Repetitive paired-pulse transcranial magnetic stimulation over the visual cortex selectively inhibits focal flash VEPs

Background The human visual system processes different aspects of visual information such as luminance and contrast via multiple channels. We previously used repetitive paired-pulse stimulation (rPPS) over the visual cortex to elicit a disinhibitory effect on the visual recovery function of paired pattern-reversal (PR) visual evoked potentials (VEPs). Objective We tested the hypothesis that different visual channels exhibit diverse response patterns after rPPS over the visual cortex. Thus, we examined how rPPS influenced each channel of the visual cortex. Methods We employed rPPS with a 1.5-ms interstimulus interval over the visual cortex at the stimulus intensity of the visual masking effect. Focal flash (FF) and PR-VEPs (check size, 15 min) were recorded to evaluate the response properties of visual channels in 10 healthy subjects. Visual stimuli were presented for the lower half-field that subtended 6 in radius. The amplitudes and latencies of each VEP were compared before and after rPPS for up to 30 min. Results Following rPPS, N1-P1 and P1-N2 amplitudes of FF-VEPs decreased linearly up to 30 min. In contrast, the amplitudes of PR-VEPs were not significantly changed. Latencies of FF- and PR-VEPs were also unchanged. Conclusions Modulation of FF-VEPs by rPPS suggests that rPPS selectively induced an inhibitory effect on the luminance channel. Therefore, rPPS may be a promising tool for exploring plastic changes in the visual cortex.