Long-term potentiation

Meaning: LTP is a long-lasting strengthening of an existing synapse after repeated, high-frequency stimulation. Afterward, the same presynaptic signal produces a larger postsynaptic response. In the hippocampus, glutamate binds AMPA and NMDA receptors. NMDA receptors open only when glutamate is bound and the postsynaptic cell is already depolarized, so they detect co-activation of both cells. Ca²⁺ then enters, and the postsynaptic cell strengthens the connection, for example by adding or sensitizing AMPA receptors. This matches Hebb's idea that cells that fire together wire together, and it is a main example of synaptic plasticity.

On the MCAT: A passage may describe stimulating a hippocampal pathway repeatedly and measuring a growing postsynaptic response, or blocking NMDA receptors and showing that LTP and learning are impaired. You may be asked to predict that more co-activation gives a stronger synapse, or to link LTP to memory formation and consolidation. A related contrast is long-term depression (LTD), a lasting weakening of a synapse.

Common confusion: LTP is not the growth of new neurons, and it is not a change in the type of neurotransmitter. It is a change in the strength of existing connections. It is also not long-term memory itself. It is the proposed cellular mechanism that helps support memory.