Phelix Rodriguez¹, Bing Li¹, Mark AG Eldridge^1,2, Walter Lerchner¹, Barry J Richmond¹; ¹National Institute of Mental Health, ²Newcastle University

Image recognition depends on the ventral visual stream. Inferior temporal cortex (ITC) is a brain region thought to be the last element of the ventral visual stream. Previous studies have shown that neurons in higher level visual areas, including area TE, a subregion of ITC, exhibit less activity when presented with stimuli that subjects have seen previously, an effect known as ‘repetition suppression’. We have demonstrated that the bilateral lesion of area TE causes deficits in object recognition. We examined the role of area TE in image recognition using an inhibitory chemogenetic agent. Two rhesus monkeys received bilateral injections of virus expressing inhibitory DREADDs (designer receptors exclusively activated by designer drugs) to area TE. Subjects were trained to complete a ‘serial recognition’ task by incorporating progressively longer intervals (more intervening trials) between first and second presentations of a novel stimulus. Subjects were tested on two versions of the serial recognition task with all interval sizes (0-128 trials between first and second presentation), one with continuously presented stimuli and the other with briefly presented stimuli, after receiving a systemic injection of either saline or DREADD-activating ligand, deschloroclozapine (DCZ). Early results show a reduction in overall task performance and a higher rate of objects reported as familiar using briefly-presented stimuli but not on the task using continuously-presented stimuli. Thus, area TE is needed to identify a briefly-presented stimulus as unfamiliar. The inhibitory effects of DREADDs on TE activity may mimic the repetition suppression, which leads to increased reporting of familiarity.

Acknowledgements: Intramural Research Program; National Institute of Mental Health; National Institutes of Health; Department of Health and Human Services (annual report number ZIAMH002032)