Central motor reorganisation following stroke and motor learning studied in man

Central motor reorganisation has been studied (i) in patients after cerebral stroke (ii) during normal ageing and (iii) in healthy subjects after learning a new motor skill. Cutaneomuscular reflex responses (CMRs) were recorded to investigate changes in spinal and transcortical reflex pathways, and cross-correlation analysis of multi-unit EMG signals was used to investigate changes in shared common synaptic drive to motoneurone pools of synergistic muscle pairs. In adult stroke patients, studied over time, those with poor recovery usually showed spinal latency E1 CMR responses on the stroke side which were 2-9 times larger than those on the non-stroke side. This was observed as soon as the patient could produce sufficient voluntary EMG to grip a dowel with the stroke hand, and did not change over 2 years. Patients with good recovery showed I1 and E2 cortical responses on the stroke side as soon as index finger abduction could be performed. A lack of cortical I1 and E2 responses with E1 spinal responses in the stroke hand more than twice the size of those on the nonstroke hand may predict poor functional outcome at 2 years. Patients with poor recovery also showed significantly less (or absent) synchrony between motor units of synergistic muscle pairs on the stroke side compared to the non-stroke side. Patients with good recovery showed similar or significantly more synchrony on the stroke side. In all healthy adults, the size of the E1, I1 and E2 CMR components were not significantly different when comparing the right and left hands. During grip and index finger abduction, E1 responses were significantly smaller in older adults (range 58-85 years) compared to younger adults (range 19-30 years) suggesting that changes in spinal reflex pathways may accompany normal ageing. I1 and E2 responses were not significantly different between the 2 groups. Older adults showed significantly longer duration central correlogram peaks between motor units of synergistic muscle pairs in the hand compared to young adults. Learning a novel motor skill using 1DI and ADM (non-dominant hand) was accompanied by a significant increase in the size of I1 and E2 cortical responses in both muscles. The size of E1 spinal response was significantly increased in ADM but significantly decreased in 1DI. This suggests that motor learning produced changes in both cortical and spinal pathways. There was no significant change in synchrony between motor units of synergistic muscle pairs involved in the performance of the novel task after training. In this thesis, changes suggesting motor reorganisation of the nervous system in 3 groups of subjects have been demonstrated. Of clinical relevance, exaggerated spinal E1 responses in the stroke hand may predict a poor functional outcome in stroke patients at 2 years