Brain Dynamics of Action Monitoring in Higher-Order Motor Control Disorders: The Case of Apraxia

Neuromodulation of the Left Inferior Frontal Cortex Affects Social Monitoring during Motor Interactions

Motor interactions require observing and monitoring a partner's performance as the interaction unfolds. Studies in monkeys suggest that this form of social monitoring might be mediated by the activity of the ventral premotor cortex (vPMc), a critical brain region in action observation and motor planning. Our previous fMRI studies in humans showed that the left vPMc is indeed recruited during social monitoring, but its causal role is unexplored. In three experiments, we applied online anodal or cathodal transcranial direct current stimulation over the left lateral frontal cortex during a music-like interactive task to test the hypothesis that neuromodulation of the left vPMc affects participants' performance when a partner violates the agent's expectations. Participants played short musical sequences together with a virtual partner by playing one note each in turn-taking. In 50% of the trials, the partner violated the participant's expectations by generating the correct note through an unexpected movement. During sham stimulation, the partner's unexpected behavior led to a slowdown in the participant's performance (observation-induced posterror slowing). A significant interaction with the stimulation type showed that cathodal and anodal transcranial direct current stimulation induced modulation of the observation-induced posterror slowing in opposite directions by reducing or enhancing it, respectively. Cathodal stimulation significantly reduced the effect compared to sham stimulation. No effect of neuromodulation was found when the partner behaved as expected or when the observed violation occurred within a context that was perceptually matched but noninteractive in nature. These results provide evidence for the critical causal role that the left vPMc might play in social monitoring during motor interactions, possibly through the interplay with other brain regions in the posterior medial frontal cortex.

The Impact of Upper Limb Apraxia on General and Domain-Specific Self-Efficacy in Post-Stroke Patients

BACKGROUND

Upper limb apraxia (ULA) is a neurological syndrome characterized by the inability to perform purposeful movements. ULA could impact individuals' perceptions, including perceived self-efficacy. The aim of this study is to investigate whether ULA is related to general self-efficacy and self-efficacy for managing symptoms in post-stroke patients.

METHODS

A cross-sectional study was conducted involving 82 post-stroke patients. Regression analyses were implemented using a stepwise model including seven dimensions of ULA: imitation (non-symbolic, intransitive, and transitive), pantomime (non-symbolic, intransitive, and transitive), and dimension of apraxic performance in activities of daily living. These dimensions were independent variables, while general self-efficacy and symptom management self-efficacy dimensions were dependent variables.

RESULTS

The findings revealed that intransitive imitation accounted for 14% of the variance in general self-efficacy and 10% of self-efficacy for managing emotional symptoms. Transitive imitation explained 10% of the variance in self-efficacy for managing global symptoms and 5% for social-home integration symptoms. The combination of intransitive imitation, non-symbolic pantomime, and alterations in activities of daily living performance associated with ULA explained 24% of the variance in cognitive self-efficacy.

CONCLUSIONS

Hence, ULA dimensions seem to be related to the levels of general perceived self-efficacy and self-efficacy for managing symptoms among post-stroke patients.

Combined EEG and immersive virtual reality unveil dopaminergic modulation of error monitoring in Parkinson's Disease

Detecting errors in your own and others' actions is associated with discrepancies between intended and expected outcomes. The processing of salient events is associated with dopamine release, the balance of which is altered in Parkinson's disease (PD). Errors in observed actions trigger various electrocortical indices (e.g. mid-frontal theta, error-related delta, and error positivity [oPe]). However, the impact of dopamine depletion to observed errors in the same individual remains unclear. Healthy controls (HCs) and PD patients observed ecological reach-to-grasp-a-glass actions performed by a virtual arm from a first-person perspective. PD patients were tested under their dopaminergic medication (on-condition) and after dopaminergic withdrawal (off-condition). Analyses of oPe, delta, and theta-power increases indicate that while the formers were elicited after incorrect vs. correct actions in all groups, the latter were observed in on-condition but altered in off-condition PD. Therefore, different EEG error signatures may index the activity of distinct mechanisms, and error-related theta power is selectively modulated by dopamine depletion. Our findings may facilitate discovering dopamine-related biomarkers for error-monitoring dysfunctions that may have crucial theoretical and clinical implications.