Wednesday, April 2, 2025
4/2/2025
How do cortical hierarchies mediate visual categorization - Project summary One of the primary goals of the primate brain is to learn about structure in the world, and to shape neural representations such that they encode this structure in an efficient, generalizable format. An important behavior that relies upon the formation of these abstract neural representations is categorization, the process by which objects that may differ in their basic sensory features are assigned to the same behavioral output. Decades of research on the neural basis of categorization has contributed substantially to our understanding of the mechanisms underlying the representation of learned categories, and has led to the identification of a widely-distributed network of brain areas that may be involved, such as the lateral intraparietal region (LIP), prefrontal cortex (PFC), and superior colliculus (SC). However, prior work has almost exclusively relied on tasks that involve teaching non-human primates (NHPs) to assign stimuli to categories using a single visual feature, such as motion direction or color. Natural categorization, in contrast, often requires the integration of multiple features in order to determine to which category an object belongs (multi-feature integration categorization). Categorization and category-learning are disrupted in a number of neurological disorders, such as Alzheimer’s Disease, Parkinson’s, and ADHD, and multi-feature integration categorization seems to show a different pattern of deficits in these disorders than simpler category structures. This suggests that the circuit mechanisms mediating categorization or category learning may differ, depending on task demands. However, little is currently known about mechanisms of stimulus categorization when assignment to the correct category first requires the integration of disparate sensory features. A greater understanding of the neural mechanisms that support feature-integration for categorization will enhance our ability to provide targeted treatment for disorders that disrupt the categorization system. This work will involve conducting large-scale simultaneous electrophysiological recordings in two regions that have been implicated in mediating categorization; LIP and PFC. In Aim 1, neural activity in areas LIP and PFC will be recorded while NHPs switch between performing a multi-feature integration categorization task in which the direction of motion and the color of a moving-dot stimulus must be combined to determine the category, and a motion-direction categorization task in which only the direction of motion is relevant. In Aim 2, paired recording-inactivation experiments will be performed in which LIP (or PFC) will be reversibly inactivated while recording in PFC (or LIP). The results from this study will reveal what computations are necessary to perform categorization tasks of complex structure in which multiple sensory features must be combined or integrated, and how these demands shape the neural mechanism the brain uses to perform these tasks. Further, this work will elucidate the circuit mechanisms underlying categorization behavior through the use of simultaneous multi-area recordings and paired inactivation-recording experiments.
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