That ‘gut feeling’ explained

By severing the brain-gut communication channel, researchers have got to the bottom of the proverbial gut instinct when it comes to fear. Communication between the brain and gut occurs via the vagus nerve, which transmits signals from the brain to internal organs (the efferent nerves) and from the stomach back to the brain (the afferent nerves). By cutting the afferent nerve fibres in rats, a team of researchers from ETH Zurich found the rodents were less wary of danger. “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 study. In conditioning experiments, the rats learned to link a neutral acoustic stimulus to an unpleasant experience. Test animals learned the association as well as the control animals, suggesting the stomach-brain pathway played no role here. However, when switching from an unpleasant stimulus to a neutral one, rats without this ‘gut instinct’ required significantly longer to associate the sound with a new, neutral stimulus. “A lower level of innate fear, but a longer retention of learned fear – this may sound contradictory,” said Meyer, before pointing out that two different behavioural domains in which different signalling systems in the brain are involved. Closer investigation of the rodents’ brains revealed 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 behavioural patterns,” Meyer said. “This has traditionally been attributed to the brain alone,” The research, published in The Journal of Neuroscience shows that the stomach clearly has a role to play in how were respond to fear, but exactly what it signals is not yet know, The team hope that they will be able to clarify the role of the vagus nerve and communication between the brain and body in further studies. Gut vagal afferents differentially modulate innate anxiety and learned fear