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.

IntroductionSocial categorization is a fundamental aspect of social perception, enabling individuals to process vast amounts of information efficiently. This exploratory fMRI study investigated whether different types of social groups are represented in the brain as stable memory representations.MethodsWe used repetition suppression as a proxy-measurement for such stable representation, examining four groups categorized by their warmth and competence into the quadrants of the Stereotype Content Model (SCM). Participants judged the typicality of behavioral sentences associated with these groups, presented in pairs that either repeated the same group, or not.ResultsA repetition suppression pattern was observed in the posterior temporal sulcus (pSTS) for groups with mixed warmth and competence; specifically the rich (low warmth, high competence) and the poor (high warmth, low competence). By contrast, no suppression was detected for non-mixed groups (military people and welfare recipients).DiscussionWe theorize that mixed groups elicit greater ambiguity, which may prompt the brain to form more robust representations to quickly assess their functional relevance. These findings suggest that stable group representations are not uniformly applied across all group types and may reflect social complexity and motivational salience. The results highlight the pSTS as a key node in group representation and invite further research into its functional role.

Casto et al.1 carried out an extensive investigation demonstrating the involvement of the cerebellum in linguistic processing and identified a language-specialized area located mainly in posterior Crus I/II. The study offers an analysis of the cerebellum’s contribution to language at the level of words and sentences, in comparison with numerous other cognitive and social domains and in relation to the neocortical language network.

INTRODUCTION:Implicit motor sequence learning (IMSL) enables unconscious acquisition of everyday motor skills and involves stage-specific neural dynamics. Beta-band (13-30 Hz) activity is believed to support consolidation, yet its causal role across IMSL stages remains unclear. METHODS:We conducted the first study examining the effects of repeated 20 Hz transcranial alternating current stimulation (tACS) over the motor cortex on IMSL acquisition, consolidation and retention. Using a double-blind, sham-controlled, between-subjects design, 80 healthy young adults received active or sham tACS during a serial reaction time task (SRTT) across three consecutive days (Sessions 1-3), with retention assessed one week later (Follow-Up). RESULTS:Mixed-effects models revealed sequence-specific learning in both groups, across sessions (all p's < .0001). Active tACS tended to enhance learning in Session 1 (M = 54.62 ms) vs. sham (M = 41.89 ms), p = .063, but significantly impaired learning in Session 2 (active M = 75.97 ms, sham M = 85.95 ms, p = .003), Session 3 (active M = 95.89 ms, sham M = 113.14 ms, p < .0001), and at Follow-Up (active M = 91.79 ms, sham M = 117.21 ms, p < .0001). CONCLUSION:Repeated beta-tACS tended to improve acquisition, but impaired consolidation and retention. This stage-specific disruption - preserved early learning followed by later deficits - supports a dynamic role for beta oscillations: early desynchronization facilitates flexible encoding, while later synchronization stabilizes learned patterns. Recovery during random blocks suggests transient disruption of motor flexibility followed by compensatory adaptation, rather than premature overgeneralization of sequence knowledge.

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.

Despite its importance, sequence learning has been mostly studied in the visuo-motor domain and its neural underpinnings are debated. Here, we present a novel coordinate-based meta-analysis of brain areas involved in deterministic sequence learning across social mentalizing, cognitive, visuo-motor and motor domains, under both implicit and explicit conditions, focusing primarily on acquisition. The analysis revealed a central network including frontal areas, cerebellum, and basal ganglia, with domain-specific specializations. At the cortical level, the medial prefrontal cortex appears to be specifically involved in the sequential order of social inputs that support and elicit representation of others’ mental states. In addition, the primary motor cortex is more engaged during motor-only tasks to ensure accurate motor sequential action execution, while the premotor cortex and the superior parietal areas are particularly active during visuo-motor sequence tasks likely supporting visuo-motor integration. Within subcortical regions, a functional gradient was observed in the cerebellum along the anterior to posterior axis, while the basal ganglia showed a functional specialization from lateral to medial regions, both reflecting a shift from motor-only and visuo-motor processing to more complex cognitive and social functions. The different domains highlight distinct integrated functional circuits involving the sensorimotor, ventral/dorsal attention and mentalizing/default mode networks. Within the visuo-motor domain, at the subcortical level, implicit learning relies on basal ganglia, while explicit learning involves the cerebellum. The cerebellum may contribute to the early acquisition stage in implicit learning, though evidence remains limited. This study shows how the brain shapes sequence learning, crucial for motor and social-cognitive behavior.

Friedreich ataxia (FA) is a cerebellar neurodegenerative disease primarily known for its motor symptoms, but emerging evidence suggests it also affects higher-order cognitive functions, including Theory of Mind (ToM). This study aimed to assess ToM in individuals with FA using a Picture Sequencing Task (PST) that distinguishes between mechanical, social script, true belief, and false belief scenarios, with a focus on the latter as key marker of mentalizing in cerebellar diseases. Twenty-three FA patients and age- and sex-matched healthy controls completed the PST. Accuracy and normalized reaction times were compared between groups. Correlations between task performance and clinical severity (SARA score) were analyzed within the FA group. P values were adjusted for false discovery rates (p-FDR) using the Benjamini Hochberg method. FA patients showed significantly lower accuracy in the false belief condition (p-FDR = 0.03) and a reduced global accuracy score (p-FDR = 0.03), while other conditions showed no group differences. Accuracy in false belief trials negatively correlated with disease severity (ρ = − 0.482, p-FDR = 0.04). Normalized reaction times did not differ between groups, suggesting preserved processing speed when accounting for motor slowness. Our results reveal a selective impairment in false belief reasoning in FA, consistent with ToM deficits observed in other cerebellar and neurodevelopmental disorders. Not applicable.

The cerebellum has been increasingly recognized for its role in social cognition, particularly in mentalizing processes. A way to measure mentalizing is the picture sequencing task, a well-established measure of social action sequencing during mentalizing of other’s beliefs. Recent studies have shown that cerebellar transcranial direct current stimulation can affect social sequence processing in adults, however, the effects of different types of stimulation remain unclear. Therefore, in this study, we examined the effects of a novel and more focal montage of cerebellar tDCS on the picture sequencing task in healthy adults. Using a within-participant design, 35 participants completed three sessions in which they underwent anodal, cathodal, and sham stimulation (in a counterbalanced order). Results revealed that participants were consistently slower on sequences that required complex mentalizing compared to well-known social situations and non-social events. Anodal tDCS significantly speeded up reaction times from the second session (indicating an improvement in performance), sham tDCS showed the same improvement in the third session (indicating general improved familiarity with the task), while cathodal tDCS did not change performance. This interaction between stimulation type and session suggests that anodal tDCS may accelerate sequence learning, while cathodal tDCS may inhibit it. Accuracy results reflected a similar pattern, with improvements over time driven by the stimulation-learning interaction. In conclusion, cerebellar tDCS modulates performance with anodal stimulation enhancing processing speed and learning. More importantly, the interaction between the different types of stimulation and learning reinforces the importance of the cerebellum in social learning processes.

Traditional approaches to studying perceptual sequence learning (SL) often employ adaptations of the classical serial reaction time task, albeit these tasks suffer from confounding factors such as (oculo)motor learning effects. Unlike motor SL, the extent to which pure perceptual SL can occur implicitly without (oculo)motor learning remains uncertain. We adapted a previously formulated task (Garvert et al., eLife, 6, 1–20, 2017) to isolate perceptual sequence learning, without the interference of (oculo)motor confounds, and to determine whether perceptual sequence learning can occur implicitly. Fifty participants judged whether each object appeared in its original or mirrored form, gradually improving performance based on feedback. Unbeknownst to participants, the succession of these objects followed a probabilistic sequence. A training phase consisting of 8 regular blocks was followed by a testing phase, where 5 random and 5 regular blocks were presented alternatingly. A force-choice recognition test probing knowledge about specific transitions in the task was also used to assess explicit knowledge. Our findings indicate robust perceptual SL effects, as indicated by slower reaction times (RTs) in random blocks than regular blocks. Notably, transitions between objects with higher communicability (i.e., a metric of objects’ connectedness within the underlying grid) showed lower RTs in regular, but not random blocks. This indicates that perceptual SL in our task may rely on strategic cognitive processes in response to violations of expectation. Importantly, our results also demonstrate that explicit knowledge of the underlying structure did not influence perceptual SL in any way, suggesting that learning was driven by implicit knowledge.

Purpose:This research investigated implicit social sequencing in adults with Autism Spectrum Disorder. Previous research emphasized the role of the cerebellum in autism, and in processing action sequences within social contexts requiring mental state attribution (mentalizing). We therefore hypothesized that individuals with autism would show reduced implicit sequencing in an interactive negotiation game that involves mentalizing. Methods:Participants included 20 adults with autism and 20 matched healthy controls. Using a novel ultimatum serial reaction time task, participants received offers for a division of 10 points from multiple proposers and responded as quickly as possible. Unbeknownst to the participants, offers were presented in repeated or random sequences. Additionally, the proposers' implied traits (egocentric versus generous offers) and the volatility of their offers (variable versus stable) were varied to assess context effects on implicit sequencing. Results:As expected, autistic participants revealed no significant speed differences between repeated and random sequences, while controls were faster in repeated sequences. Considering context effects, both groups were faster in repeated sequences when offers were stable (i.e., identical across trials). Conversely, when offers were volatile, responses slowed down under repeated sequences. Conclusion:Findings suggest reduced implicit social sequencing capacities in adults with autism. Social context factors influenced learning in both groups, indicating that autistic individuals may either perform at typical social levels when statistically controlling for their reduced sequencing capacities, or may sufficiently compensate under explicit task instructions. These results highlight social sequence learning as a promising target for intervention in training programs for autistic individuals.

Balgova et al. (2024) recently conducted a large-scale meta-analysis on mentalizing and on semantic cognition, to investigate the degree to which the neural correlates of these two processes are overlapping. The study found consistent neural overlap between the two processes, especially in the bilateral anterior temporal lobe (ATL) and the left temporoparietal junction (TPJ), although they also identified many areas of activation specific to mentalizing. Although we agree with their general conclusion, we investigated to what extent the semantic dataset was actually devoid of social content, and if not, how this would change the results. After careful screening and categorization of the “semantic” material, we found experiments that contained elements of social mentalizing (N = 36) and social action observation (N = 16), apart from nonsocial semantics (N = 46). ALE analyses on the social mentalizing and nonsocial semantic subsets from the original “semantic” full dataset, confirmed that semantic brain areas are activated when processing both social mentalizing and nonsocial semantic content, while mentalizing brain areas are uniquely activated when processing social mentalizing content. Specifically, semantic and mentalizing content activated the left inferior frontal gyrus (IFG), left middle temporal gyrus (MTG) and posterior medial frontal cortex (pmFC); and also the left ventral temporal lobe, supporting the graded multimodal hub model of semantic cognition. Critically, as we claimed, mentalizing content uniquely activated the temporal pole (TP), medial prefrontal cortex (mPFC), although activation in the left TPJ was also shared with semantic processes. We conclude that a more careful distinction between social and nonsocial datasets guarantees more sensitive and valid analyses.

There is accumulating evidence that the human cerebellum is heavily implicated in adult social cognition. Yet, its involvement in the development of Theory of Mind (ToM), a hallmark of social cognition, remains elusive. Using openly available functional MRI data of children with emerging ToM abilities (N = 41, age range: 3-12 years) and adults (N = 78), we show that children who pass a false-belief assessment of ToM abilities activate cerebellar Crus I-II in response to ToM events during a movie-watching task, similar to adults. This activation is not statistically significant in children who do not pass the ToM assessment. Functional connectivity profiles between cerebellar and cerebral ToM regions differ as a function of children's ToM abilities. Notably, task-driven connectivity shifts from upstream to downstream connections between cerebellar and cerebral ToM regions from childhood to adulthood. Greater dependence on connections emerging from the cerebellum early in life suggests an important role of the cerebellum in establishing the cognitive processes underlying ToM in childhood and thus for the undisrupted development of social cognition.

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.

Many studies have explored the neural correlates and benefits of mindfulness, but have rarely focused on its components. This neuroimaging study investigates two components of a short mindfulness training, namely interoception and mindful attention, compared to immersion as an active control condition. Healthy participants were trained in three conditions: (1) interoception, (2) mindful attention of bodily sensations, and (3) immersion. In the scanner, participants read and imagined stressful self-relevant events while adopting one of these three strategies and rated subjective arousal. Participants felt the least aroused in the mindful attention condition compared to both immersion and interoception. Compared to immersion, interoception decreased activation in regions of the Default Mode Network (DMN), including the anterior cingulate cortex (ACC)/medial prefrontal cortex (mPFC), precuneus, angular gyrus, and hippocampus, while mindful attention increased activation in regions related to the sensation of bodily states, such as the bilateral insula. Although the results broadly align with prior research, we argue that inconsistent past findings concerning the amygdala and insula activation might be due to a differential focus on mindfulness components. We discuss other explanations for our results, including differences in prior mindfulness experience.

ABSTRACT Purpose The cerebellum's role extends beyond motor control, impacting various cognitive functions. A growing body of evidence supports the idea that the cerebellum optimizes performance across cognitive domains, suggesting critical connectivity with the neocortex. This study investigates how cerebellar transcranial direct current stimulation (tDCS) targeting the right Crus II region modulates functional brain connectivity. Method Using a within‐subject design, 21 healthy participants underwent both sham and anodal cerebellar tDCS at 2 mA during 20 min of concurrent resting‐state fMRI sessions. Data was preprocessed, and connectivity changes were examined using seed‐to‐voxel analysis. Given the potential impact of cerebellar dysfunctions on symptoms associated with autism spectrum disorders, we also assessed how individual autism quotient (AQ) scores might influence cerebellar functional connectivity. Moreover, electrical field simulations were computed for each participant to explore the effects of individual differences. Findings Results indicated increased functional connectivity between the cerebellar Crus II and the right inferior frontal gyrus (IFG) during active tDCS compared to sham stimulation. The IFG (part of the Action Observation Network) plays a crucial role in understanding the actions and intentions of others, implicating the cerebellum in higher‐order cognitive processes. In addition, linear mixed‐effects models revealed an interaction between electric field strength and AQ scores, suggesting that functional connectivity changes are based on individual psychobiological differences. Conclusion Cerebellar tDCS significantly altered functional brain connectivity, particularly between the cerebellar Crus II and the IFG, both involved in social cognition. These findings contribute to our understanding of the cerebellum's role beyond motor control, highlighting its impact on cognitive and social processes and its potential for therapeutic applications, such as autism spectrum disorders.

The present meta-analysis investigated the impact of non-invasive stimulation, using transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS) targeting the posterior cerebellum, on social and emotional mentalizing about others. Prior research has convincingly shown that the posterior cerebellum supports social and emotional cognition. We identified 14 studies targeting the cerebellum with appropriate control conditions (i.e., sham, control site), which exclude general learning effects of the task or placebo effects. The studies included 29 task conditions where stimulation before or during a social or emotional task was applied on healthy samples. The results showed significant evidence that sustained anodal tDCS and TMS generally improved social and emotional performance after stimulation, in comparison with sham or control conditions, with a small effect size. In contrast, cathodal stimulation showed mixed facilitatory and inhibitory results. In addition, short TMS pulses, administered with the aim of interfering with ongoing social or emotional processes, induced a small but consistent inhibitory effect. Control tasks without social or emotional components also showed significant improvement after sustained anodal tDCS and TMS, suggesting that transcranial stimulation of the cerebellum may also improve other functions. This was not the case for short TMS pulses, which did not modulate non-social and non-emotional control tasks. Taken together, this meta-analysis shows that cerebellar neurostimulation confirms a causal role of the cerebellum in socio-emotional cognition, has a small but significant effect on improving socio-emotional skills, and may, therefore, have important clinical applications in pathologies where social and emotional cognition is impaired.

Implicit motor sequence learning (IMSL) is a cognitive function that is known to be directly associated with impaired motor function in Parkinson's disease (PD). Research on healthy young participants shows the potential for transcranial direct current stimulation (tDCS), a noninvasive brain stimulation technique, over the primary motor cortex (M1) to enhance IMSL. tDCS has direct effects on the underlying cortex, but also induces distant (basal ganglia) network effects—hence its potential value in PD, a prime model of basal ganglia dysfunction. To date, only null effects have been reported in persons with PD. However, these studies did not determine the reacquisition effects, although previous studies in healthy young adults suggest that tDCS specifically exerts its beneficial effects on IMSL on reacquisition rather than acquisition. In the current study, we will therefore establish possible reacquisition effects, which are of a particular interest, as long‐term effects are vital for the successful functional rehabilitation of persons with PD. Using a sham‐controlled, counterbalanced design, we will investigate the potential of tDCS delivered over M1 to enhance IMSL, as measured by the serial reaction time task, in persons with PD and a neurologically healthy age‐ and sex‐matched control (HC) group. Multilevel Mixed Models will be implemented to analyze the sequence‐specific aspect of IMSL (primary outcome) and general learning (secondary outcome). We will determine not only the immediate effects that may occur concurrently with the application of tDCS but also the short‐term (5 min post‐tDCS) and long‐term (1 week post‐tDCS) reacquisition effects.

The posterior cerebellum and anterior basal ganglia are critical subcortical structures for learning and identifying dynamic action sequences, in concert with the neocortex. The present analysis investigates the role of action sequences during social mentalizing, termed here dynamic or sequential social mentalizing. Although the role of the cerebellum in dynamic social mentalizing was extensively investigated during the last decade, the basal ganglia were long ignored. We conducted an activation likelihood estimation coordinate-based meta-analysis of sequential social mentalizing tasks (with 485 participants in 17 studies). These tasks required participants to make social mentalizing inferences ranging from low-level goals to high-level beliefs and traits, while either memorizing, generating or predicting temporal sequences of the social actions involved (i.e., social sequencing condition), or not (i.e., social non-sequencing control condition), or did so for nonsocial objects (i.e., nonsocial sequencing control condition). The tasks also occasionally included inconsistencies in social behavior. Results revealed that the cerebellum exhibited a preference for social, sequencing, and inconsistent information, while the basal ganglia showed a preference for sequencing and inconsistency, without a general preference for social input. Meta-analytic connectivity analysis further showed evidence of coactivation between mentalizing areas of the cerebellum, basal ganglia and cerebral neocortex. The present work underscores the role of subcortical structures in social mentalizing about dynamic action sequences.