Neurophysiology. A change in the functional properties of synapses as a result of use. Different biophysical and biochemical mechanisms underly such changes that can last from seconds to minutes (short-term plasticity) or from days to years (long-term plasticity). Synaptic strength can be increased (short-term or long-term potentiation) or decreased (short-term or long-term depression). This is achieved for example by a changed number of receptors or by a altered amount of neurotransmitter released into the synaptic cleft.