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The Journal of Neuroscience, June 24, 2009, 29(25):8280-8287; doi:10.1523/JNEUROSCI.1176-09.2009

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Behavioral/Systems/Cognitive
Evidence of Action Sequence Chunking in Goal-Directed Instrumental Conditioning and Its Dependence on the Dorsomedial Prefrontal Cortex

Sean B. Ostlund,¹ Neil E. Winterbauer,³ and Bernard W. Balleine^2,4

¹Semel Institute for Neuroscience and Human Behavior and ²Department of Psychology and Brain Research Institute, University of California, Los Angeles, Los Angeles, California 90095, ³Department of Psychology, University of Vermont, Burlington, Vermont 05405, and ⁴Brain & Mind Research Institute, University of Sydney, Sydney, New South Wales 2006, Australia

Correspondence should be addressed to Sean B. Ostlund, Department of Psychology and Brain Research Institute, Franz Hall, Box 951563, University of California, Los Angeles, Los Angeles, CA 90095-1563. Email: sostlund{at}ucla.edu

The current study investigated the contribution of the dorsomedial prefrontal cortex (dmPFC) to instrumental action selection. We found that cell body lesions of the dmPFC, centered on the medial agranular area, spared rats' ability to choose between actions based on either the value or the discriminative stimulus properties of an outcome. We next examined the effects of these lesions on action sequence learning using a concurrent bidirectional heterogeneous chain task in which the identity of the reward delivered was determined by the order in which the two lever press actions were performed. Although both lesioned rats and sham controls learned to perform the task, we found that they relied on different behavioral strategies to do so. In subsequent tests, rats in the sham group were able to withhold their performance of a sequence when either its associated outcome was devalued or the contingency between that sequence and its outcome was degraded by delivering the outcome noncontingently. Interestingly, lesioned rats failed to reorganize their performance at the action sequence level and, rather, were found to withhold their performance of the terminal response in the sequence that had earned the devalued outcome relative to the more distal response, suggesting that they represented the elements of the sequence as distinct behavioral units. These findings demonstrate that rats can use sequence-level representations, or action chunks, to organize their behavior in a goal-directed manner and indicate that the dmPFC plays a critical role in this process.

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Received March 10, 2009; revised April 29, 2009; accepted May 8, 2009.

Correspondence should be addressed to Sean B. Ostlund, Department of Psychology and Brain Research Institute, Franz Hall, Box 951563, University of California, Los Angeles, Los Angeles, CA 90095-1563. Email: sostlund{at}ucla.edu

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