title: Anodal and cathodal stimulation of the upper-limb area of the human motor cortex.
abstract: In 18 neurologically normal subjects the corticofugal volleys evoked by anodal and cathodal electrical stimulation of the motor cortex were recorded using epidural electrodes at the high-thoracic and low-thoracic regions of the spinal cord during surgery for scoliosis. At and just above threshold, anodal and cathodal stimulation of the upper-limb area and motor cortex produced a D wave that propagated to the low-thoracic region. The stimulus intensity required to produce D waves was significantly lower with anodal stimulation. I waves were recorded at higher stimulus intensities than the D wave but not more readily with cathodal stimulation. There was no significant difference in the extent to which stimulus intensity had to be increased above D-wave threshold to produce I waves with the two stimulus polarities, and the number of I waves was the same when the stimulus was increased by the same amount above D-wave threshold. After withdrawal of isoflurane, I waves could not be recorded when the stimulus intensity was below D-wave threshold with either stimulus polarity. Anodal stimulation over the upper-limb area remained more effective than cathodal stimulation in producing both D and I waves. These results indicate that, at threshold, regardless of anaesthesia, anodal and cathodal stimuli access upper-limb corticospinal neurons directly at a similar site, the anodal stimuli being more effective. In addition, the results suggest that some corticospinal neurons in the upper-limb area of motor cortex have projections to lumbar segments.
authors.affiliation: Department of Clinical Neurophysiology, Prince Henry Hospital, Little Bay, NSW, Australia.
authors.forename: D
authors.initials: D
authors.lastname: Burke
authors.forename: R
authors.initials: R
authors.lastname: Hicks
authors.forename: J
authors.initials: J
authors.lastname: Stephen
mesh_terms: D000293:Adolescent; D000328:Adult; D000758:Anesthesia; D001132:Arm / Q000502:physiology*; D002648:Child; D004558:Electric Stimulation; D004566:Electrodes; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*; D011930:Reaction Time