Influence of peripheral nerve stimulation on human motor cortical excitability in patients with ventrolateral thalamic lesion
F. Hirashima and T. Yokota
Department of Neurology, Tokyo Medical and Dental University, Tokyo, Japan.
OBJECTIVE: To determine the peripheral afferent pathways that influence the
activities of the motor cortex by examining the effects of peripheral nerve
stimulation on motor cortical excitability. PATIENTS AND METHODS: We
examined 12 healthy volunteers and 4 patients with localized brain lesions
caused by cerebrovascular attack. Of the 4 patients, 1 patient had pontine
infarction, including medial lemniscus, and severe sensory deficit and 3
had small localized lesions in the lateral part of the thalamus and neither
sensory impairment nor abnormal N20 waves on somatosensory evoked potential
recordings. Central motor tract excitability was examined by measuring a
change in the motor evoked potential (MEP), using transcranial magnetic
stimulation of the motor cortex after peripheral nerve stimulation at the
wrist significantly increased MEP response in the controls at long
conditioning-test intervals of 28 to 60 milliseconds, as well as at short
intervals of 0 to 6 milliseconds. A late MEP potentiation was not observed
on the affected side in all patients. CONCLUSIONS: The loss of late MEP
potentiation in patients with pontine and thalamic lesions indicates that
this potentiation is caused by the alternation of the motor cortical
excitability. Furthermore, the results in the patients with thalamic
lesions suggest that the lateral nuclei of the thalamus, other than the
ventral posterolateral nucleus and probably including the ventrolateral
nucleus, have an important function in the processing of peripheral sensory
input for tuning motor cortical excitability.
