When it comes to understanding our moods and emotional responses, our brain is usually the first place we start digging.
One Florida State University neuroscientist thinks we're missing the big picture, arguing the meandering nerve that connects our head with our gut has a powerful influence on our behaviour. And we really need to be paying attention.
"The neuroscience of gut feelings has come a long way in my lifetime," says, Linda Rinaman, the author of a recently published review on the biology of gut reactions.
"And we are learning more valuable lessons every day."
The basic premise isn't all that new – we've suspected for more than a century now that the diverse metabolic, hormonal, and immunological interactions of the digestive system have a complicated two-way relationship with the emotional parts of our central nervous system.
Even the mid-20th century origins of terms like 'gut reaction' and 'gut feeling' have their roots in the visceral sensations that bubble up when we're feeling emotional.
Just how the two systems relate to one another, however, has proven difficult to tease apart.
The gastro-intestinal tract has around 100 times the surface area of our outer skin, and demands a lot of attention from the nervous system.
To manage this, signals run back and forth along a nerve that swerves back and forth from organ to organ up through the body.
Called the vagus nerve – Latin for 'wandering' – this super highway of nervous signalling monitors everything from digestion to heart rate to hormonal responses to immune functions.
While it's clear that there's quite an involved conversation going on down this internal telephone line, there is still some debate over just how much the gut affects our decision making.
Together with her colleague James Maniscalco from the University of Illinois in Chicago, Rinaman trawled the current banks of research to sum up where current thinking is at on the role of the vagus nerve on behaviour.
They argue signals from our gastrointestinal tract can put the brakes on rewarding behaviours to reinforce actions that lead us to avoid certain situations.
This makes sense in most animal models; feedback from what we're putting into our stomachs and intestines could certainly constitute a life-saving stop-signal.
"We know the gut-brain pathways are very similar across mammalian species – from mouse to human," says Rinaman, suggesting we have little reason to conclude similar GI biases aren't gently guiding our own actions.
Unlike mice, however, humans are considered to be a little more cerebrally complex, with an ability to apply reason and interpersonal communication to evaluate threats.
If our guts are affecting our decision making, knowing exactly where the gut's influence stops and cognitive processes begins is important.
In recent years we've been finding out just how much the gut's ecosystem of microbes could be directly affecting our health and mental wellbeing.
Not only do they seem to have the potential to kick off neurological conditions such as Parkinson's disease or even autism, their constitution could be fiddling with our emotional and cognitive states.
"Evidence shows that modifying the diet, perhaps by consuming probiotics, can impact your mood and behavioural state," says Rinaman.
"But how does that work? Does it involve the microbiome that you feed in your gut and how those bacteria send signals back to the brain through the vagus nerve? That area of research has exploded in the last few years and, currently, there are many more questions than answers."
The review is less a revolutionary discovery and more a call for a closer look at the finer details of how our guts tell our brains what to do.
Having better models could provide ways to treat various psychological and neurological conditions, perhaps targeting our microflora with tailored diets or stimulating the vagus nerve with pharmaceuticals.
Science works best when we apply liberal doses of critical thinking and reason. On this occasion, we advise we go with our gut for a change.
This research was published in Physiology.