Facilitation, depression, and posttanic potentiation may briefly modify synaptic transmission but cannot provide the basis for memories or other manifestations of behavioral plasticity that persist for months, weeks, or years. Some patterns of synaptic activity in the central nervous system produce a prolonged increase in synaptic strength known as long-term potentiation (PLP), while other patterns of activity cause a prolonged decrease in synaptic strength, known as long-term depression.