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Proc Natl Acad Sci U S A. 2010 Aug 17;107(33):14839-44. doi: 10.1073/pnas.1009433107. Epub 2010 Aug 2.

Successive-signal biasing for a learned sound sequence.

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School of Life Sciences, Institute of Cognitive Neuroscience, East China Normal University, Shanghai 200062, China.


Adult rats were trained to detect the occurrence of a two-element sound sequence in a background of nine other nontarget sound pairs. Training resulted in a modest, enduring, static expansion of the cortical areas of representation of both target stimulus sounds. More importantly, once the initial stimulus A in the target A-B sequence was presented, the cortical "map" changed dynamically, specifically to exaggerate further the representation of the "anticipated" stimulus B. If B occurred, it was represented over a larger cortical area by more strongly excited, more coordinated, and more selectively responding neurons. This biasing peaked at the expected time of B onset with respect to A onset. No dynamic biasing of responses was recorded for any sound presented in a nontarget pair. Responses to nontarget frequencies flanking the representation of B were reduced in area and in response strength only after the presentation of A at the expected time of B onset. This study shows that cortical areas are not representationally static but, to the contrary, can be biased moment by moment in time as a function of behavioral context.

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