Optogenetic Stimulation of Inferotemporal Cortex is Perceived Earlier than Stimulation

Local stimulation in high-level cortical visual areas perturbs the contents of visual perception. We have previously demonstrated that visual events evoked by optogenetic stimulation in IT cortex can be reconstructed using a method dubbed “perceptography”. While perceptography informs about the contents of stimulation-evoked perceptual events, we do not know when they are perceived relative to external physical events. In this study, we use high throughput behavioral optogenetics coupled with visual interference to measure when stimulation-evoked perceptual events are perceived relative to concurrent sensory input. An adult macaque monkey was trained to behaviorally detect and report a brief optogenetic excitatory impulse delivered to its central IT cortex. The animal started each 1.6s trial by fixating on a randomly chosen computer-generated image (8 deg.). A ~1x1mm area of the IT cortex was optogenetically stimulated in half of the trials at random for 60ms halfway through the image presentation using an implanted LED array. We hypothesize that interrupting the image presentation at the proper time can mask the stimulation-evoked perceptual event. This was accomplished by presenting high-contrast visual noise (12 deg.) at one of 11 different time points during image presentation. After each trial, the animal reported whether it was stimulated by looking at one of two presented targets, with liquid reward for correct reports. We find that the monkey’s performance varies with the onset time of the visual noise. Presentation of visual noise 200ms prior to stimulation elicited a significantly larger miss rate compared to baseline. This is reflected by a significant decrease in the monkey’s d’ for the same noise onset time against baseline. Furthermore, we find that perceptography with image perturbations presented 200ms prior to stimulation induces a higher false alarm rate compared to image perturbation presented simultaneously to stimulation.