Abstract
The neural structures that support the retention of memories over time has been a subject of intense research in cognitive neuroscience. However, recently much attention has turned to pattern separation, the putative process by which memories are stored as unique representations that are resistant to confusion. It remains unclear, however, to what extent these two processes can be neurally dissociated. The trial-unique delayed nonmatching-to-location (TUNL) task was developed to assess spatial working memory and pattern separation function using trial-unique locations on a touch-sensitive screen (Talpos, McTighe, Dias, Saksida, & Bussey, 2010). Using this task, Talpos et al. (2010) showed that lesions of the hippocampus led to both impairments with a 6s delay, and impairments in pattern separation. The present study shows that lesions of the medial prefrontal cortex lead to a different pattern of effects: impairment at the same, 6s delay, but no hint of impairment in pattern separation. In addition, rats with medial prefrontal lesions were more susceptible to interference in this task. When compared with previously published results, these data show that whereas the prefrontal cortex and hippocampus likely interact in the service of working memory across a delay, only the hippocampus and not the medial prefrontal cortex is essential for pattern separation.
Highlights
The neural structures that support the retention of memories over time has been a subject of intense research in cognitive neuroscience
The TUNL task is similar to delayed non-matching to position (DNMTP) in that two locations are used during a given trial, any of the thirteen alternative locations can serve as the correct stimulus on choice
Performance was stable across three blocks of testing (three sessions/block repeated measures ANOVA F(1,8) = 2.44, p = 0.22) with no effect of lesion on percent correct F(1,8) = 0.01, p = 0.93 and no lesion  session interaction F(1,8) = 0.29, p = 0.75).medial prefrontal cortex (mPFC) impaired accuracy in the large separation with 6-s delay (LWD) condition (Fig. 5)
Summary
The neural structures that support the retention of memories over time has been a subject of intense research in cognitive neuroscience. Researchers have become increasingly interested in the putative process of pattern separation, through which memories are stored as unique representations that are resistant to confusion (Clelland et al, 2009; Gilbert, Kesner, & DeCoteau, 1998; Yassa & Stark, 2011). It remains unclear, to what extent these two processes can be neurally dissociated. To what extent these two processes can be neurally dissociated To achieve this aim, both memory across a delay and pattern separation must be assessed using the same procedure. More selective dentate gyrus lesions could impair memory in a separation-dependent manner (Gilbert, Kesner, & Lee, 2001); CA3 lesions, in contrast, did not produce the same separation-dependent deficit,
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