iGluSnFR wide-field imaging responses to 2-72 Hz flicker

Human primary visual cortex (V1) responds more strongly, or resonates,
when exposed to ~10, ~15-20, ~40-50 Hz rhythmic flickering light.
Full-field flicker also evokes perception of hallucinatory geometric
patterns, which mathematical models explain as standing-wave formations
emerging from periodic forcing at resonant frequencies of the simulated
neural network. However, empirical evidence for such flicker-induced
standing waves in the visual cortex was missing. We recorded cortical
responses to flicker in awake mice using high spatial resolution widefield
imaging in combination with high temporal resolution glutamate-sensing
fluorescent reporter (iGluSnFR). The temporal frequency tuning curves in
the mouse V1 were similar to those observed in humans, showing a banded
structure with multiple resonance peaks (8 Hz, 15 Hz, 33 Hz). Spatially,
all flicker frequencies evoked responses in V1 corresponding to
retinotopic stimulus location, but some evoked additional peaks. These
flicker-induced cortical patterns displayed standing wave characteristics
and matched linear wave equation solutions in an area restricted to the
visual cortex. Taken together, the interaction of periodic traveling waves
with cortical area boundaries leads to spatiotemporal activity patterns
that may affect perception.