Medial prefrontal activity during delay period contributes to learning of a working memory task

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Science  24 Oct 2014:
Vol. 346, Issue 6208, pp. 458-463
DOI: 10.1126/science.1256573

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Cognitive processes require working memory (WM) that involves a brief period of memory retention known as the delay period. Elevated delay-period activity in the medial prefrontal cortex (mPFC) has been observed, but its functional role in WM tasks remains unclear. We optogenetically suppressed or enhanced activity of pyramidal neurons in mouse mPFC during the delay period. Behavioral performance was impaired during the learning phase but not after the mice were well trained. Delay-period mPFC activity appeared to be more important in memory retention than in inhibitory control, decision-making, or motor selection. Furthermore, endogenous delay-period mPFC activity showed more prominent modulation that correlated with memory retention and behavioral performance. Thus, properly regulated mPFC delay-period activity is critical for information retention during learning of a WM task.

Identifying the workhorse of working memory

Working memory allows us to keep behaviorally relevant information in mind over a short period of time. Liu et al. trained mice to remember a smell for a short period after it had been removed. Manipulating nerve cell activity in the mouse medial prefrontal cortex during this period interfered with the mice's performance when learning what they were supposed to do when they then smelled the same or a different odor. Once the animals were well trained on the task, the same manipulations did not affect performance.

Science, this issue p. 458

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