Cracco J B, Amassian V E, Cracco R Q, Maccabee P J
Department of Neurology, State University of New York, Brooklyn 11203.
J Clin Neurophysiol. 1990 Jan;7(1):3-15. doi: 10.1097/00004691-199001000-00003.
The results of the following selected studies using magnetic coil (MC) stimulation are presented: (1) evidence for focality of MC stimulation, (2) MC stimulation of frontal areas related to speech, (3) transcallosal responses evoked by MC stimulation, and (4) suppression of visual perception with MC stimulation over occipital cortex. The authors served as subjects, and in most studies a standard Cadwell stimulator and round MC were used. Using a more vertical, rather than tangential, MC orientation and threshold stimulation, nearly isolated movements of individual digits were elicited implying focal cortical excitation. MC stimulation of frontal areas of either hemisphere elicited electromyography in contralateral laryngeal muscles. The shortest latency responses that were often accompanied by arm movement were thought to be elicited from intermediate areas of precentral gyrus and longer latency responses, from near Broca's area, extreme lateral precentral gyrus, and the supplementary motor area. MC stimulation over the occipital cortex resulted in suppression of visual perception of letters briefly flashed on a screen. The topography of suppression implicated the geniculocalcarine system as the site of MC effect. Focal MC stimulation of posterior frontal cerebral cortex elicited a transcallosal response from contralateral homologous cortex with a latency similar to that obtained with focal anodic stimulation but with considerably less excitation of cranial muscles.
