+ May 22, 2014
Science Daily/ETH Zürich
We are all familiar with that uncomfortable feeling in our stomach when faced with a threatening situation. By studying rats, researchers have been able to prove for the first time that our ‘gut instinct’ has a significant impact on how we react to fear. An unlit, deserted car park at night, footsteps in the gloom. The heart beats faster and the stomach ties itself in knots. We often feel threatening situations in our stomachs. While the brain has long been viewed as the center of all emotions, researchers are increasingly trying to get to the bottom of this proverbial gut instinct.
It is not only the brain that controls processes in our abdominal cavity; our stomach also sends signals back to the brain. At the heart of this dialogue between the brain and abdomen is the vagus nerve, which transmits signals in both directions -- from the brain to our internal organs (via the so called efferent nerves) and from the stomach back to our brain (via the afferent nerves). By cutting the afferent nerve fibres in rats, a team of researchers led by Urs Meyer, a member of staff in the Laboratory of Physiology & Behaviour at ETH Zurich, turned this two-way communication into a one-way street, enabling the researchers to get to the bottom of the role played by gut instinct. In the test animals, the brain was still able to control processes in the abdomen, but no longer received any signals from the other direction.
Less fear without gut instinct
In the behavioural studies, the researchers determined that the rats were less wary of open spaces and bright lights compared with controlled 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," says Meyer.
Stomach influences signalling in the brain
"A lower level of innate fear, but a longer retention of learned fear -- this may sound contradictory," says Meyer. However, innate and conditioned fear are two different behavioural domains in which different signalling systems in the brain are involved. On closer investigation of the rats' brains, the researchers found that the loss of signals from the abdomen changes the production of certain signalling substances, so called 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 behavioural patterns. This has traditionally been attributed to the brain alone," says Meyer. The study shows clearly that the stomach also has a say in how we respond to fear; however, what it says, i.e. precisely what it signals, is not yet clear. The researchers hope, however, that they will be able to further clarify the role of the vagus nerve and the dialogue between brain and body in future studies.