Structure and Plasticity of the Hebbian Synapse: The Cascading Events for Memory Storage
Ted L. Petit University of Toronto
One of the basic tenets of information storage is that repetitive activation induces a change in the number or structure of synapses, altering synaptic efficacy such that future information traverses the synapse more readily. This hypothesis was postulated by Hebb to underlie functions such as learning and memory ( Hebb, 1949). At the time of Hebb's proposal, however, there was little evidence to suggest that synapses were capable of change, either anatomically or physiologically. Technological advances since that time, particularly in electrophysiology and electron microscopy, have confirmed that synapses are, indeed, quite plastic, changing their structure and function in response to a number of stimuli and events. Current research is now focusing not on whether synapses change, but on how they change.
This chapter focuses on research examining the structural plasticity of the synapse and the series of events that lead to the anatomical storage of information. I provide a brief overview of the components of the synapse, discuss how these components change under various conditions, and outline a proposed sequence by which synapses could alter their structure to store memories.
A brief review of the basic components of the mammalian central nervous system (CNS) synapse is in order. The typical synapse consists of an axonal component (the presynaptic element) contacting a dendrite or