Table 1. Differences between D-wave and muscle motor-evoked potentials (MEPs)

	D-wave	Muscle MEPs
Stimulation	Single-pulse transcranial electrical stimulation	Multipulse transcranial electrical stimulation
Recording	Near-field potentials of spinal cord using epidural or subdural electrodes	Electromyographic activity of muscles using surface or needle electrodes
Averaging	May not average or may average a small number of responses up to 20 stimuli	Should not average
Mechanism	Travelling neuronal activation without any synapse between the stimulated cortical pyramidal neurons and D-wave recording site	Muscle activation after neuromuscular junction and multi-synaptic transmission at the anterior horn cell
Relationship between neuronal injury and the signal change	Linear	Non-linear
Variability	Stable, low variability	Unstable, high variability