Connectionists: 2 papers on hippocampus, microcircuits and associative memory

[Cutsuridis, Vassilis]

Cutsuridis V, Cobb S, Graham BP. (2009). Encoding and retrieval in a model of the hippocampal CA1 microcircuit. Hippocampus, in press

The article can be found in 
http://www.cs.stir.ac.uk/~vcu/papers/CutCobGra2009Hippo.pdf

Its NEURON source code can be found in
http://senselab.med.yale.edu/modeldb/ShowModel.asp?model=123815


ABSTRACT

It has been proposed that the hippocampal theta rhythm (4-7 Hz) can contribute to memory formation by separating encoding (storage) and retrieval of memories into different functional half-cycles (Hasselmo et al. (2002) Neural Comput 14:793-817). We investigate, via computer simulations, the biophysical mechanisms by which storage and recall of spatio-temporal input patterns are achieved by the CA1 microcircuitry. A model of the CA1 microcircuit is presented that uses biophysical representations of the major cell types, including pyramidal (P) cells and four types of inhibitory interneurons: basket (B) cells, axo-axonic (AA) cells, bistratified (BS) cells and oriens lacunosum-moleculare (OLM) cells. Inputs to the network come from the entorhinal cortex (EC), the CA3 Schaffer collaterals and medial septum. The EC input provides the sensory information, whereas all other inputs provide context and timing information. Septal input provides timing information for phasing storage and recall. Storage is accomplished via a local STDP mediated hetero-association of the EC input pattern and the incoming CA3 input pattern on the CA1 pyramidal cell target synapses. The model simulates the timing of firing of different hippocampal cell types relative to the theta rhythm in anesthetized animals and proposes experimentally confirmed functional roles for the different classes of inhibitory interneurons in the storage and recall cycles (Klausberger et al., (2003, 2004) Nature 421:844-848, Nat Neurosci 7:41-47). Measures of recall performance of new and previously stored input patterns in the presence or absence of various inhibitory interneurons are employed to quantitatively test the performance of our model. Finally, the mean recall quality of the CA1 microcircuit is tested as the number of stored patterns is increased.

 
KEYWORDS: CA1 microcircuit model; storage and recall; pyramidal cell; basket cell; bistratified cell; OLM cell; axo-axonic cell; STDP

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Cutsuridis V, Wennekers T. (2009). Hippocampus, microcircuits, and associative memory. Neural Networks, in press

The article can be found in 
http://www.cs.stir.ac.uk/~vcu/papers/CutWenNN2009.pdf


ABSTRACT
The hippocampus is one of the most widely studied brain region. One of its functional roles is the storage and recall of declarative memories. Recent hippocampus research has yielded a wealth of data on network architecture, cell types, the anatomy and membrane properties of pyramidal cells and interneurons, and synaptic plasticity. Understanding the functional roles of different families of hippocampal neurons in information processing, synaptic plasticity and network oscillations poses a great challenge but also promises deep insight into one of the major brain systems. Computational and mathematical models play an instrumental role in exploring such functions. In this paper, we provide an overview of abstract and biophysical models of associative memory with particular emphasis on the operations performed by the diverse (inter)neurons in encoding and retrieval of memories in the hippocampus.

KEYWORDS: Hippocampus; Microcircuit; Associative memory; Hebb; STDP; Interneurons; Rhythms
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