TEMPORAL ASPECTS OF VISUAL AND THALAMIC OPTOGENETIC ACTIVATION OF PRIMARY VISUAL CORTEX

Optogenetic stimulation triggers an artificial activation in neural circuits that can differ dramatically from endogenous or sensory-driven activity in those same circuits. Our understanding of these differences and how they arise is at present incomplete. Here we investigate this issue by activating tree shrew primary visual (V1) cortical circuits using temporally modulated visual input (full field flicker at 5, 10, 15, 20, 30 and 40Hz at 50% duty cycle) and optogenetic activation of visual thalamic (VT) projections using AAV-hSyn-ChR2 optogenetic activation with the same temporal profile. We have preliminary data from laminar V1 recordings using high density probes, in visual, optogenetic and combined simultaneous visual+optogenetic stimulation conditions. We found that visual and VT-ChR2 stimulation produced highly distinct temporal activation profiles, such that neural activation peaks for visual flicker occurred at about 20Hz flicker frequency with an overall inverted U-shaped profile, whereas VT-ChR2 activation peaked at 5Hz and exhibited a monotonic decrease with increasing frequency. We discuss laminar aspects of evoked activation patterns and relate these neural circuit findings to perceptual ability of tree shrew in discriminating between temporally modulated visual stimuli. Our findings advance the understanding of the relation between natural and artificial stimulation of the visual pathway and may have important implications for a next generation of visual prostheses that rely on optogenetics.