When people talk about “gut feelings”- something they can’t really rationalize, but feel as though the emotion is “coming from the heart” or “I feel it in my guts”, are those feelings actually coming from the heart or gut?

Well no.

But this doesn’t mean that the heart and gut do not influence our moods, decisions, and behavior. They do, especially the gut.

How could the gut possibly influence our minds, and why?

First let’s address the question of why.

Although we often tend to treat our bodies as just something to walk our minds around, our bodies are important parts of who we are (for an account of what it is like to lose a sense of your body, see “The Disembodied Lady”, by Oliver Sacks, in The Man Who Mistook His Wife For A Hat).

But the gut is special! That is, if you are any kind of a complex animal, you have to have one. Even tardigrades, the super tough little animals that can survive extreme conditions, like being frozen to -300 degrees Kelvin, or being subjected to radiation in Space, have a gut. No heart or lungs, but they do have a gut.

Two tardigrades.

For us more complex animals, we need our guts to digest and absorb nutrients. This frees our brains to engage in more interesting things: art, music, building things, being social… and on and on.

Other important things happen in the gut beyond absorbing nutrients (as important as that is). For instance, some cells of the immune system are “programmed” there, and their interactions with the cells and microbes in the gut influence their later functions. The cells can become inflammatory, or regulatory/ anti-inflammatory. This has implications for tissues beyond the gut, and contributes to risk for asthma, allergy, and autoimmune disease.

But still- why do things that go on in the gut influence our mood and behavior?

Perhaps because when things go wrong in the gut, it has no way to tell the brain specifically what is wrong. So it just signals that something is not right, driving the experience of anxiety (especially). And anxiety is a normal response to something not being right. Of course it would sure be nice to know what exactly is wrong in the gut, but knowing that gut problems can drive anxiety symptoms can help understand the etiology of treatment resistant anxiety, and suggest possible treatments (more on that in a future blog).

So how does this work?

The gut is full of nerves. Some of them of them are “intrinsic”- that is they are part of the guts own nervous system (alias The Gut-Brain, or enteric nervous system), and some are “extrinsic” and come from the brain and spinal cord (sympathetic and parasympathetic). These nerves both influence GI function (motor) or report back to the brain on things that are happening in the gut (sensory). Of the two types, sensory nerves predominate. This implies that the brain is VERY interested in what is going on in the gut.

This sensory information from the gut (interoception)is important in regulating things like physiology and eating behavior (knowing when we are hungry, or when we have eaten enough). But the information from the gut also drives activity in brain regions and neural circuits involved in emotions, memory, stress and coping.

It can sometimes really feel like our emotions are coming from our gut. This is because we perceive our own emotions via a Brain-Body-Brain loop. Emotions are generated in subcortical brain regions that, among other things, influence the autonomic nervous system that controls physiological functioning. Then we perceive the results of that activity, such as sweaty palms or butterflies in the stomach, and attribute it to anxiety, for instance. Our ability to notice these physical effects of emotions seem to be important for psychological health, and decision making, because when there are damage or poor functioning in brain regions involved in this process, people are not able to deal with emotions or learn from the consequences of bad decisions.

Interestingly, and importantly, some to the brain regions and circuits influenced by the gut are part of what is called the brain’s default mode, which (to make a long story short) turns out to be very important in constructing our sense of self. So- our sense of our selves is more than a mental construct. It includes our bodies, and especially our guts.

“We are what eat” in more ways than one!