Stability of steady-state visual evoked potential contrast response functions
A repeated measure of neural activity that is stable over time when unperturbed is needed to be able to meaningfully measure neuroplastic changes in the brain. With sensory-evoked potentials in particular, repeated presentation of stimuli can generate neuroplasticity by itself under certain conditions. We assessed the repeated-measure within-day and across-day stability of the steady-state visual-evoked potential (ssVEP), a high signal-to-noise electrophysiological readout of neural activity in human visual cortex, in preparation for studies of visual cortical neuroplasticity. Steady-state VEP contrast-sweep responses were measured daily for 4 days (four 20-trial blocks per day, 22 participants). Response amplitudes were stable in individual participants, with measured across-block and across-day coefficients of variation (CV= SD / Mean) of 12{+/-}1% and 19{+/-}2%, respectively. No consistent changes in response amplitude were observed either across blocks or across days. We conclude that contrast-sweep steady-state VEPs provide a stable human neurophysiological measure well-suited for repeated-measures studies.