Silent period evoked by transcranial magnetic stimulation in unilateral thalamic infarcts

We studied 9 patients with isolated, unilateral thalamic infarcts of different location and size imaged by MRI and (in one case) by CCT. The cortical silent period (c-SP) of thenar muscles evoked by transcranial magnetic stimulation was evaluated on both sides with low (c-SP1) and high (c-SP2) stimulus intensity. Additionally, the motor-evoked thenar potentials by transcranial magnetic stimulation (MEP) and the central motor conduction time (CMT), the silent period of thenar muscles evoked by electrical median nerve stimulation (p-SP), electrically evoked short- (HR) and long-latency reflexes (LLR) of the thenar and somatosensory evoked potentials of the median nerve were investigated bilaterally. The c-SP1 was prolonged contralateral to the thalamic infarcts in 7 patients and c-SP2 in all 9 patients. Prolongation of c-SP did not correlate with location and size of the infarct, clinical symptoms or with the other parameters, which are based on pyramidal motor system (MEP, CMT), thalamocortical circuits (SEP, LLR), or spinal excitability level (p-SP, HR). These results suggest the central pathways of the c-SP to be independent from those of the remaining parameters and indicate the c-SP as a sensitive parameter reflecting thalamocortical modulation of cortical inhibition.