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.