Food neophobia correlates with motor cortex excitability in response to disgust-related stimuli

Disgust is a negative emotion that can trigger rejection mechanisms which are important for survival when the disgusting stimulus is spoiled/contaminated food. In this context the anterior digastric (AD) muscle by opening the jaw has a role in expelling potentially harmful substances from the mouth. Whether disgusting gustative stimuli affect the excitability of the primary motor cortex (M1) innervating AD muscle is not known. In this study, by applying transcranial magnetic stimulation protocol, short-interval intracortical inhibition (SICI) was measured in AD M1, during passive viewing of pictures representing either unspoiled or spoiled food. As control disgusted or happy face expressions were also administered. To evaluate a specific muscle effect, the experiment was also performed in the first dorsal interosseous (FDI) representation area in M1. Disgust sensitivity, food neophobia and adherence to Mediterranean Diet were evaluated by validated questionnaires. Results evidenced that the passive view of gustatory disgust images does not modulate the excitability of AD M1. Correlation analysis showed an enhanced cortical excitability of the M1 innervating FDI, during the passive view of spoiled food, in higher food neophobic participants. This suggests that food neophobia could facilitate recognition of disgusting/rotten food and elicit avoidance mechanisms involving the hand but not the AD, associating for the first time, the heritable trait food neophobia with differences in M1 excitability.