The other side of the engram: experience-driven changes in neuronal intrinsic excitability

KEY POINTS * In addition to synaptic plasticity, which confers neurons with the ability to modify the strength of individual synapses, nerve cells also possess forms of intrinsic plasticity

(changes in intrinsic excitability), which affect largest ensembles of synapses and might affect the whole cell. This form of plasticity might endow neurons with an additional capacity to

store information. * Different learning tasks induce changes in intrinsic excitability in several vertebrate and invertebrate species. In many cases, these changes manifest as reductions in

spike threshold, spike accommodation and amplitude of burst-evoked afterhyperpolarization, all of which point to the modulation of K+ channels as one potential underlying mechanism. * Forms

of experience-dependent plasticity other than learning also elicit intrinsic plasticity, which share similar mechanisms as learning-mediated plastic changes. These forms of experience

include adaptive and maladaptive states, such as seizures. * Studies in cell culture and brain slices have shown that it is possible to study intrinsic excitability _in vitro_. These studies

have pointed to a series of K+, Ca2+ and Na+ conductances as possible molecular substrates of the plastic changes. * The signal transduction cascades mediating the conductance changes that

seem to be crucial for intrinsic plasticity remain unknown for most model systems. Ca2+/calmodulin-dependent protein kinase II and other kinases, the action of G-proteins, and the release of

intracellular Ca2+ have been proposed, but the definitive experiments remain to be reported. * Many changes remain to be answered in this nascent field. What is the relationship between

intrinsic and synaptic plasticities, particularly in cases when both phenomena seem to co-exist? What is the duration of intrinsic plasticity? Does it really function to encode information?

If so, what kind of memories could it store? These and many other issues should generate as much attention of intrinsic excitability changes as there has been on synaptic plasticity.

ABSTRACT Modern theories of memory storage have largely focused on persistent, experience-dependent changes in synaptic function such as long-term potentiation and depression. But in

addition to these synaptic changes, certain learning tasks produce enduring changes in the intrinsic excitability of neurons by changing the function of voltage-gated ion channels, a change

that can produce broader, even neuron-wide changes in synaptic throughput. We will consider the evidence for persistent changes in intrinsic neuronal excitability — what we will call

intrinsic plasticity — that is produced by training in behaving animals and by artificial patterns of activation in brain slices and neuronal cultures. These intrinsic changes might function

as part of the engram itself, or as a related phenomenon such as a trigger for the consolidation or adaptive generalization of memories. Access through your institution Buy or subscribe

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ENGRAM NEURONS: ENCODING, CONSOLIDATION, RETRIEVAL, AND FORGETTING OF MEMORY Article Open access 28 June 2023 INHIBITORY PLASTICITY SUPPORTS REPLAY GENERALIZATION IN THE HIPPOCAMPUS Article

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CAS  PubMed  Google Scholar  Download references ACKNOWLEDGEMENTS Thanks to H. Nishiyama, A. Sdrulla and J. H. Shin for helpful suggestions. This work was supported by the USPHS and the

Develbiss Fund. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Neuroscience, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, 21205, Maryland,

USA Wei Zhang & David J. Linden Authors * Wei Zhang View author publications You can also search for this author inPubMed Google Scholar * David J. Linden View author publications You

can also search for this author inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to David J. Linden. RELATED LINKS RELATED LINKS DATABASES LocusLink PubMed FURTHER INFORMATION

ENCYCLOPEDIA OF LIFE SCIENCES long-term depression and depotentiation long-term potentiation GLOSSARY * SYNAPTIC STRENGTH The amplitude of the postsynaptic potential that is evoked by a

single shock to a population of axons. * ASSOCIATIVITY The property of long-term potentiation (LTP) whereby weak stimulation of a synaptic input, which will not elicit an increase in

synaptic strength, can lead to the onset of LTP if strong stimulation is simultaneously applied to an independent input to the same postsynaptic cell. * INPUT SPECIFICITY The property of

long-term potentiation whereby strong synaptic stimulation only elicits an increase in synaptic strength at the activated pathway, leaving every other input unaffected. * THROUGHPUT The

probability of a single synapse evoking an action potential. * STATOCYST Organ that mediates balance in many invertebrates. It consists of a fluid-filled sac that contains statoliths (minute

calcareous particles) that stimulate sensory cells and help indicate position when the animal moves. * PNEUMOSTOME A small opening in the mantle of gastropods through which air passes. *

HABITUATION The cessation of a response upon repeated presentations of a stimulus. * SENSITIZATION The unspecific augmentation of a behavioural response to a stimulus after the animal has

been exposed to an injurious stimulus. * INPUT RESISTANCE The voltage change that is elicited by the injection of current into a cell, divided by the amount of current injected. * GLABELLA

The smooth area between the eyebrows just above the nose. * AFTERHYPERPOLARIZATION The membrane hyperpolarization that follows the occurrence of an action potential. * OPERANT CONDITIONING

Form of conditioning in which the subject learns from the consequences of its actions, thereby modifying its behaviour. * ACCOMMODATION The cessation of spike firing despite constant

depolarization above firing threshold. * INWARD PLATEAU CURRENT A current that inactivates slowly, resulting in a sustained depolarization. * DELAYED OUTWARD-RECTIFIER K+ CURRENT A slowly

activating and very slowly inactivating voltage-gated K+ conductance that preferentially passes K+ out of the cell. * REFRACTORY PERIOD The period after a spike during which a neuron cannot

fire a new action potential. * MACROPATCHES Giant membrane patches that are commonly obtained to study membrane currents of cells that are too large to record with conventional patch-clamp

methods. * CURRENT–VOLTAGE RELATION A plot of the changes in ionic current as a function of membrane voltage. * POPULATION SPIKE The summated action potential of the postsynaptic neurons

that respond to a given stimulus as recorded with an extracellular electrode. * SCHAFFER COLLATERALS Axons of the CA3 pyramidal cells of the hippocampus that form synapses with the apical

dendrites of CA1 neurons. * THETA BURSTS Rhythmic neural activity with a frequency of 4–8 Hz. * DYNAMIC CLAMPING Recording configuration in which the current that is injected into the cell

mimics a specific pattern of synaptic activation. * METAPLASTICITY Term that has been coined to refer to the higher-order plasticity of synaptic plasticity. In other words, how synaptic

activity or other stimuli modify the properties of synaptic plasticity itself. RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Zhang, W., Linden, D. The

other side of the engram: experience-driven changes in neuronal intrinsic excitability. _Nat Rev Neurosci_ 4, 885–900 (2003). https://doi.org/10.1038/nrn1248 Download citation * Issue Date:

01 November 2003 * DOI: https://doi.org/10.1038/nrn1248 SHARE THIS ARTICLE Anyone you share the following link with will be able to read this content: Get shareable link Sorry, a shareable

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