Memory (Mechanisms Other than LTP)

Abstract

Synaptic plasticity is not the exclusive mode of memory storage, and persistent regulation of voltage‐gated ionic channels also participates in information storage. Long‐term changes in neuronal excitability have been reported in several brain areas following learning. Synaptic activation of glutamate receptors initiates long‐lasting modification in neuronal excitability at the pre‐ or postsynaptic side, that is, in the axon, soma and dendrites of central neurons. Intrinsic plasticity is expressed in virtually all neuronal types including principal cells and interneurons. It is mediated by changes in the expression level or biophysical properties of voltage‐gated ion channels in the membrane and can affect many different neuronal operations such as dendritic integration and action potential generation and propagation. Similarly to synaptic plasticity, long‐lasting intrinsic plasticity is bidirectional and expresses a certain level of input or cell specificity. Synaptic and intrinsic plasticities not only share common learning rules and induction pathways but also contribute in synergy with these synaptic changes to the formation of a coherent mnesic engram.

Key Concepts:

  • Synaptic plasticity is a major mode of memory storage.

  • Persistent regulation of voltage‐gated ionic channels also participates in information storage following learning.

  • Synaptic activation of glutamate receptors initiates long‐lasting modification in neuronal excitability at the pre‐ or postsynaptic side.

  • Intrinsic plasticity is mediated by changes in the expression level or biophysical properties of voltage‐gated ion channels in the membrane.

  • Intrinsic plasticity can affect many different neuronal operations such as dendritic integration, action potential generation, action potential shape, action potential propagation and backpropagation.

  • Synaptic and intrinsic plasticities share common learning rules and induction pathways.

  • Synaptic and intrinsic plasticities contribute in synergy to the formation of a coherent mnesic engram.

Keywords: E–S potentiation; LTP; dendrites; synaptic integration

Figure 1.

Facilitation of the input–output function through the regulation of postsynaptic receptors or voltage‐gated channels. (a) Persistent potentiation of synaptic transmission is characterised by enhanced postsynaptic current (EPSC). At the initial segment, the excitatory postsynaptic potential (EPSP) is large enough to cross the action potential (AP) threshold and to elicit a postsynaptic spike. (b) The same result is obtained if the AP threshold is hyperpolarized through the regulation of voltage‐gated channels located at the cell body and/or axon initial segment. Note that here the synaptic current remains unchanged. (c) Enhanced amplification of the EPSP by voltage‐gated channels located in the dendrite allows the generation of a postsynaptic AP without change in the EPSC.

Figure 2.

Local and global changes in intrinsic neuronal excitability. (a) Regulation of ion channels in the dendrites (blue dots) will preserve input specific changes. (b) Modulation of ion channels in the axon (blue dots) will globally affect the excitability of all inputs.

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Debanne, Dominique, and Campanac, Emilie(Aug 2014) Memory (Mechanisms Other than LTP). In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021398.pub2]