Stages of Motor Output Reorganization after Hemispheric Stroke Suggested by Longitudinal Studies of Cortical Physiology

TLDR

Reorganization of motor circuits in the cerebral cortex is thought to contribute to recovery after stroke, yet little is known about how these changes develop during the early post‑stroke period and influence recovery. The study used TMS to obtain bilateral measures in 10 patients from the early days to 6 months post‑stroke in order to examine correlations with hand‑function tests. The authors employed TMS to assess corticospinal tract integrity and intracortical excitability bilaterally in patients and healthy controls, collecting data from early days to 6 months post‑stroke. Day‑to‑day performance variation was unrelated to physiological measures in the first 3 weeks, yet corticospinal integrity correlated with hand function during that period—a relationship that weakened by 3 months—while intracortical excitability showed no acute correlation but did so strongly at 3 months, suggesting that early performance is limited by corticospinal damage and later improvement depends on reorganization of alternative cortical networks aided by intracortical disinhibition.

Abstract

Reorganization of motor circuits in the cerebral cortex is thought to contribute to recovery following stroke. These can be examined with transcranial magnetic stimulation (TMS) using measures of corticospinal tract integrity and intracortical excitability. However, little is known about how these changes develop during the important early period post-stroke and their influence on recovery. We used TMS to obtain multiple measures bilaterally in a group of 10 patients during the early days and weeks and up to 6 months post-stroke, in order to examine correlations with tests of hand function. Ten age-matched healthy subjects were also studied. After stroke, day-to-day variation in performance was unrelated to physiological measures in the first 3 weeks. Measures of corticospinal integrity averaged over the same period correlated well with hand function, but this relationship became weaker at 3 months. In contrast, most intracortical excitability measures did not correlate acutely but did so strongly at 3 months. Thus in the acute stage, patients' performance is limited by damage to corticospinal output. Improved performance at 3 months may depend on reorganization in alternative cortical networks to maximize the efficiency of remaining corticospinal pathways—intracortical disinhibition may aid recovery by promoting access to these networks.