Patricia Limon¹, Anthony Norcia¹, Ryan Ash¹; ¹Stanford University

Passively viewing a 2 Hz contrast-reversing stimulus potentiates visual evoked responses in humans and rodents, enabling quantification of experience-dependent visual cortical neuroplasticity coined stimulus-specific response potentiation (SSRP). SSRP demonstrates input-specificity, retinotopic-specificity, and accumulates across days. While attention is known to modulate learning and plasticity, its impact on SSRP remains under-investigated. We hypothesized that directing spatial attention toward an SSRP-induction stimulus would enhance response potentiation within its retinotopic extent, while diverting attention would diminish it. Stimuli consisted of 2 semicircular hemifield checkerboards (10° eccentricity), each frequency-tagged to measure EEG steady-state visual-evoked potentials, using a 128-channel system. Participants (n=26) observed contrast-sweeps of the checkerboards before and after SSRP-induction, with sign-reversal rates of 6 Hz and 7.5 Hz (non-plasticity inducing), maintaining fixation via a letter-detection task. During SSRP-induction, the left checkerboard (100% contrast, 2 Hz reversal) served as the potentiation stimulus, while the right checkerboard (2% contrast, 3 Hz reversal) was the non-potentiated control. Via a contrast change detection task, participants directed peripheral attention to the potentiating stimulus (Potentiation-Attention Congruent) or the control (Potentiation-Attention Incongruent) on separate sessions. We observed a modest increase in response amplitude following SSRP that did not initially appear to depend on the attention condition. Interestingly, we observed that potentiation occurred exclusively on the second experiment day, suggesting that the SSRP effect accumulates across days. The enhancement was more pronounced at higher contrasts. Contrary to expectation, SSRP was not retinotopically specific, occurring in both hemifields. Second-day SSRP response enhancement occurred in both attention conditions; however, a significant three-way interaction (P=0.0005, VEP response x session day x attentional deployment) indicated that the sequence of attentional conditions (Day 1 congruent, Day 2 incongruent vs. Day 1 incongruent, Day 2 congruent) impacts SSRP development. Our findings demonstrate stimulus-induced neural plasticity in the visual cortex that dynamically evolves across sessions.

Acknowledgements: National Eye Institute