While the brain is viewed as the center of emotions, fear and other threats are often felt in the stomach — the well-known gut instinct.
Transmitting signals between the brain and stomach is the vagus nerve, sending signals from our brain to our internal organs via the efferent nerves and from the stomach back to our brain via the afferent nerves.
To get a better understanding of gut instinct, researchers at ETH Zurich cut the afferent nerve fibers in rats. This meant the rats’ brains could still control processes in the abdomen, but the brain no longer received signals from the abdomen.
The researchers found that the rats were less wary of open spaces and bright lights compared with control rats with an intact vagus nerve.
“The innate response to fear appears to be influenced significantly by signals sent from the stomach to the brain,” said Urs Meyer, who led the research team.
He noted the loss of their gut instinct did not make the rats completely fearless. In a conditioning experiment, the rats learned to link a neutral acoustic stimulus — a sound — to an unpleasant experience. In this instance, the path between the stomach and brain appeared to play no role, with the test animals learning the association as well as the control animals.
If, however, the researchers switched from a negative to a neutral stimulus, the rats without gut instinct required significantly longer to associate the sound with the new, neutral situation.
“This also fits with the results of another recently published study that found that stimulation of the vagus nerve facilitates relearning,” Meyer said.
On closer examination of the rats’ brains, the researchers found that the loss of signals from the abdomen changed the production of neurotransmitters in the brain.
“We were able to show for the first time that the selective interruption of the signal path from the stomach to the brain changed complex behavioral patterns. This has traditionally been attributed to the brain alone,” he said.
While the study shows that the stomach has a say in how we respond to fear, precisely what it signals is not yet clear, according to the researchers. They said they hope they will be able to further clarify the role of the vagus nerve and the dialogue between brain and body in future studies.
Source: ETH Zurich