The posterior cerebellum supports implicit learning of social belief sequences

Abstract

Recent studies have documented the involvement of the posterior cerebellar Crus (I & II) in social mentalizing, when sequences play a critical role. We investigated for the first time implicit learning of belief sequences. We created a novel task in which true and false beliefs of other persons were alternated in an adapted serial reaction time (SRT) paradigm (Belief SRT task). Participants observed two protagonists whose beliefs concerning reality were manipulated, depending on their orientation toward the scene (true belief: directly observing the situation) or away from it (false belief: knowing only the prior situation). Unbeknownst to the participants, a fixed sequence related to the two protagonists' belief orientations was repeated throughout the task (Training phase); and to test the acquisition of this fixed sequence, it was occasionally interrupted by random sequences (Test phase). As a nonsocial control, the two protagonists and their orientations were replaced by two different shapes of different colors respectively (Control SRT task). As predicted, the posterior cerebellar Crus I & II were activated during the Belief SRT task and not in the Control SRT task. The Belief SRT task revealed that Crus I was activated during the initial learning of the fixed sequence (Training phase) and when this learned sequence was interrupted by random sequences (Test phase). Moreover, Crus II was activated during occasional reappearance of the learned sequence in the context of sequence violations (Test phase). Our results demonstrate the contribution of the posterior cerebellar Crus during implicit learning and predicting new belief sequences. Keywords Serial reaction time task . False belief . Social sequence learning . Cerebellum . Social cognition Highlights • The posterior cerebellum Crus (I & II) is engaged in implicit belief sequence learning. • The temporo-parietal junction also is activated to support implicit belief sequence learning. • The posterior cerebellum plays a sequence detection role in social domains.

The posterior cerebellum and temporoparietal junction support explicit learning of social belief sequences

“…However, unlike that study in which participants were not informed about the presence of a standard sequence (implicit instruction; hereafter termed "implicit" SRT tasks), participants were now explicitly told that there was a standard sequence (explicit instruction; hereafter termed "explicit" SRT tasks). Similar to the previous study (Ma, Pu, et al, 2021b), we hypothesized that the posterior cerebellar Crus I & II and cortical TPJ will be more activated in the explicit Belief SRT task than in the explicit Control SRT task as these two areas are preferentially engaged in social contexts (Hypothesis 1).…”

“…Faster response times were correlated with less Crus II activation and with more TPJ activation, suggesting that the Crus II supported automatizing the belief sequence while the TPJ supported inferring the protagonists' beliefs. Also as hypothesized, compared with an implicit version of the Belief SRT task (i.e., participants did not know about the existence of sequences; Ma, Pu, et al, 2021b), the cerebellar Crus I &II was engaged less during initial training and automatic application of the sequence, and the cortical TPJ was activated more in processing random sequences.…”

“…A follow-up fMRI study using identical tasks and implicit instructions showed that, compared with the Control SRT task, the cerebellar Crus I was recruited during learning a sequence of beliefs (during Training) and detecting disruptions of this sequence (during Test), whereas the Crus II was activated when this belief sequence continued, but with occasional sequence disruptions (during Test; Ma, Pu, et al, 2021b). The temporoparietal junction (TPJ) also was activated when participants were inferring the protagonists' beliefs during initial learning of the standard sequence and detecting disruptions of it.…”

“…However, a recent study that included social contexts revealed impaired performance even when cerebellar patients were explicitly asked to give correct orders of stories requiring the understanding of other's beliefs, while they performed at normal levels for routine social or physical events (Van Overwalle, De Coninck, et al, 2019a). These findings raise two pivotal questions: (1) Given that the posterior cerebellum is preferentially involved in implicit learning of social sequences as demonstrated by Ma, Pu, et al (2021b), does it also contribute to explicit social learning? (2) Is there a difference between explicit and implicit sequence learning in a social context?…”

“…To address the second question whether explicit and implicit social sequence learning differ, we compared the current explicit Belief SRT task to the previous implicit Belief SRT task (Ma, Pu, et al, 2021b). Because clinical studies have suggested stronger cerebellar involvement during implicit, rather than explicit, sequence learning (Morgan et al, 2020;Taylor et al, 2010), we hypothesized that, compared with the implicit Belief SRT task, the present explicit Belief SRT task may recruit less activation in the posterior cerebellar Crus, because the cerebellum is more engaged in implicit learning.…”