What is Long-term depression?
Long-term depression (LTD) is a persistent weakening of synaptic connections following specific patterns of neural activity. It is the counterpart to long-term potentiation and is essential for learning, memory refinement, and forgetting.
How it works
LTD occurs when synapses are activated at low frequency or when presynaptic and postsynaptic activity is poorly timed. It results in reduced receptor density and decreased neurotransmitter release at the synapse. LTD is not simply the absence of learning but an active process essential for brain function: it enables the brain to prune unnecessary connections, refine neural circuits, and update stored information. Without LTD, old memories and habits would never be modified.
Applied example
Motor skill refinement depends on LTD in the cerebellum: when a tennis player adjusts their serve, the synapses supporting the old movement pattern are weakened (LTD) while those supporting the new pattern are strengthened (LTP). Without LTD, the old motor program would persist alongside the new one.
Why it matters
Long-term depression is the brain’s mechanism for unlearning and updating, making it as essential to adaptive behavior as its more famous counterpart, long-term potentiation.
