The effects of stimulating the cerebellum on social sequences: A tDCS-fMRI pilot study

Research on the involvement of the cerebellum in social behavior and its relationship with social mentalizing has just begun. Social mentalizing is the ability to attribute mental states such as desires, intentions, and beliefs to others. This ability involves the use of social action sequences which are believed to be stored in the cerebellum. In order to better understand the neurobiology of social mentalizing, we applied cerebellar transcranial direct current stimulation (tDCS) on 23 healthy participants in the MRI scanner, immediately followed by measuring their brain activity during a task that required to generate the correct sequence of social actions involving false (i.e., outdated) and true beliefs, social routines and non-social (control) events. The results revealed that stimulation decreased task performance along with decreased brain activation in mentalizing areas, including the temporoparietal junction and the precuneus. This decrease was strongest for true belief sequences compared to the other sequences. These findings support the functional impact of the cerebellum on the mentalizing network and belief mentalizing, contributing to the understanding of the role of the cerebellum in social sequences. (AU)

Can transcranial direct current stimulation (tDCS) of the cerebellum improve implicit social and cognitive sequence learning?

Accumulating evidence shows that the posterior cerebellum is involved in mentalizing inferences of social events by detecting sequence information in these events, and building and updating internal models of these sequences. By applying anodal and sham cerebellar transcranial direct current stimulation (tDCS) on the posteromedial cerebellum of healthy participants, and using a serial reaction time (SRT) task paradigm, the current study examined the causal involvement of the cerebellum in implicitly learning sequences of social beliefs of others (Belief SRT) and non-social colored shapes (Cognitive SRT). Apart from the social or cognitive domain differences, both tasks were structurally identical. Results of anodal stimulation (i.e., 2 mA for 20 min) during the social Belief SRT task, did not show significant improvement in reaction times, however it did reveal generally faster responses for the Cognitive SRT task. This improved performance could also be observed after the cessation of stimulation after 30 min, and up to one week later. Our findings suggest a general positive effect of anodal cerebellar tDCS on implicit non-social Cognitive sequence learning, supporting a causal role of the cerebellum in this learning process. We speculate that the lack of tDCS modulation of the social Belief SRT task is due to the familiar and overlearned nature of attributing social beliefs, suggesting that easy and automatized tasks leave little room for improvement through tDCS. (AU)

Social thinking is for doing: the posterior cerebellum supports predictions of social actions based on personality traits.

Can we predict the future by reading others' minds? This study explores whether attributing others' personality traits facilitates predictions about their future actions and the temporal order of these future actions. Prior evidence demonstrated that the posterior cerebellar crus is involved in identifying the temporal sequence of social actions and the person's traits they imply. Based on this, we hypothesized that this area might also be recruited in the reverse process; that is, knowledge of another person's personality traits supports predictions of temporal sequences of others' actions. In this study, participants were informed about the trait of a person and then had to select actions that were consistent with this information and arrange them in the most likely temporal order. As hypothesized, the posterior cerebellar crus 1 and crus 2 were strongly activated when compared to a control task which involved only the selection of actions (without temporal ordering) or which depicted non-social objects and their characteristics. Our findings highlight the important function of the posterior cerebellar crus in the prediction of social action sequences in social understanding.

Author Correction: Neural representations of Groups and Stereotypes using fMRI repetition suppression.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.