Visual masking with frontally applied pre-stimulus TMS and its subject-specific neural correlates.

The visibility of a visual target stimulus depends on the local state of the early visual cortex shortly before the stimulus itself is presented. This view is supported by the observation that occipitally applied pre-stimulus TMS can disrupt subsequent information processing leading to visual masking effects. According to another line of accumulating evidence, however, global pre-stimulus connectivity patterns could be as crucial as local cortical states. In line with the latter view we show that pre-stimulus masking occurs even if TMS is directed to the frontal cortex. Importantly, the individual extent of this effect is strongly correlated with the subject-specific peak latency of a late positive TMS-evoked potential. Our results thus suggest a third type of masking occurring neither through direct interaction with visual areas nor by a modal visual masking input. Our results also shed light on the inter-individual differences in TMS research in general.