Illustration of long-term potentiation and long-term depression. During long-term potentiation, the postsynaptic neuron is stimulated : a presynaptic signal stimulates a postsynaptic neuron (1), after potentiation, stimulation is more efficient : the postsynaptic neuron is stimulated by less action potentials (2), or for an equal presynaptic action potential, the postsynaptic neuron is stimulated harder (3). Long-term depression reduces stimulation : for a given presynaptic signal (4), stimulation is weaker (5), or even absent, the synapse is called silent (6).