Corticospinal volleys evoked by transcranial electrical and magnetic stimulation

Abstract

Monitoring corticospinal function during surgery is now feasible and a number of different techniques have been implemented by different authorities, as discussed below. Based on recordings of somatosensory volleys using recording electrodes inserted into the epidural space, as pioneered by Jones and colleagues (1982, 1983), and the first report of corticospinal volleys recorded using similar electrodes (Boyd et al., 1986), our unit has developed a recording system that allows the simultaneous recording of descending corticospinal volleys and ascending somatosensory volleys from the spinal cord (Fig. 1), and has used it extensively, primarily during scoliosis surgery (Hicks et al., 1991; Burke et al., 1992b; Stephen et al., 1996). This chapter addresses the nature of the corticospinal volleys set up by electrical and magnetic stimulation of the human motor cortex through the scalp, as recorded using this technique. The data are relevant not only for those who monitor spinal cord function during surgery but also for those who use transcranial stimulation of the motor cortex as a diagnostic or research tool.