Figure 5. Descending volleys and EMG responses evoked by a threshold magnetic stimulus alone, a vertex anodal stimulus alone and both stimuli together.

Descending volleys (left) and EMG responses (right) evoked by a threshold magnetic stimulus alone (top traces) and a vertex anodal stimulus alone (second traces). The third trace is the electronic sum of the first two traces, whilst the fourth and bottom traces show the actual result of giving both stimuli together at an interval of 100 μs (fourth traces) and 500 μs (bottom traces). Stimulus intensity was just over AMT for both types of stimulation. There is little recognisable descending activity when magnetic or electrical stimuli are delivered alone, whereas there is a clear descending wave when both stimuli are delivered together at both interstimulus intervals (ISIs) studied. Note the corresponding increase in amplitude of the EMG response recorded simultaneously in the tibialis anterior muscle.