Post-Tetanic Potentiation (PTP) is a form of synaptic plasticity

Synaptic plasticity

In neuroscience, synaptic plasticity is the ability of the connection, or synapse, between two neurons to change in strength in response to either use or disuse of transmission over synaptic pathways. Plastic change also results from the alteration of the number of receptors located on a synapse...

 which is short-lived and results in increased frequency with no effect on amplitude in the spontaneous postsynaptic potential

Postsynaptic potential

Postsynaptic potentials are changes in the membrane potential of the postsynaptic terminal of a chemical synapse. Postsynaptic potentials are graded potentials, and should not be confused with action potentials although their function is to initiate or inhibit action potentials...

. It usually lasts in the range of several minutes (shorter potentiations are usually referred to as 'augmentations'). PTPs are observed when synapses are stimulated with repetitive (tetanic) pulses, by means of prolonged trains of stimuli applied at high frequencies (10 Hz to 200 Hz stimuli applied for .2 seconds to 5 seconds).

PTPs are thought to result primarily from the buildup of calcium concentraion in the axon terminal of the presynaptic neuron during the stimulus train.

In some cases, depression can be observed instead of potentiation following the tetanic stimulus.