Your gut’s ‘second brain’ may have evolved before your head’s brain
The nervous system found in the gut, called the enteric nervous system (ENS), works in a similar way to the neural networks found in the brain and spinal cord - leading to its nickname as the body’s ‘second brain’.
A new study, published in Communications Biology, has revealed more about how the ENS works, as well as evidence for the claim it evolved before the brains in our heads did.
By studying the colons of mice, particularly how the gut moves its contents along, scientists discovered that thousands of neurons inside the ENS communicate with each other.
This causes the gastrointestinal tract to contract and helps digestion.
The ‘brain-gut’ connection between the first brain (in the head) and the second brain (in the gut). Image: Getty Images
Until now, it was unclear how these neurons worked together to do this.
“Interestingly, the same neural circuit was activated during both propulsive and non-propulsive contractions,” says Nick Spencer, a neurophysicist at Flinders University in Australia and the lead author of the paper.
The researchers found the contents of the gut was moved further along it by the firing of large bunches of connecting neurons, with both excitatory (action-causing) and inhibitory (blocking) motor neurons involved.
This means that the ENS is made up of a more advanced network of neurons that cover a wider section of the gut and involve a greater variety of neurons working together than had previously been thought.
Additionally, the team found that this activity is significantly different from the propulsion that occurs in other muscle organs that don’t have a built-in nervous system, such as lymphatic vessels, ureters, or the portal vein.
“The mechanism identified is more complex than expected and vastly different from fluid propulsion along other hollow smooth muscle organs,” the researchers explain in the paper.
The scientists say these findings support the hypothesis that the ENS is actually the ‘first brain’ rather than the second - suggesting it may have evolved in animals before our actual brains.
If the hypothesis is true, it could have implications beyond mouse guts, although further research is needed to determine how the ENS affects the workings of the gastrointestinal tract in different species.
“Synchronisation of neuronal activity across large populations of neurons is common in the nervous system of many vertebrate animals,” Spencer says.