Collaborative Research: The Cognitive Neuroscience of Category Learning

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Cognitive Neuroscience of Category LearningAbstractWith National Science Foundation support, Drs. Gluck and Poldrack and colleagues will conduct a three-year investigation to test two hypotheses about the roles of the basal ganglia and medial temporal lobe, and their interaction, in human category learning. They will test these hypotheses using a combination of functional magnetic resonance imaging (fMRI) and studies of patients with damage to either the basal ganglia (due to Parkinson's disease) or to the medial temporal lobe (due to anoxia or other causes). The first hypothesis to be tested is that the basal ganglia are particularly important for learning based on trial-by-trial feedback, whereas the medial temporal lobe is more important for observational learning in the absence of feedback. The second hypothesis is that the engagement of these two regions during category learning is modulated by the structure of the category that is being learned. For example, some categories are largely determined by single features; for example, most animals with a beak are classified as birds. Other kinds of categories require integration of information across multiple features. We will test the hypothesis that the medial temporal lobe is crucial for learning categories based on combinations of features, whereas the basal ganglia are important for learning categories based on single features.The topic studied in this project is categorization, oneof the most important acts of human cognition. Categorization is the recognition that various individual objects can be classified into larger groups that resemble each other in some way. Research in cognitive psychology has provided a set of sophisticated models for how humans learn new categories. However, little is currently known about how these operations are achieved in the brain. Most of our current knowledge comes from studies of patients with brain disorders. In particular, patients with Parkinson's and Huntington's diseases have trouble learning some kinds of new categories, though they are able to learn other kinds of categories. These diseases affect a set of deep brain structures known as the basal ganglia, and their impairment on some category learning tasks suggests that the basal ganglia may be critical for category learning. However, the exact role of the basal ganglia is unknown. Whereas patients with Parkinson's and Huntington's diseases are severely impaired at learning some new categories, patients with amnesia following damage to the medial temporal lobe (including the hippocampus) are only subtly impaired at category learning. Initial neuroimaging studies have shown that this region is deactivated when normal individuals are learning new categories, suggesting that it is not involved. Furthermore, imaging studies have shown that that activity in the medial temporal lobe and basal ganglia during category learning is negatively related: Individuals with more activity in one region tend to have less activity in the other. These findings suggest that these two regions may interact during learning, but the nature of this interaction is unclear at present.These studies have important implications, both for the basic understanding of category learning and for the understanding of the brain systems involved in such common disorders as Parkinson's and Alzheimer's diseases. Most importantly, the results of these studies will provide stronger constraints on theories of human category learning that are currently possible using behavioral measures alone.