Changes in intracortical excitability in both hemispheres in patients affected by stroke during the motor recovery

The aim of the study was to investigate the motor excitability in patients affected by unilateral ischemic stroke during the acute period and the recovery, using paired pulse magnetic stimulation. We studied 10 patients (4 females, 6 males), ranging in age from 56 to 79 years. The stroke was subcortical in four patients and cortical in six patients. We studied the paired pulses magnetic stimulation using first a subthreshold-conditioning stimulus preceding the suprathreshold magnetic stimulus at different interstimulus intervals. In a healthy control group (10 subjects), the conditioning stimulus produced a suppression of test motor-evoked potential (MEP) (intracortical inhibition) at short ISI (1-4 ms) while produced facilitation (intracortical facilitation) at long ISI (7-15 ms). Furthermore, other parameters of transcranial magnetic stimulation (TMS) were studied: motor threshold, latency and amplitude of MEP and central conduction time (CCT). The recordings were perfomed within 10 days from the acute event (T1) and after 1 month (T2) from the stroke. During the acute period the intracortical inhibition was significantly reduced in the affected (in those subjects in whom the MEP was present) and in the unaffected hemisphere. Significant asymmetries in motor threshold, MEP latency, MEP amplitude and CCT were noted between the two hemispheres. In five patients with good recovery the intracortical inhibition was abnormal during the early period of recovery (T1) in both hemispheres but showed a significant reduction at the third recording (T2) which was associated with an important clinical improvement. In five patients with incomplete recovery, the intracortical inhibition was persistently abnormal in the affected and unaffected hemisphere. Motor threshold was significantly lower in the unaffected hemisphere than in control group. Mild changes in other TMS parameters were observed in both groups. The data suggest changes in motor excitability in both hemispheres in patients affected by stroke. Changes in intracortical excitability in the affected hemisphere seem to be related to the amount of motor recovery, suggesting a different hypothesis related to the time course and the kind of the recovery.