Figure 2. Mean amplitude of the epidural volleys evoked by magnetic stimulation using increasingly strong stimulus intensities and with different degrees of voluntary contraction.

Histograms showing the mean amplitude of the different epidural volleys recorded in the three patients during stimulation at different intensities and with different levels of background contraction. The amplitude of the volleys is larger during contraction, and the threshold for evoking the later I-waves and the D-wave is higher than that for the early waves. The average standard error limit on these bars was 11 μV.