Distinct neural coding of action valence and intensity in the insula and amygdala

In social interactions, an essential part of communication involves shaping our actions or tone of voice to convey our mood, attitude, and affect. Depending on a positive or negative attitude, an individual may perform the same action with different Vitality Forms (VFs), for instance, gently or rudely. Although VFs characterize every human action, how the brain encodes these nuances remains unclear. To address this issue, we investigated cortical and subcortical brain activity during the observation of different VFs. In particular, an fMRI study in which participants observed arm actions combined with facial expressions performed with four different VFs, varying in valence (positive or negative) and intensity (low or high), was performed. Results revealed three main findings: a) the encoding of VFs involves the activation of the dorso-central insula (DCI), middle cingulate cortex (MCC), and amygdala; b) VFs valence is encoded in the left DCI, while the VFs intensity is encoded in the amygdalae, bilaterally; c) BOLD activity was significantly associated with participants' ratings of the stimuli. Specifically, valence scores were negatively linked to activation in the insula, whereas intensity scores were positively associated with amygdala BOLD responses, suggesting a specific relationship between stimulus properties and brain activity. Together, these findings provide new insight into how the brain processes VFs conveyed simultaneously through facial and arm movements, highlighting distinct regions involved in encoding their valence and intensity and their relationship with the subjective evaluation of affective meaning.