Stability of steady-state visual evoked potential contrast response functions

Repetitive sensory stimulation has been shown to induce neuroplasticity in sensory cortical circuits, at least under certain conditions. We measured the plasticity-inducing effect of repetitive contrast-reversal- sweep steady- state visual-evoked potential (ssVEP) stimuli, hoping to employ the ssVEP's high signal- to- noise electrophysiological readout in the study of human visual cortical neuroplasticity. Steady- state VEP contrast- sweep responses were measured daily for 4 days (four 20- trial blocks per day, 20 participants). No significant neuroplastic changes in response amplitude were observed either across blocks or across days. Furthermore, response amplitudes were stable within-participant, with measured across- block and across- day coefficients of variation (CV = SD/mean) of 15-20 +/- 2% and 22- 25 +/- 2%, respectively. Steady- state VEP response phase was also highly stable, suggesting that temporal processing delays in the visual system vary by at most 2- 3 ms across blocks and days. While we fail to replicate visual stimulation-dependent cortical plasticity, we show that contrast- sweep steady-state VEPs provide a stable human neurophysiological measure well suited for repeated-measures longitudinal studies.