8. Evolution and recovery of motor function post-stroke

Abstract

Background and Objectives With the advent of novel neuromodulatory interventions in post-stroke recovery, the evolution of intracortical excitability changes, particularly those over the contralesional hemisphere following stroke, and their relevance to functional recovery requires further clarification. As such, the present study utilized a prospective longitudinal design over an 18-month period from stroke onset, to investigate the evolution of intracortical excitability over both motor cortices and their relation to functional recovery. Methods A total of thirty-three acute stroke patients and 29 control subjects were recruited in the study. Paired-pulse transcranial magnetic stimulation and comprehensive clinical assessments were undertaken at stroke onset and then repeated at 3-, 6-, 12-, and 18-months follow-up. Results Immediately after stroke, short-interval intracortical inhibition (SICI) was significantly reduced in both hemispheres compared with controls that correlated with the degree of functional improvement over the first 3-months. Over the follow-up period, ipsilesional SICI remained reduced in all patient groups, whilst SICI over the contralesional hemisphere remained suppressed only in the groups with cortical stroke and more severe baseline functional impairment. Furthermore, contralesional SICI was more reduced in these groups of patients compared to those with subcortical stroke location and milder baseline impairment during the longitudinal assessment period. Clinical scores demonstrated improvement over this period with the most significant changes occurring in the first 3-months. Conclusion Intracortical disinhibition occurs in both hemispheres immediately following acute stroke that likely represent functionally relevant changes supporting the recovery process in stroke. Whilst changes in the lesioned hemisphere persisted over the period of recovery in all patients, contralesional intracortical hyperexcitability persisted in patients with cortical strokes and those with more severe baseline functional impairment, suggesting that ongoing contralesional network recruitment may be necessary for those patients who have significant disruptions to the integrity of ipsilesional motor pathways. The study has demonstrated that evolution of cortical excitability, particularly over the contralesional hemisphere, may vary between patients with differing baseline stroke and clinical characteristics, and thereby has important implications towards the development of protocols for neuromodulatory brain stimulation in stroke recovery.