REORGANIZATION OF MOTOR OUTPUT IN THE NON-AFFECTED HEMISPHERE AFTER STROKE

Motor evoked responses to focal transcranial magnetic stimulation were investigated over the unaffected hemisphere in 15 patients with hemip aresis after ischaemic stroke and compared with data from normal contr ol subjects. Whereas responses to muscles ipsilateral to the stimulate d hemisphere could only be elicited at maximal intensities in two out of 12 normal control subjects, such ipsilateral responses were recorde d after stimulation of the unaffected hemisphere in patients with poor recovery after stroke at significantly lower thresholds, but not in p atients with good recovery These responses occurred with a somewhat lo nger (on average 6 ms) latency than the typical contralateral response . The duration of the silent period ipsilateral to stimulation of the unaffected hemisphere was longer than in control subjects. Also the co ntralateral threshold for the unaffected hemisphere was elevated in co mparison with the control group. In one patient who developed mirror m ovements after stroke, the ipsilateral threshold was exceptionally low and the latency of the ipsilateral response identical to that seen co ntralaterally It is concluded that the motor outputs in the unaffected hemisphere are significantly changed after stroke, including the unma sking of ipsilateral corticospinal projections. However these pathways seem to be of little significance for recovery, as the existence of t hese responses was not correlated with clinical improvement. The unaff ected hemisphere after stroke shows plastic changes in motor output or ganization after a contralateral lesion.