Alvin Dinh¹, Reza Azadi¹, Arash Afraz¹; ¹NIMH

We have previously demonstrated that the detectability of stimulation in the inferior temporal (IT) cortex of monkeys varies with the visual stimuli presented. Particularly, detectability is lowest when no image is shown to the animals. This suggests that the perturbability of neurons in the IT cortex depends on the cortical activity state, which is influenced by visual inputs. Consequently, identical cortical stimulation can evoke different levels of neuronal activation depending on the visual stimulus. To investigate this interaction, we employed optogenetic stimulation using the excitatory vector pAAV-CaMKIIa-C1V1(t/t)-TS-EYFP, targeting excitatory neurons. Monkeys were trained to maintain central fixation, while a series of images were presented for 1 second each, with 200 ms intervals between images. During half of the image presentations, randomly selected, a square light pulse was delivered to the transduced tissue 400 ms after image onset, lasting for 200 ms. Our results indicate that in conditions where no image was displayed, neural activity during cortical stimulation was significantly lower. This finding aligns with the animals' reduced performance in detecting cortical stimulation in the absence of visual stimuli, suggesting that the perturbability of the stimulated site is modulated by visual input.

Acknowledgements: NIMH Intramural Research Training Award (IRTA) Fellowship Program; NIMH Grant ZIAMH002958