Dissociation of morphological and physiological changes associated with long-term memory in aplysia.

Neurite outgrowth is a process commonly thought to contribute to long-term learning by formation of new synaptic contacts. The behavioral effects of long-term sensitization training in Aplysia were restricted to the trained side of the animal as were changes in strength of the sensorimotor synapse. In contrast, training produced varicosity formation on both sides of the animal. Appositions with follower neurons, however, were enhanced only on the trained side. The dissociation of structural and functional correlates suggests that key regulatory steps are downstream from outgrowth, possibly in the targeting of new processes and activation of new synapses.