A graded hyperpolarization or increase in the electrical potential across the membrane of a postsynaptic neuron, occurring in response to a signal transmitted across a synapse (1) by a presynaptic neuron and reducing the propensity of the postsynaptic neuron to initiate a nerve impulse. Also called postsynaptic inhibition. See also action potential, resting potential. Compare excitatory postsynaptic potential. IPSP abbrev.