A figure-8 coil was designed that was capable of generating currents over a relatively limited area. In this study, we used the figure-8 coil to localize human cerebral motor cortex by transcranial magnetic stimulation and assessed its value as a diagnostic tool for neurosurgical disease. The subjects were 10 normal volunteers and 12 neurosurgical patients. The points obtaining a response were plotted and the response area was delineated for each stimulus output. Rectangular coordinates were subsequently determined for the C3-Cz-C4 line with the stimulation sites set 1.0 cm apart. Then amplitude and latency maps were displayed by a computer wave map program. In normal volunteers, the posterior margin of the site where a threshold +5% stimulus obtained a response from the THE or ADM muscles almost coincided with the central sulcus. The optimal areas were relatively narrow on the amplitude and latency maps. In the patient with a left frontal convexity meningioma, the left threshold +5% area for the THE and ADM muscles showed marked anterolateral shift. No threshold map could be obtained on the affected side in patients with metastatic tumor and astrocytoma. Low perfusion areas caused by moyamoya disease and arteriovenous malformations produced narrowing of the optimal zone on the threshold map of the affected side. Hyperexcitability of the motor cortex was recognized in the arteriovenous malformation patients. Transcranial focal magnetic stimulation is a useful noninvasive diagnostic method for identification of the human cerebral motor cortex. It provides important information about changes in the localization and excitability of the motor cortex in neurosurgical patients and should be helpful for treatment planning.
Adult Brain Diseases