Role of the Contralesional Hemisphere in Post-Stroke Recovery of Upper Extremity Motor Function

Abstract

Identification of optimal treatment strategies to improve recovery is limited by the incomplete understanding of the neurobiological principles of recovery. Motor cortex (M1) reorganization of the lesioned hemisphere (ipsilesional M1) plays a major role in post-stroke motor recovery and is a primary target for rehabilitation therapy. Reorganization of M1 in the hemisphere contralateral to the stroke (contralesional M1) may, however, serve as an additional source of cortical reorganization and related recovery. The extent and outcome of such reorganization depends on many factors, including lesion size and time since stroke. In the chronic phase post-stroke, contralesional M1 seems to interfere with motor function of the paretic limb in a subset of patients, possibly through abnormally increased inhibition of lesioned M1 by the contralesional M1. In such patients, decreasing contralesional M1 excitability by cortical stimulation results in improved performance of the paretic limb. However, emerging evidence suggests a potentially supportive role of contralesional M1. After infarction of M1 or its corticospinal projections, there is abnormally increased excitatory neural activity and activation in contralesional M1 that correlates with favorable motor recovery. Decreasing contralesional M1 excitability in these patients may result in deterioration of paretic limb performance. In animal stroke models, reorganizational changes in contralesional M1 depend on the lesion size and rehabilitation treatment and include long-term changes in neurotransmitter systems, dendritic growth, and synapse formation. While there is, therefore, some evidence that activity in contralesional M1 will impact the extent of motor function of the paretic limb in the subacute and chronic phase post-stroke and may serve as a new target for rehabilitation treatment strategies, the precise factors that specifically influence its role in the recovery process remain to be defined.

Spontaneous and Therapeutic-Induced Mechanisms of Functional Recovery After Stroke

“…The utility of these distributed networks in post-stroke recovery is dependent on the amount of clinical impairment, the extent of injury, and the complexity of the functional task. The contralesional hemisphere is a particularly controversial area under study [75] especially in the context of upper-extremity motor recovery (detailed review by Buetefisch, 2015) [76]. Numerous studies support the role of the contralesional hemisphere in recovery of the stroke-affected upper-extremity [43, 41, 77–80].…”

Brain‐computer interfaces for post‐stroke motor rehabilitation: a meta‐analysis

“…Although the role of the unaffected hemisphere in poststroke recovery is unclear, the ipsilesional primary motor cortex is thought to play a major role in motor recovery. Typical BCI‐based motor rehabilitation protocols have predominantly aimed at cortical reorganization of the lesioned hemisphere 27. Specifically, most BCI‐based motor rehabilitation systems have traditionally encompassed neural activity decoders of ipsilesional sensorimotor activity (sensorimotor rhythm, SMR, 9–15 Hz).…”

Preclinical and Clinical Evidence on Ipsilateral Corticospinal Projections: Implication for Motor Recovery

“…The aim of this manuscript is to review the neuroanatomical trajectory and functional relevance of iCST fibers in mammalian species, including human, and how these findings are implicated in neurorehabilitation after brain injury, mainly in the context of cerebral palsy and stroke. It is necessary to emphasize that discussing the role of the ipsilateral hemisphere in recovery from stroke is beyond the scope of this review and has been extensively reviewed [10, 11]. …”