Kris Baetens

An increasing number of studies have revealed that the posterior cerebellum plays a vital role in mentalizing by identifying and learning social action seq

Background: Implicit motor sequence learning (IMSL), the incidental acquisition of sequential motor skills without conscious awareness, underlies many daily functional activities. Anodal transcranial direct-current stimulation (tDCS) over the primary motor cortex (M1) has been proposed to facilitate IMSL, but evidence is mixed and cumulative effects of repeated stimulation across acquisition, consolidation, and retention remain poorly characterized.Methods: In a double-blind, sham-controlled, between-subjects design, 60 healthy young adults received 2 mA anodal tDCS or sham over M1 concurrently with serial reaction time task (SRTT) performance across three consecutive training sessions separated by 24-hour intervals, with retention assessed one week later. Sequence-specific (SSLE; primary) and general learning effects (GLE; secondary) were analyzed using linear mixed-effects models.Results: Anodal tDCS did not modulate SSLE during training (Sessions 1–3; all p’s > .30). At follow-up, SSLE was significantly reduced in the anodal group relative to sham (p < .0001), driven by lower random-block response times against equivalent, floor-level performance in sequential blocks. GLE was unaffected during training, and accuracy remained near ceiling throughout.Conclusion: Repeated anodal M1 tDCS did not facilitate IMSL during training. The follow-up SSLE reduction is most parsimoniously attributed to general motor speed facilitation rather than stimulation-specific modulation of sequential retention, with floor-level sequential performance precluding firm conclusions about sequence-specific effects. These findings challenge the reliability of M1 tDCS for modulating IMSL in healthy young adults. Importantly, null findings in healthy populations do not preclude meaningful effects in neurologically impaired systems where sensitivity to excitability changes may be more substantial.

Prior research in clinical eating disorder populations suggests that altered inhibition-underactive and overactive-contribute to overeating/purging and restrictive eating, respectively. However, it remains unclear whether these alterations manifest at non-clinical levels, which is particularly important from a preventive perspective. Currently, research in non-clinical DEBs is fairly limited, generally relying on small samples and restrictive DEB. This study examined behavioral (reactive and proactive) and dispositional (Behavioral Approach/Inhibition Systems (BIS/BAS), Effortful Control (EC)) measures of inhibition among different non-clinical DEBs in a large sample of adults (N = 425), classified into a restrictive (n = 80), binge-eating/purging (n = 173), and comparison (n = 172) group. Participants completed two inhibition tasks (Stop-Signal Task, Go/NoGo Task) and self-report questionnaires (BIS/BAS scales, EC scale). Results revealed that individuals with restrictive DEB exhibited increased proactive inhibition, whereas no significant differences were observed for reactive inhibition. No behavioral differences were found for the binge-eating/purging group, though they reported lower self-reported EC. Elevated BIS levels were observed in both DEB groups relative to comparisons. These findings provide preliminary support for inhibitory alterations among non-clinical DEBs and highlight the potential utility of assessing and targeting inhibitory processes in future longitudinal research as part of a broader preventive framework for DEBs.

This dynamic causal modeling (DCM) analysis, comprising 99 participants from 4 studies, investigated effective neuronal connectivity during social action sequence prediction. The analysis focused on mentalizing areas within the cerebellum, specifically the bilateral Crus 1, Crus 2, and lobule IX, as well as cerebral mentalizing areas within the precuneus, temporo-parietal junction (TPJ), and dorsal medial prefrontal cortex (dmPFC). Consistent with previous research, we found robust bidirectional closed loop connections between the posterior cerebellar Crus and cerebral mentalizing areas. We also found previously unexplored unidirectional connections originating from cerebellar lobule IX to the dmPFC and left TPJ and from the right TPJ to lobule IX. Furthermore, we uncovered many bidirectional closed loops within the cerebellum between the left and right Crus 1, and between Crus 1 and Crus 2, and for the first time, between the bilateral Crus 2 and lobule IX. Our findings illuminate the distinct role of cerebellar Crus and lobule IX, and cerebral mentalizing areas in predicting social action sequences.

Social navigation involves observing individuals navigating a socially rich environment sequentially while mentalizing their goals or preferences. The posterior cerebellum plays a central role in regulating human social behaviour and guiding social navigation. However, the extent to which cerebello-cerebral pathways mediate this role has not been sufficiently studied. Using Dynamic Causal Modelling on four novel social navigation studies (N = 107), our results showed many bidirectional connections between cerebellar Crus 2 and cortical mentalizing areas, including the temporoparietal junction, precuneus, and medial prefrontal cortex (mPFC), spanning both ipsilaterally and contralaterally. Connectivity patterns were only slightly modulated by experimental manipulations involving (i) active encoding versus passive observation of navigational sequences and (ii) social versus non-social sequences. Furthermore, when participants observed behaviours defying social expectations or norms, upward connectivity from the right Crus 2 to the ventral mPFC and downward connectivity from the precuneus to the left Crus 2 became stronger, while upward connectivity from the left Crus 2 to the ventral mPFC weakened. This study enhances our understanding of the role of the cerebellum in effective connectivity and its changes in response to social violations during social navigation.