Neural mechanisms of adaptation in inferior temporal cortex: an optogenetic and pharmacological analysis.

Neurons in sensory brain areas change their responses to a stimulus after being exposed recently to that stimulus. This “adaptation” is a kind of short-term plasticity of the brain. Adaptation effects vary amongst brain regions and range from a suppression of the response to a repeated stimulus (“repetition suppression”) to an enhancement of the response to repeated stimuli. Repetition suppression is prominent in the inferior temporal (IT) cortex, which analyzes object properties for recognition. The phenomenon of repetition suppression is employed in basic and clinical human functional imaging studies. Also, adaptation in human temporal cortex is impaired in brain disorders. Despite the theoretical and clinical importance of adaptation in IT, its neural mechanisms underlying are still poorly understood. Primate IT cortex has no clear homology in rodents, and thus an understanding of adaptation mechanisms in IT requires work in primates, in particular in macaques. In this project, we will use (1) optical stimulation of IT neurons using optogenetic tools (an innovation in neurophysiology) and (2) injection of neurotransmitter receptor antagonists. These will be combined with microelectrode recordings to gain a mechanistic understanding of adaptation in IT. We will consider adaptation effects occurring within a cell and originating within the neuronal network. These studies will elucidate the mechanisms of adaptation within IT, bypassing processing at earlier cortical levels.