Probing prefrontal influences on the emergence of visual category representations

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To make sense of the world, our visual brain groups a vast amount of possible input patterns into a relatively small number of meaningful categories, such as faces or scenes. Cortical representations of these categories have long been assumed to emerge solely from feedforward processing. However, it has become increasingly clear that category representations in visual cortex are shaped by top-down connections from other brain areas, including the prefrontal cortex (PFC). The influence of PFC on visual processing raises the question to which extent top-down control from PFC is necessary for category representations to emerge. To answer this question, this project will study visual category representations when top-down control from PFC is impaired. Specifically, repetitive transcranial magnetic stimulation (TMS) will be used to disrupt PFC activity in healthy participants for up to 30 minutes. During this time period, we will probe visual category representations in a multi-modal approach. Analyzing fMRI and EEG recordings, we will precisely establish where and when brain representations of different visual categories emerge under normal processing and under impaired top-down control from the PFC. Comparing these recordings to computational feedforward models, we will quantify the extent to which prefrontal control overrides visual bottom-up processing. Finally, in behavioral categorization experiments, we will use a “dual-site” TMS design to simultaneously disrupt visual cortex and PFC. These experiments will causally demonstrate how feedforward processing converges with feedback from PFC to forge the category representations that guide our behavior. Our project will provide a comprehensive causal account of how PFC impacts visual category processing at the neuronal, computational, and behavioral level. Advances made in this project have the potential to provide us with better models of cortical communication and inspire new research into the consequences of impairments to this communication.