Noninvasive cerebellar stimulation and behavioral interventions: A crucial synergy for post-stroke motor rehabilitation.

BACKGROUND: Improvement of functional movements after supratentorial stroke occurs through spontaneous biological recovery and training-induced reorganization of remnant neural networks. The cerebellum, through its connectivity with the cortex, brainstem and spinal cord, is actively engaged in both recovery and reorganization processes within the cognitive and sensorimotor systems. Noninvasive cerebellar stimulation (NiCBS) offers a safe, clinically feasible and potentially effective way to modulate the excitability of spared neural networks and promote movement recovery after supratentorial stroke. NiCBS modulates cerebellar connectivity to the cerebral cortex and brainstem, as well as influences the sensorimotor and frontoparietal networks. OBJECTIVE: Our objective was twofold: (a) to conduct a scoping review of studies that employed NiCBS to influence motor recovery and learning in individuals with stroke, and (b) to present a theory-driven framework to inform the use of NiCBS to target distinct stroke-related deficits. METHODS: A scoping review of current research up to August 2023 was conducted to determine the effect size of NiCBS effect on movement recovery of upper extremity function, balance, walking and motor learning in humans with stroke. RESULTS: Calculated effect sizes were moderate to high, offering promise for improving upper extremity, balance and walking outcomes after stroke. We present a conceptual framework that capitalizes on cognitive-motor specialization of the cerebellum to formulate a synergy between NiCBS and behavioral interventions to target specific movement deficits. CONCLUSION: NiCBS enhances recovery of upper extremity impairments, balance and walking after stroke. Physiologically-informed synergies between NiCBS and behavioral interventions have the potential to enhance recovery. Finally, we propose future directions in neurophysiological, behavioral, and clinical research to move NiCBS through the translational pipeline and augment motor recovery after stroke.

Goal conceptualization has distinct effects on spatial and temporal bimanual coordination after left- and right- hemisphere stroke.

Perception of task goal influences motor performance and coordination. In bimanual actions, it is unclear how one's perception of task goals influences bimanual coordination and performance in individuals with unilateral stroke. We characterized inter-limb coordination differences in individuals with chronic right- and left-hemisphere damaged (RCVA: n = 24, LCVA: n = 24) stroke and age-matched neurotypical controls (n = 24) as they completed bimanual reaching tasks under distinct goal conditions. In the dual-goal condition, participants reached to move two virtual bricks (cursors) assigned to each hand toward independent targets. In the common-goal condition, they moved a central common virtual brick representing both hands to a single, central target. Spatial and temporal coordination (cross-correlation coefficients of hand velocity and their time-lag), the redundant axis deviations (the hand deviations in the axis orthogonal to the axis along the cursor-target direction), and the contribution ratio of the paretic hand were measured. Compared to the dual-goal condition, reaching actions to the common-goal demonstrated better spatial bimanual coordination in all three participant groups. Temporal coordination was better during common-goal than dual-goal actions only for the LCVA group. Additionally, and novel to this field, sex, as a biological variable, differently influenced movement time and redundant axis deviation in participants with stroke under the common-goal condition. Specifically, female stroke survivors showed larger movements in the redundant axes and, consequently, longer movement times, which was more prominent in the LCVA group. Our results indicate that perception of task goals influences bimanual coordination, with common goal improving spatial coordination in neurotypical individuals and individuals with unilateral stroke and providing additional advantage for temporal coordination in those with LCVA. Sex influences bimanual performance in stroke survivors and needs to be considered in future investigations.