.

The technical term for body budgeting is allostasis. It basically means that your brain’s job is to anticipate the needs of your body and meet those needs before they arrive. Budgeting resources like glucose, oxygen, salt, and all of the nutrients that your body needs so that you can do your most important job from an evolutionary standpoint: pass your genes on to the next generation.

There are limited resources [in your body] and every action that you take—every movement that you make, every new thing that you learn—costs something. And so every time your brain prepares to move your body or to learn something new, your brain is asking itself, figuratively, is this a good investment? Is it worth it?

This is one of the most amazing, and unsettling, revelations in the book, this idea that the brain is a prediction machine. Instead of passively observing reality—in what we think of as a stimulus-response pattern—it's actually constructing our reality?

We can use a baseball example. The batter walks up to the plate. He takes his stance with the bat. A major league pitcher throws at a speed of 80 to 100 mph, giving the batter between 400 and 500 milliseconds to react. This is not enough time to see a ball, then decide to swing the bat, plan the action, and execute it. But a brain that works by prediction is fast enough to make baseball possible as a game.

Here’s what’s really happening: based on all the information that the batter has about the situation, his brain is automatically computing the swing, making a prediction about, in a moment's time, where will the ball be. And so in the blink of an eye, his brain predicts the action, and then predicts his sensations. Figuratively speaking, his brain predicts: “What will I do in a moment from now? And the last time I acted this way in this situation, what did I see ? What will I feel in my joints? When the bat strikes the ball, what will I hear?” His brain is automatically changing the firing of its own neurons to anticipate the sensory changes that will result from the crack of the ball against the bat.

And so what happens? Information is coming in through his eyes and his ears and the rest of his sense organs. If the new information matches the prediction, then his motor response is completed, he swings the bat as planned and probably hits the ball. If there's a difference, though, if his brain has not predicted something, say there's a gust of wind or something happens with one of his tendons, then his brain may take in that new information and automatically adjust its prediction. But that adjustment will take long enough that he could miss the ball.

Predicting and correcting is a much more efficient way to run a system than reacting all the time. So what your brain is doing all the time is making these guesses, and then comparing them to sense data from your body and from the world that is continually arriving, as a way of reducing uncertainty, which, it turns out, is the metabolically efficient thing to do.

The example that got me in the book was the fact that it takes 20 minutes for water to reach your bloodstream, so when you drink a glass of water and feel like your thirst is immediately quenched, that’s not a biological reality, but a kind of a neurological trick.

Here's another one that I just learned. You know how when it’s just starting to rain, and you might feel one drop of water on your skin, and you can tell it’s going to start to rain? Well, you have no wetness sensors in your skin. So how is it that you feel those drops of water? Your skin has touch sensors and temperature sensors, and your brain is doing this internal calculus, integrating the information about touch with the information about temperature to construct a prediction of water on your skin. So when you feel wetness under your underarms or you feel dampness on your skin for any reason, it’s basically a construction of your brain taking two sources of information and combining them.

Every single thing that you do, and every single thing that you feel and think—basically everything you experience—is some combination of what's going on inside your brain and what's going on outside your skull. Your brain doesn't know for sure what's going on in your body. It’s only receiving sense data. That sense data is the effect of some set of causes that are going on in your body. But your brain doesn't know what the causes are. It has to guess. Similarly, your brain doesn't know what's going on in the outside world. All it's getting are wavelengths of light, changes in air pressure, concentrations of chemicals, and so on. Again, those are the effects of some set of causes. This is what philosophers call a reverse inference problem. So what is your brain using to solve the reverse inference problem, to guess at the causes of the sense data that will arrive in a moment from now? Past experiences.

As your brain attempts to solve the reverse inference problem, it is not asking itself, figuratively speaking “What is this?” Instead, it is asking something more akin to “What is this like?” “What is this similar to in my past experience?” Your brain is making guesses about what is going to happen next, so it knows how to act next to keep you alive and well. It’s continuously drawing on your past experiences to create your present. The really cool thing about this? It's really hard for people to change their past. However, by changing your present, you are cultivating a different future. By changing what you do and say, and feel, you are seeding your brain to predict differently in the future.

This gets us into all sorts of knotty questions about responsibility and free will.

The bottom line is we're more responsible for ourselves than we might think, and, as I discuss in the book, we're also more responsible for other people than we might think. Or want. You know, sometimes you're responsible for something not because the situation is your fault—you're responsible for something because you're the only person who can change the way things are. It's not an issue of culpability. The actions and the experiences that your brain makes today become your brain's predictions for tomorrow. So making an effort to cultivate new experiences and learn new things today is an investment in who you will be tomorrow. Some people have control over many things in their lives, and some people have less control because of their life circumstances, but everyone can control something.

There’s that example in your book of a man who mistakes a shepherd boy holding a herding stick for a guerilla fighter with a rifle, and almost shoots him before being stopped. In his subjective reality, which his brain has constructed, he’s taking aim at a militant fighter. In objective reality, he’s taking aim at a kid with some cows. How do we think about holding him accountable?

Well, in this case, responsibility is complicated because he was drafted into the army by the government. But what was true for him is true for all of us: what we see is a combination of what is going on out in the world and inside our own bodies, as well as what is going on inside our heads. I actually wrote about this in The New York Times. To the best of my knowledge, here is what the scientific evidence suggests: It is possible for a person to literally see a gun where there is no gun. So, if the soldier’s brain predicted that another person was holding a gun, and his heart was racing at 180 beats a minute, his brain would have had trouble sampling visual information from the world effectively. And the result would be that his brain would go with his prediction—and he sees a gun—instead of correcting the prediction with visual input of a stick, from the world. Think about what this might mean for the tsunami of problems in policing that we are grappling with right now.

An important consideration here: where do your brain’s predictions come from? Those predictions come from not just your own past experiences, but what you read and what you see in the news and what you watch on television and the social media that you're exposed to. That's where your predictions come from—from a world that others curate for you. As you get older, you have some choice in curating that world by what you expose yourself to (and what you don’t). We're getting into Lesson Seven in the book: we're social animals and we learn from each other. We don't just learn by doing, we also learn by telling stories and listening to one another. We communicate our own experiences to other people and other people learn from those experiences. So we don't have to go through the painful process of learning everything on our own. This social learning has serious benefits, but it also has some risks. This is one aspect of free will that few people talk about: You can broaden your experiences today to predict differently tomorrow. Effective control over your behavior requires that you broaden the horizon of time. Having control of your actions isn't only about avoiding certain actions “in the heat of the moment”—it’s also about seeding your brain to have more flexibility in constructing your predictions before the heat of the moment.

It’s important to understand what the scientific evidence is regarding how your brain controls your actions. You don't see stuff in the world and then draw a gun. Based on your brain’s best understanding of how the world is right now, your brain prepares your upcoming actions, like drawing a gun, taking aim, and so on, and that makes it more likely that you will literally see certain things, like a gun, if your brain has learned these associations in the past. That is how your brain works.

Obviously, this is a very anxious time with the election and coronavirus. I'm curious how you see your work in your first book, How Emotions Are Made, intersecting with this stressful moment.

To better understand anxious, stressed feelings, we have to return to your brain’s most important job: to control the systems of your body in an energy efficient way. You can think about energy efficiency like a budget. A financial budget tracks money as it’s earned and spent. A budget for your body similarly tracks resources like water, salt, and glucose as you gain and lose them. Every time your brain has to learn something new is like a withdrawal from your body budget. Actions that replenish your resources, such as eating and sleeping, are like deposits. What is stress? It is when your brain makes a withdrawal from the body budget. Good stress occurs when the withdrawal is followed by a deposit. Chronic stress is when your brain keeps spending and spending, without sufficient deposits, driving the body budget into a deficit. This is a simplified explanation, but it captures the key idea that running a body requires biological resources. Every action you take (or don’t take) is an economic choice—your brain is guessing when to spend resources and when to save them. Ditto for everything you learn (or don’t learn). (The scientific term for body budgeting is allostasis.)

Everything you think, feel, and do is a consequence of your brain’s central mission to keep you alive and well by managing your body budget. We don’t experience our every thought, every feeling of anxiety, happiness or anger or awe, every hug we give or receive, every kindness we extend, and every insult we bear as a deposit or withdrawal in our metabolic budgets, but under the hood, that is what’s happening.

When your brain can’t predict well—when there is too much uncertainty, for example—your brain may attempt to learn something new so that it can predict better next time. Learning involves the release of a whole set of chemicals, some of which are related to making you feel jittery and on edge. In the short term, learning is a good investment of energy, because it's likely to pay dividends in the future. The key is to replenish what you've spent, to keep your body budget solvent.

If the uncertainty goes on for too long maybe because of COVID fears, or economic uncertainty—if your body budget is being drained—you may end up running a deficit, which leaves you feeling constantly worked up and unpleasant. In our culture, we have learned to make sense of these feelings as anxiety. Making sense of uncomfortable, heightened arousal as anxiety might lead us to act in ways that only further burden our body budgets, rather than trying to pay down the debt by getting enough sleep, eating healthfully, giving and receiving support to loved ones, and so on. Eventually, this can sometimes lead to bigger problems. I mean, what do you do when your actual bank account is running a deficit?

Stop spending.

Right. What does that mean for a brain? It means that you stop moving your body as much and you stop learning. Think about the current social moment. Why does it feel better for people to surround themselves with other like-minded people in an echo chamber? Social media may help construct that chamber, but that’s not the whole story. Why don’t more people forage for novel information that does not conform to their beliefs? Perhaps because it’s metabolically expensive. And when your body budget's already encumbered because you're not sleeping enough or because there's tremendous amount of economic uncertainty, or you're worried about not being able to feed your kids, or you're worried about getting sick… You end up making lots of little withdrawals over time that are not made up by deposits—it’s like paying lots of little taxes that add up over time. And eventually, you could get a point where you are swimming in a sea of uncertainty or surfing a tsunami of stress. Persistent uncertainty is very, very hard on a human nervous system.

How does the idea of “emotional granularity” offset that? This idea that if we understand our world through the concepts that we have, then the more concepts we have, the better we can understand what we're feeling.

An emotion is an episode in which your brain uses what you know about emotion – emotion concepts – to make sense of the changes in your body (changes in heart rate, in breathing, and so on) by connecting these sense data and the feelings that they give rise to with what is going on around you in the world. This is how you might come to experience a tightness in your chest as anxiety, determination, or the physical symptoms of a respiratory infection. The more concepts you know, the more flexibly your brain can guess at might cause the sense data from your body in a given situation.

Concepts help you understand emotions after they have emerged, sure, but they are also a key ingredient of constructing emotions in the first place. Emotions don’t happen to you—they are made by your brain as you need them. They are not built into your brain at birth. They are built by your brain using the emotion concepts that you have learned. Using emotion concepts, your brain runs your body budget by predicting the causes of upcoming events in your body in a way that is linked to the situation that you are in, for the purposes of acting in a particular way. So ultimately, concepts are tools for making emotion. More generally, concepts are tools for making new meaning of the physical sensations from your body, in the context that you're in, to guide your actions in a particular way. And the result is sometimes an emotion. So emotional granularity doesn't mean that you just understand your emotions better. It means that you construct your emotions more precisely to fit the situation that you are in.

How does that change our experience of the world then? For example, if I were to say, “I'm not sad, I'm disappointed.”

To answer your question, we have to talk about affect. Your brain is constantly managing your body budget, and your body is constantly sending back sense data to your brain. This is happening right now, even though you are probably unaware of it. And that’s because you are not wired to consciously experience this continuous symphony of sense data. Evolution has given you a workaround, though: simple feelings of comfort or pleasantness, discomfort or unpleasantness, feeling wound up or tired. These simple feelings you might call mood. Scientists call them affect.

Let’s say you're running a body budget deficit. So you feel crappy. Let’s say you're not a very granular person and, for you, anger, sadness, fear are all synonyms of, “I feel like shit.” Well, what should you do next to deal with the situation? Your brain hasn’t made a very specific guess. Do you have a drink of water? Do you yell at someone? Do you go for a run? It’s hard to know because your brain hasn't made a concept that allows it to predict a specific action.

But if your brain has learned that sadness means you have lost something dear to you, whereas disappointment means that your hopes or expectations have been dashed—that is, when you have learned that sadness and disappointment are not synonyms, but are distinct concepts involving distinct actions—then making your affect meaningful with a concept for sadness will lead to very different actions than if your brain makes a concept for disappointment.

Here’s a trivial example: like many people in this country, I am weary and I am stressed. Under the hood, my brain is constructing concepts to predict and make sense of what is going on inside my body in relation to the situation I am in. My brain could construct an experience of anxiety, or depression, or hopelessness. But instead, it constructs a concept of an encumbered body budget. And this guides my actions. I need to make sure that I sleep and I need to make sure that I drink enough water. I need to make sure that I exercise, even though I really don't feel like it. I make sure to get enough social contact with those I love.

Emotional granularity is also knowing when not to make an emotion. Instead, my brain is making meaning of the sense data, and the affective feelings that they cause, as a physical phenomenon. And what does this granularity buy you? It buys you the flexibility to make sense of your sensations and act on them differently depending on the context, tailoring your actions to the situation you are in.


Why do we feel thirst in our throat but hunger in our stomach?

Why do we feel the snsation of thirst in our throats but hunger in our stomach it it because as the amount of water in our body becomes lower less saliva is created making the throat dry?

When you're dehydrated, your kidneys release a hormone called renin, which activates another hormone called angiotensin. These do a number of things in your kidneys to help conserve water, but angiotensin also reduces saliva production, which gives you a dry mouth/throat.

When your stomach is empty, cells in the GI tract release a hormone called ghrelin. Ghrelin acts on your brain to produce a feeling of hunger, and also stimulates acid production and muscle activity in the gut to prepare for incoming food. This muscle activity is what you are feeling when your stomach rumbles.

When your stomach is empty, cells in the GI tract release a hormone called ghrelin.

These diet pills that make you "not feel hungry". Are they just inhibiting that hormone in one way or another?

I remember reading a long time ago that people are not actually hungry, but thirsty, if they are craving things that are usually wet, or considered juicy. Is this still a valid view? Also, if that's the case, then if you feel hungry, but crave juicy things, could it be that you feel hungry when you're both thirsty and hungry, and it's just hard to interpret at times what you're stomach is trying to tell you from feeling alone?

In addition to the feeling of dryness caused by reduced saliva production, it should be noted that one of the high-pressure (arterial) baroreceptor clusters is in your throat, in the carotid sinus. This group of pressure-sensing cells relays information about your blood volume to your brain which in turn results in the hormonal regulation referred to by /u/akula457. The high pressure system maintains blood pressure when volume or posture changes would otherwise effect it.

When the volume of blood plasma you have in circulation is diminished (whether by sweating, excretion, blood loss, etc.) these cells report in and you have a thirst reflex (there are other low-pressure clusters of these cells in veins as opposed to arteries which act in concert). There is some evidence that you may have a low level sensation from this primary baroreceptor response in addition to whatever aftereffects are caused by the thirst reflex. This is backed up by the observation that some people can accidentally elicit responses from their baroreceptors when applying pressure from something like shaving, and these responses include feelings of thirst or nausea.

You sent me on a lovely trip through a Wikipedia maze about angiotensin and ghrelin. Thank you.

How do our bodies know when to stop releasing Ghrelin?

From what I understand the release of ghrelin has more to do with meal timing then whether or not your stomach is empty. In other words, you usually eat at a specific time so your body expects it and makes you feel hungry.

I was told that our stomach grumbles because that's the Pyloric Sphincter opening and closing in preparation for food. Is this correct?

What about when you ignore the hungry feeling until it goes away? Does your body stop producing ghrelin all together?

This is why the typical weight loss advice to chug water all day because your body can't distinguish hunger from thirst or regulate its own fluid balance is nonsense. Hunger and thirst are controlled by completely separate pathways. Drinking water by itself or with a meal doesn't make you significantly less hungry.

The results indicate that during free access to water humans become thirsty and drink before body fluid deficits develop, perhaps in response to subtle oropharyngeal cues, and so provide evidence for anticipatory thirst and drinking in man.

Decreasing the energy density of and increasing the volume of the preload by adding water to it significantly increased fullness and reduced hunger and subsequent energy intake at lunch. The equivalent amount of water served as a beverage with a food did not affect satiety.

I'm sure a combination of dopamine, ghrelin, and leptin (and others?) act together to induce feeding, but how does ignoring the signal to feed affect hunger and these levels of hormones?

If I haven't eaten all day, eventually my appetite actually becomes reduced. I feel like my body just accepts that it's not going to get food. How does this work? It must be more complex than the body becoming resistant that quickly to a hormone, right?

There are also additional sensory pathways that are somatized by the brain to indicate our sensation of "thirst" or "hunger." Basically it is just an interpretation of the brain that thirst is quenched by drinking, thus thirst is quenched by wetting the throat. Same sort of thing for the stomach and hunger.

More accurately it is just the reverse of the stimulus that triggers sensations in those parts of the body at all. The gut does not feel pain but it does feel stretch. Stretch in the stomach indicates it is full. Hunger can be triggered by many things (including conditioning, like "comfort food" or depressive eating) but a drop in available calories as signalled by changes in the biochemical milieu is what we are really talking about here. So, if your body's energy state is diminished, it sends the signal that more calories are needed. Calories come from food but they also take time to digest and get into your bloodstream. If that was the signal for satiety then we would always overeat, being hungry long after our stomachs are full. So the first signal to indicate satiety is fullness of the stomach, as indicated by the stretch receptors native to the organ.

The same is analogous for thirst. Water is absorbed much more quickly than food, but too much water can also be harmful. So the first signal that water needs are being met is mediated by receptors in the throat. These receptors can't be mechanical since food would also trigger them. Thus, it turns out that they are temperature sensitive. Which is why cold water feels more thirst quenching than warm water and why we give ice chips to patients who can't drink water the icy cold drips of water stimulate those receptors and tell your brain that thirst needs are being met.

edit I realize after re-reading that this isn't exactly perfectly clear and not exactly right in a couple of spots, but the general idea is correct and hopefully understandable. I just crossed out the part that isn't actually quite right. The rest should stand with that sentence removed.



Comments:

  1. Volker

    I'm sorry, this is not exactly what I need. Who else can suggest?

  2. JoJogal

    Should you tell you have deceived.

  3. Wiellaburne

    I still remember the age of 18

  4. Garen

    I don't even know what to say

  5. Merestun

    It is not clear

  6. Gresham

    the choice at home difficult



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