Dr Emeran Mayer: Your Gut Processes Emotion and Regulates Health While You Sleep

Your brain isn't the only organ processing your day while you sleep. Dr. Emeran Mayer explains the circular processing of emotion and memory that goes on between your brain and your digestive system, and how the latter can "dream".

Emeran Mayer:  So when we sleep and we have an empty stomach then the activity, the contractile activity of our gut changes to a very unique pattern. It’s a 90-minute cycle, very powerful waves of contractions migrate from the esophagus all the way down to the end of our large intestine. And they move very slowly. So this has been referred to as the intestinal housekeeper that sort of cleans the gut from any residue that’s present. And the rhythm for that is generated by the brain so it’s dependent on the input of the vagus nerve on the second brain in the gut. And this has been something that also should occur when during daytime when in between meals when our stomach and intestinal system is empty.

However with the sort of modern habit of snacking in between meals so a lot of people don’t have that during the day but have it during sleep. If you add the microbes into this now it’s quite likely, not really proven. I mean the microbes obey some kind of a Circadian rhythm by themselves so they’re different during sleep and during daytime. But it’s quite possible to assume that this powerful wave that sort of cleans everything out will also affect the microbes, the composition of the microbes because if we don’t have it – so people that don’t have that for some reason they will develop abnormal colonization, for example, of their small bowel with a lot of microbes that don’t really belong there. So clearly an important role in regulating the populations and the regional distribution of these microbes in our gut. What happens during sleep, so during REM sleep when we have a lot of activity going on within the autonomic nervous system circuits within the brain and the signals are being sent to the gut. So our body is inhibited but not our intestinal activity.

So in many ways emotions that we experience usually in our dreams have their mirror image in terms of gut activity – contractions, secretions. And again I mean like everything that goes on within our brain emotionally always is reflected just like our facial expression reflects our emotions, everything reflects our emotional state either during waking time or sleep time at the gut level. And the microbes who live in that environment are affected by it. So it’s an area that’s not studied in great detail but very important for an understanding of how the microbes, the gut and the brain interact and maintain health. So sleep is a very important ingredient for health regulation of the immune system but for the also regulation of gut function and particularly gut microbial integrity and wellbeing.

We know quite a bit about what happens during sleep and during dreaming. In psychoanalysis this is a big window into our emotional lives so Jungian or Freudian psychoanalysts have spent a lot of time interpreting dreams and getting an access to this process. A big portion is probably the processing and consolidation of memories that have been experienced during the day. Many of these memories have a gut feeling component because every time we have an emotion during the day there’s always a counterpart at the gut level that is then through these sensory pathways goes back to the brain. We may not experience it during the daytime but it’s encoded in this vast database within the brain. So what happens then during sleep there is this retrieval and then processing and consolidation of these memories including all the gut feelings that are associated with those experiences that we had during the day.

I think it’s a very important point to emphasize that emotions have an intricate component of gut activity and gut feelings regardless if you feel it like the butterflies in the stomach or the knot in the stomach. Every emotion has a component that the brain engages gut activity and that’s being reported back to the brain. And so you have to look at an emotion really as a circular process within the brain-gut access. And during sleep and during dreaming there’s almost certainly a consolidation processing of this myriad of gut feelings that are generated throughout the day.

There is so much more going on in your sleep than you think.


In his first video for Big Think, Dr Emeran Mayer – gastroenterologist and author of The Mind-Gut Connection – described what is called our "second brain". The gut is no ordinary body system; it’s intelligent and independent, in that it consists of about 100 million nerve cells sandwiched between layers of the gut running all the way from the esophagus to the end of the large intestine. This ‘second brain’ in our gut, and our regular brain use the same neurotransmitters and are connected through neural, endocrine, and immune pathways, so it truly is an integrated intelligent system with information flowing in both directions.

This becomes interesting when you start asking questions about sleep and its relationship to health. We all know sleep is vital to bodily function, but usually we’re focused on our mind activity. What are we dreaming about? Are we processing the day’s emotional turbulences? Are we getting enough sleep to let the brain do its thing?

Dr. Mayer explains that your gut is also critically important during sleep, and is affected by your sleep patterns. When you fall asleep and your stomach is empty, your gut commences 90-minute cycles of intense contractile waves that migrate from your esophagus all the way down to the end of your large intestine. It’s a cleaning process that removes residue from the gut and keeps microbial bacteria in check. We’ve always known that missing out on sleep makes us foggy-headed and far from our best selves in terms of cognition, but if our sleep is disturbed or we aren’t getting enough of it, or we are eating too much in the night, the gut won’t have a chance to properly clean itself. Left unregulated, bacteria will develop into abnormal colonies, the health implications of which can be enormous.

What’s more, Mayer points out that, in a way, your gut dreams too. Just as the expressions on your face reveal your internal emotions, your gut is equally reflective of your daily ups and downs – whether it takes the form of butterflies, nervous bowels, emotional nausea, or more subtle physiological changes that fly under the radar. And just as an event that didn’t really seem important in the daytime can completely take over your dreams at night, your gut too is encoded with these experiences and must digest them. "Many of these memories have a gut-feeling component because every time we have an emotion during the day there’s always a counterpart at the gut level that, through these sensory pathways, goes back to the brain." During sleep, memories are retrieved and processed in the brain, which includes re-living the corresponding gut feelings we had during the day.

With this insight, one has a whole new appreciation for the gut or "second brain", and its nocturnal mechanisms are a fascinating and urgent reminder that sleep is more important than ever.

Dr Emeran Mayer's most recent book is The Mind-Gut Connection: How the Hidden Conversation Within Our Bodies Impacts Our Mood, Our Choices, and Our Overall Health

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Yale scientists restore brain function to 32 clinically dead pigs

Researchers hope the technology will further our understanding of the brain, but lawmakers may not be ready for the ethical challenges.

Still from John Stephenson's 1999 rendition of Animal Farm.
Surprising Science
  • Researchers at the Yale School of Medicine successfully restored some functions to pig brains that had been dead for hours.
  • They hope the technology will advance our understanding of the brain, potentially developing new treatments for debilitating diseases and disorders.
  • The research raises many ethical questions and puts to the test our current understanding of death.

The image of an undead brain coming back to live again is the stuff of science fiction. Not just any science fiction, specifically B-grade sci fi. What instantly springs to mind is the black-and-white horrors of films like Fiend Without a Face. Bad acting. Plastic monstrosities. Visible strings. And a spinal cord that, for some reason, is also a tentacle?

But like any good science fiction, it's only a matter of time before some manner of it seeps into our reality. This week's Nature published the findings of researchers who managed to restore function to pigs' brains that were clinically dead. At least, what we once thought of as dead.

What's dead may never die, it seems

The researchers did not hail from House Greyjoy — "What is dead may never die" — but came largely from the Yale School of Medicine. They connected 32 pig brains to a system called BrainEx. BrainEx is an artificial perfusion system — that is, a system that takes over the functions normally regulated by the organ. The pigs had been killed four hours earlier at a U.S. Department of Agriculture slaughterhouse; their brains completely removed from the skulls.

BrainEx pumped an experiment solution into the brain that essentially mimic blood flow. It brought oxygen and nutrients to the tissues, giving brain cells the resources to begin many normal functions. The cells began consuming and metabolizing sugars. The brains' immune systems kicked in. Neuron samples could carry an electrical signal. Some brain cells even responded to drugs.

The researchers have managed to keep some brains alive for up to 36 hours, and currently do not know if BrainEx can have sustained the brains longer. "It is conceivable we are just preventing the inevitable, and the brain won't be able to recover," said Nenad Sestan, Yale neuroscientist and the lead researcher.

As a control, other brains received either a fake solution or no solution at all. None revived brain activity and deteriorated as normal.

The researchers hope the technology can enhance our ability to study the brain and its cellular functions. One of the main avenues of such studies would be brain disorders and diseases. This could point the way to developing new of treatments for the likes of brain injuries, Alzheimer's, Huntington's, and neurodegenerative conditions.

"This is an extraordinary and very promising breakthrough for neuroscience. It immediately offers a much better model for studying the human brain, which is extraordinarily important, given the vast amount of human suffering from diseases of the mind [and] brain," Nita Farahany, the bioethicists at the Duke University School of Law who wrote the study's commentary, told National Geographic.

An ethical gray matter

Before anyone gets an Island of Dr. Moreau vibe, it's worth noting that the brains did not approach neural activity anywhere near consciousness.

The BrainEx solution contained chemicals that prevented neurons from firing. To be extra cautious, the researchers also monitored the brains for any such activity and were prepared to administer an anesthetic should they have seen signs of consciousness.

Even so, the research signals a massive debate to come regarding medical ethics and our definition of death.

Most countries define death, clinically speaking, as the irreversible loss of brain or circulatory function. This definition was already at odds with some folk- and value-centric understandings, but where do we go if it becomes possible to reverse clinical death with artificial perfusion?

"This is wild," Jonathan Moreno, a bioethicist at the University of Pennsylvania, told the New York Times. "If ever there was an issue that merited big public deliberation on the ethics of science and medicine, this is one."

One possible consequence involves organ donations. Some European countries require emergency responders to use a process that preserves organs when they cannot resuscitate a person. They continue to pump blood throughout the body, but use a "thoracic aortic occlusion balloon" to prevent that blood from reaching the brain.

The system is already controversial because it raises concerns about what caused the patient's death. But what happens when brain death becomes readily reversible? Stuart Younger, a bioethicist at Case Western Reserve University, told Nature that if BrainEx were to become widely available, it could shrink the pool of eligible donors.

"There's a potential conflict here between the interests of potential donors — who might not even be donors — and people who are waiting for organs," he said.

It will be a while before such experiments go anywhere near human subjects. A more immediate ethical question relates to how such experiments harm animal subjects.

Ethical review boards evaluate research protocols and can reject any that causes undue pain, suffering, or distress. Since dead animals feel no pain, suffer no trauma, they are typically approved as subjects. But how do such boards make a judgement regarding the suffering of a "cellularly active" brain? The distress of a partially alive brain?

The dilemma is unprecedented.

Setting new boundaries

Another science fiction story that comes to mind when discussing this story is, of course, Frankenstein. As Farahany told National Geographic: "It is definitely has [sic] a good science-fiction element to it, and it is restoring cellular function where we previously thought impossible. But to have Frankenstein, you need some degree of consciousness, some 'there' there. [The researchers] did not recover any form of consciousness in this study, and it is still unclear if we ever could. But we are one step closer to that possibility."

She's right. The researchers undertook their research for the betterment of humanity, and we may one day reap some unimaginable medical benefits from it. The ethical questions, however, remain as unsettling as the stories they remind us of.

Scientists see 'rarest event ever recorded' in search for dark matter

The team caught a glimpse of a process that takes 18,000,000,000,000,000,000,000 years.

Image source: Pixabay
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