The mechanisms for pattern completion and pattern separation in the hippocampus

By E. T. Rolls. 2013

521 citations recorded by the source corpus.

The mechanisms for pattern completion and pattern separation are described in the context of a theory of hippocampal function in which the hippocampal CA3 system operates as a single attractor or autoassociation network to enable rapid, one-trial, associations between any spatial location (place in rodents, or spatial view in primates) and an object or reward, and to provide for completion of the whole memory during recall from any part. The factors important in the pattern completion in CA3 together with a large number of independent memories stored in CA3 include a sparse distributed representation which is enhanced by the graded firing rates of CA3 neurons, representations that are independent due to the randomizing effect of the mossy fibers, heterosynaptic long-term depression as well as long-term potentiation in the recurrent collateral synapses, and diluted connectivity to minimize the number of multiple synapses between any pair of CA3 neurons which otherwise distort the basins of attraction. Recall of information from CA3 is implemented by the entorhinal cortex perforant path synapses to CA3 cells, which in acting as a pattern associator allow some pattern generalization. Pattern separation is performed in the dentate granule cells using competitive learning to convert grid-like entorhinal cortex firing to place-like fields. Pattern separation in CA3, which is important for completion of any one of the stored patterns from a fragment, is provided for by the randomizing effect of the mossy fiber synapses to which neurogenesis may contribute, by the large number of dentate granule cells each with a sparse representation, and by the sparse independent representations in CA3. Recall to the neocortex is achieved by a reverse hierarchical series of pattern association networks implemented by the hippocampo-cortical backprojections, each one of which performs some pattern generalization, to retrieve a complete pattern of cortical firing in higher-order cortical areas.

Subfields: Cellular and Molecular Neuroscience, Cognitive Neuroscience, Developmental Neuroscience

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Citations in the corpus

Pattern separation in the hippocampus through the eyes of computational modeling (2017, background): “…Neher et al. (2015) developed a computational model of EC-DG-CA3-CA1 hippocampal subregions and studied the effect of grid-like properties of EC inputs (Hafting, Fyhn, Molden, Moser, & Moser, 2005; Moser, Kropff, & Moser, 2008; Rolls, 2013) on pattern separation (Neher, Cheng, & Wiskott, 2015).”
Cognitive impairment in schizophrenia: aetiology, pathophysiology, and treatment (2023, background): “As inhibitory signalling is crucial for appropriate memory separation [272], disinhibition could promote the aberrant associations and working memory de ﬁ cits that are evident in people with schizophrenia [270].”
Spatial representations of granule cells and mossy cells of the dentate gyrus (2017, background): “However, the storage capacity of such a distributed memory system is limited and susceptible to interference if the stored patterns are too similar to each other (McNaughton and Morris, 1987; Rolls, 2013).”