Of Landmarks and Boundaries

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Science  11 Apr 2008:
Vol. 320, Issue 5873, pp. 156
DOI: 10.1126/science.320.5873.156b

The striatum and the hippocampus both have important functions in learning and memory. Despite decades of intensive investigation, there are still a number of incompletely resolved questions. What sort of information is processed in each structure? How do the hippocampus and striatum cooperate to influence behavior? What type of learning is performed by each? These issues are tackled in two related papers.

Using virtual reality and functional magnetic resonance imaging, Doeller et al. show that humans learn and remember the locations of objects relative to both local landmarks and environmental boundaries in parallel. The boundary-related system involves the right posterior hippocampus, whereas the landmark-related system involves the right dorsal striatum. When the hippocampal and striatal systems are in conflict because a landmark has been moved relative to the boundary, they do not compete directly to control behavior; instead, each system independently signals its solution to the task, with the ventromedial prefrontal cortex recruited for arbitration. Doeller and Burgess, using the same virtual reality object-location paradigm in behavioral experiments, show that striatal landmark-related processing of spatial learning obeys associative reinforcement learning, whereas hippocampal boundary-related processing does not. The latter performs purely incidental learning instead. Together, these studies provide evidence for the use of distinct learning rules in the hippocampus and striatum. — PRS

Proc. Natl. Acad. Sci. U.S.A. 105, 10.1073/pnas.0801489105; 10.1073/pnas.0711433105 (2008).

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