Transcranial stimulation parameters to elicit motor evoked potentials

We studied effectiveness of single, paired, and repetitive transcranial electrical stimulation to activate motor cortex in patients during spine surgery.

In ten consented patients, the latency and amplitude of the muscle action potential from abductor pollicis brevis muscle after cortical stimulation was measured.

The number of responses evoked by double (pair) pulse stimulation was significantly higher than that evoked by single pulse (p = 0.0191). A similar finding was obtained between the repetitive and single pulse stimulation (p = 0.0001). The repetitive stimulation was more effective than the double pulse stimulation (p = 0.0253). An increase of interstimulus interval (ISI), between pulses, from 1-3 msec did not significantly alter latency (p > 0.05) or amplitude (p > 0.05) with the double pulse or repetitive stimulations. The latency or amplitude did not significantly change with varying number of electrical pulses from 3-9.

This study shows that the intraoperative repetitive transcranial stimulation is the most effective method to activate descending motor tracts under anesthesia.