Mathematical model of synaptic plasticity: II. Habituation.

A mathematical model of the phenomenon of habituation as a homosynaptic depression of the amount of transmitter release is proposed. The model is based on the physiological studies of habituation in invertebrates and in the spinal cord of vertebrates, where a single synapse has been isolated and some of the physiological mechanisms of this process have been elucidated. The model simulates the following properties of habituation: (1) reduced amount of transmitter release attributed to a repetitive stimulus through changes in the membrane permeability to Ca2+ ions; (2) spontaneous recovery by rest; (3) the amplitude and frequency dependence of habituation; (4) modulation of habituation: sensitization, through an increase in membrane Ca2+ permeability, and presynaptic inhibition, through a reduced depolarization of the physiological stimulus; (5) long-term habituation attributed to repetitive trials of habituation and spontaneous recovery.