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.
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