A New Framework to Interpret Individual Inter-Hemispheric Compensatory Communication after Stroke

Abstract

Stroke constitutes the main cause of adult disability worldwide. Even after application of standard rehabilitation protocols, the majority of patients still show relevant motor impairment. Outcomes of standard rehabilitation protocols have led to mixed results, suggesting that relevant factors for brain re-organization after stroke have not been considered in explanatory models. Therefore, finding a comprehensive model to optimally define patient-dependent rehabilitation protocols represents a crucial topic in clinical neuroscience. In this context, we first report on the rehabilitation models conceived thus far in the attempt of predicting stroke rehabilitation outcomes. Then, we propose a new framework to interpret results in stroke literature in the light of the latest evidence regarding: (1) the role of the callosum in inter-hemispheric communication, (2) the role of prefrontal cortices in exerting a control function, and (3) diaschisis mechanisms. These new pieces of evidence on the role of callosum can help to understand which compensatory mechanism may take place following a stroke. Moreover, depending on the individual impairment, the prefrontal control network will play different roles according to the need of high-level motor control. We believe that our new model, which includes crucial overlooked factors, will enable clinicians to better define individualized motor rehabilitation protocols.

Brain State-dependent Repetitive Transcranial Magnetic Stimulation for Motor Stroke Rehabilitation: A Proof of Concept Randomized Controlled Trial

“…Indeed, the IHI imbalance model itself is currently being debated and re-evaluated in light of recent evidence [43][44][45][46][47] , suggesting that IHI per se should not be a target for rTMS interventions 46 . Contemporary models of interhemispheric communication present a more complex picture of the interaction between the two hemispheres following stroke, contingent on factors such as structural reserve 48 and integrity of the callosal and frontal connections 49 . It is crucial to emphasize, however, that the ongoing debate around the IHI model does not invalidate previously reported beneficial effects (for an overview, see: Kim et al (2020), and Starosta et al ( 2022)) 50,51 .…”

Functional Connectivity States of Alpha Rhythm Sources in the Human Cortex at Rest: Implications for Real-Time Brain State Dependent EEG-TMS

“…This new perspective would also be useful for developing new and more effective individualized approaches for rehabilitation via brain-state dependent stimulation. In this regard, individualized stimulation rehabilitative protocols have been proposed in stroke patients for whom specific adaptive connectivity patterns between specific cortical regions should be reinforced in order to achieve recovery [40]. In this light, our approach combining brain-state dependent stimulation with phase-dependent connectivity measures would nicely suit this purpose.…”

Improving visual attention following right hemisphere stroke: A preliminary study

“…Comparably in the motor domain, less severe unilateral stroke patients with preserved corpus callosum recover motor functions better than more impaired patients. The unaffected hemisphere plays a crucial role in recovery by interhemispheric cross-facilitation of functions as evidenced by behavioral tasks (Carson 2020; Brancaccio et al, 2022). Similarly, our novel experimental protocol to promote recovery by isolating attention in the ipsilesional field might have boosted bilateral improvement in the less severe cases of leftward inattention, thanks in part to preserved structures in the left hemisphere.…”