The role of the somatosensory system in the processing of emotions: a transcranial alternated stimulation (tACS) study

Emotional experiences have a deep impact on our bodily states, such as when we feel ‘fear’ our body feels cold and unable to move, and when we feel ‘anger’ we close our fists and feel our face burning. Recent behavioural studies have shown that emotions can be mapped onto specific body portions, suggesting that emotions are represented in the somatosensory system. However, what is the role of the somatosensory system in the processing of emotions and, more specifically, in the generation of feelings of emotions? To answer this question, we applied transcranial alternated current stimulation (tACS) to the somatosensory cortex of healthy adult participants at different frequencies while they saw emotional pictures taken from the IAPS database. We found that modulation of cortical excitability of S1 influenced subjective emotional ratings, particularly affecting Valence, and making the participants rating more pleasant, instead, we didn’t find a clear effect on Arousal (measured through the skin conductance response). Our results suggest a dissociation between the two dimensions of emotions: Arousal and Valence, with the latest being the only one affected by tACS applied on S1 at different frequencies. This is compatible with previous studies suggesting different neural substrates for Valence and Arousal, in which the Orbitofrontal cortex process valance and the amygdala preferentially process arousal. In general, our findings suggest that the somatosensory system plays a crucial role in the generation of emotions.