Figure 2. Relationship between the amplitude of the costal diaphragm MEP and coil position relative to the vertex.

Individual and mean responses are represented by dashed and continuous lines, respectively. All stimulations were performed at 100% of stimulator output. Values are expressed as a percentage of the response elicited at the vertex. Each square corresponds to the mean of an individual subject. Each triangle corresponds to the mean (+ s.e.m.) of eight subjects. MEP amplitude varied significantly with change in coil position (P < 0.0001). The response to stimulation was characterized by two peaks representing the primary motor cortex (vertex) and supplementary motor area (vertex + 3 cm).