The chronometry of cerebellar recruitment in processing emotional faces: A study with transcranial magnetic stimulation.

Recent literature has established the involvement of the cerebellum, particularly the left posterior cerebellar area, in affective functions and social cognition, including the processing of emotional facial expressions. Its involvement has been proposed to reflect supportive functions to cortical areas, such as the superior temporal sulcus (STS), an area that has been consistently implicated in the processing of emotional facial expressions and in mirroring functions. The nature of the involvement of the cerebellum as well as its specific functional relationship with other areas implicated in socio-affective processing, however, is still debated. This thesis addresses this issue by investigating the chronometry of cerebellar involvement in the processing of emotional facial expressions through TMS. Specifically, we delivered TMS over the left posterior cerebellum (and two control regions) with pulse delivery at four discrete time windows during the performance of an emotional expression discrimination task: From 20-120ms, 120-220ms, 220-320ms and 320-420ms from the appearance of the image. Our results showed that rTMS over the left posterior cerebellum resulted in a decrease of participant’s accuracy in the discrimination task when delivered between 120 and 220ms from stimulus onset. These results converged with previous studies in showing that the cerebellum causally contributes to the discrimination of emotional facial expressions, and they reveal that it does so in a specific time window that follows the early V1/V2 involvement (demonstrated to be around 20-120ms) and partially overlaps with STS involvement (shown by previous studies to occur around 60-140ms).