Presynaptic facilitation as a mechanism for behavioral sensitization in Aplysia.

Sensitization is an elementary form of nonassociative learning, related to behavioral arousal, in which a strong stimulus facilitates a reflex response. Studies of the neural circuit of the gill-withdrawal reflex in the isolated abdominal ganglion on Aplysia indicate that short-term sensitization is due to presynaptic facilitation. The facilitation results in a sudden increase in the amount of neurotransmitter released by the sensory neurons at their synapses with motor neurons.