Spatial Attention and Session Day Jointly Modulate Human Visual Cortical Plasticity

Visual-evoked potential plasticity (VEPP) is a noninvasive form of cortical neuroplasticity elicited by repeated presentation of high-contrast visual stimuli. In rodent models, stimulus-specific response potentiation (SSRP) effects accumulate across days; however, it remains unclear whether repeated exposure across days influences the magnitude or specificity of potentiation in humans. In addition, visual cortical plasticity may not be determined by experience alone: voluntary attentional deployment selects which inputs are prioritized, and may thereby determine how much a given amount of sensory experience alters cortical excitability. Here, we examined whether covert spatial attention and repeated exposure across days modulate VEPP strength using high-density electroencephalography (EEG) in neurotypical adults. An established VEP modulation paradigm was modified to use steady-state visual evoked potential (SSVEP) stimuli, which we refer to as steady-state visual response potentiation (SSVRP). Pre- and post-induction amplitudes were measured using frequency-tagged (6 and 7.5 Hz) bilateral hemifield contrast-sweep checkerboard steady-state visual evoked potentials (SSVEPs). A 10-min, high-contrast, 2 Hz sign-reversing induction stimulus was presented exclusively to the left hemifield, with the right serving as control. Across two experimental sessions, participants attended either toward or away from the potentiated hemifield during induction. Notably, attention enhanced SSVRP in the first session day but not the second session day, reflecting a significant interaction between attention and session day. Potentiation was significantly greater on the second session day, independent of attention condition. Of note, potentiation occurred in both hemifields despite the potentiating stimulus only being presented in the left hemifield. Our results tentatively suggest that spatial attention and experience jointly modulate human visual cortical plasticity.