Using Stimulus-Response Curves to Determine Corticospinal Excitability

The excitability of the corticospinal tract can be quantified through the application of single-pulse transcranial magnetic stimulation (TMS) over the primary motor cortex (M1) and simultaneously recording the neurophysiological response at the target muscle through electromyography (EMG). In this chapter, we introduce the technique for constructing stimulusresponse (S-R) curves and the common methods employed to characterise the input-output properties of the corticospinal tract. We then describe the neurophysiological correlates of S-R curves and the physiological factors that can influence the TMS responses during the construction of an S-R curve, including age.