long-term potentiation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Repeated presynaptic stimulation of a nerve, either naturally or in vitro, that results in the long-lasting increased strength of a synapse and is thought to be necessary for learning and memory formation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun neuroscience A long-lasting (hours in vitro, weeks to months in vivo) increase, typically in amplitude, of the response of a postsynaptic neuron to a particular pattern of stimuli from a presynaptic neuron.