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Neurobiol Learn Mem. 2016 Mar;129:99-106. doi: 10.1016/j.nlm.2016.01.006. Epub 2016 Feb 1.

The representational-hierarchical view of pattern separation: Not just hippocampus, not just space, not just memory?

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Department of Medicine, Division of Neurology, University of British Columbia, Vancouver, Canada. Electronic address:
Department of Psychology, University of Cambridge, Cambridge, UK.
Department of Psychology, University of Cambridge, Cambridge, UK; The Brain and Mind Institute, Western University, London, ON, Canada; Molecular Medicine Research Group, Robarts Research Institute, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada; Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada; MRC and Wellcome Trust Behavioural and Clinical Neuroscience Institute, University of Cambridge, Downing St, Cambridge CB2 3EB, UK.


Pattern separation (PS) has been defined as a process of reducing overlap between similar input patterns to minimize interference amongst stored representations. The present article describes this putative PS process from the "representational-hierarchical" perspective (R-H), which uses a hierarchical continuum instead of a cognitive modular processing framework to describe the organization of the ventral visual perirhinal-hippocampal processing stream. Instead of trying to map psychological constructs onto anatomical modules in the brain, the R-H model suggests that the function of brain regions depends upon what representations they contain. We begin by discussing a main principle of the R-H framework, the resolution of "ambiguity" of lower level representations via the formation of unique conjunctive representations in higher level areas, and how this process is remarkably similar to definitions of PS. Work from several species and experimental approaches suggest that this principle of resolution of ambiguity via conjunctive representations has considerable explanatory power, leads to wide possibilities for experimentation, and also supports some perhaps surprising conclusions.


Hippocampus; Memory; Pattern separation; Perception; Perirhinal cortex; Representational–hierarchical

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