A persistent cellular change in a single modulatory neuron contributes to associative long-term memory

Curr Biol. 2003 Jun 17;13(12):1064-9. doi: 10.1016/s0960-9822(03)00380-4.


Most neuronal models of learning assume that changes in synaptic strength are the main mechanism underlying long-term memory (LTM) formation. However, we show here that a persistent depolarization of membrane potential, a type of cellular change that increases neuronal responsiveness, contributes significantly to a long-lasting associative memory trace. The use of a model invertebrate network with identified neurons and known synaptic connectivity had the advantage that the contribution of this cellular change to memory could be evaluated in a neuron with a known function in the learning circuit. Specifically, we used the well-understood motor circuit underlying molluscan feeding and showed that a key modulatory neuron involved in the initiation of feeding ingestive movements underwent a long-term depolarization following behavioral associative conditioning. This depolarization led to an enhanced single cell and network responsiveness to a previously neutral tactile conditioned stimulus, and the persistence of both matched the time course of behavioral associative memory. The change in the membrane potential of a key modulatory neuron is both sufficient and necessary to initiate a conditioned response in a reduced preparation and underscores its importance for associative LTM.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Association Learning / physiology*
  • Electrophysiology
  • Feeding Behavior / physiology
  • Lymnaea / physiology*
  • Membrane Potentials / physiology*
  • Memory / physiology*
  • Nerve Net / physiology*
  • Neural Networks, Computer
  • Time Factors