The social role of the posterior cerebellum: an fMRI and tDCS study involving participants with autism spectrum disorder

For decades the cerebellum has been considered as solely involved in motor functions. However, recent work has revealed that this region also supports social processes, especially social sequencing. Social processes encompass the “Theory of Mind” (or mentalizing), a function that allows the awareness of others' mental states and engages the default/mentalizing network. This network involves some areas of the cerebral cortex (e.g. Superior Temporal Cortex, Temporo Parietal Junction), as well as some posterior areas of the cerebellum (especially Crus I/II). Furthermore, Autism Spectrum Disorder (ASD) is linked to mentalizing because of the social difficulties it entails and the similar brain areas that are engaged (including the cerebellum). In fact, not only subjects with ASD find difficulties in social interactions, but cerebellar dysfunctions are found to be a significant risk factor for ASD. The present study investigates the effect of tDCS stimulation on the posterior cerebellum of participants with ASD using a Pictorial Sequencing Task, which requires mentalizing. To each participant, prior to the task execution, we delivered anodal tDCS to the right posterior cerebellum in one session, and a false stimulation in the other session. The reaction time data revealed slower responses for the session with stimulation as compared to the session with sham. Moreover, at an exploratory level, this report investigates the cerebro-cerebellar areas that activate during social mentalizing functions of one participant. fMRI results confirmed the activation of the posterior cerebellum (especially Crus I/II) in tasks involving social mentalizing, together with the cerebral mentalizing areas with which the cerebellum interacts.