Post-stroke reorganization of brain motor output to the hand: a 2–4 month follow-up with focal magnetic transcranial stimulation

Abstract

Focal transcranial magnetic stimulation (TCS) was employed for the representation of the motor cortex in a population of 18 patients to investigate the functional properties of hand motor areas 2–4 months after a monohemispheric stroke. Eleven sites were stimulated to elicit motor evoked potentials (MEPs) in abductor digiti minimi muscle after TCS of affected (AH) and unaffected (UH) hemispheres; recording sessions were performed at the beginning (T1) and after 8–10 weeks (T2) of neurorehabilitation. Barthel index and Canadian neurological scale scores were evaluated. A group of 20 healthy control subjects was enrolled. In stroke patients the AH was less excitable than normal, combined with a decrease in motor cortical output area (P<0.05) in T1. In T2, there was an enlargement of the hand motor area on the AH combined with an improvement of clinical scores (P<0.001). In T1 and T2, the amplitude of MEPs in the AH was reduced (P<0.001) with a prolongation of central conduction time (P<0.001) and with a tendency towards improvement in T2; the amplitude of contracted MEPs was larger than normal in the UH in T1. Both in T1 and T2, anomalous `hot spot' (most excitable) scalp sites, never seen in normals, were often encountered (T2>T1) on the AH and UH. Interhemispheric differences for topography and latency of MEPs were remarkably affected. Our data are consistent with a rearrangement of the brain motor cortical output between 2 and 4 months following stroke. The amelioration of the neurophysiological parameters was correlated with clinical improvement in disability and neurological scores. This study confirms the existence in adults of brain `plasticity' still operating between 2 and 4 months from an acute vascular monohemispheric insult.