Sensitization in Aplysia: restoration of transmission in synapses inactivated by long-term habituation.

Long-term habituation of a simple withdrawal reflex in Aplysia leads to an inactivation of synaptic transmission between identified sensory and gill motor neurons that persists for more than 3 weeks. A single sensitizing stimulus rapidly reactivates both the depressed behavioral response and the inactivated synaptic transmission. Thus sensitization, a simple competitive form of learning, provides a mechanism whereby changing environmental demands can rapidly override the long-term memory of habituation.