Human cerebral cortical responses to contralateral transcranial stimulation

Area of Science:

• Neuroscience
• Electrophysiology
• Brain Imaging

Background:

• Developing noninvasive electrophysiological measures of human cerebral cortex function is crucial.
• The transcallosal response (TCR), elicited by corticocortical input, is a potential candidate.
• Large shock artifacts complicate electrophysiological recordings during transcranial stimulation.

Purpose of the Study:

• To develop a noninvasive electrophysiological measure of human cerebral cortex functioning.
• To specifically utilize and refine the measurement of the transcallosal response (TCR).

Main Methods:

• Subjects were stimulated percutaneously with a focal anode and a medial cathode to minimize shock artifacts.
• Recording involved a focal scalp electrode over the left frontal cortex against distant reference electrodes.
• Transcranial stimulation parameters: 80-140 mA, 100-microsecond pulses.

Main Results:

• A brief diphasic deflection (2-4 ms latency) and a positive wave (9-14 ms latency) were elicited.
• The diphasic deflection was identified as electromyographic (EMG) in origin and artifactual.
• The positive wave's latency and rising phase were unaffected by reduced current or scalp circulation occlusion, suggesting a cortical origin.

Conclusions:

• The study successfully developed a method to elicit and record the transcallosal response (TCR) noninvasively.
• The identified positive wave is likely a valid electrophysiological measure of human cerebral cortex function.
• This technique offers a promising approach for studying corticocortical pathways.