synaptic plasticity

Synaptic plasticity is the brain's ability to make the tiny connections between nerve cells stronger or weaker depending on how much they are used. A synapse is the little gap where one neuron passes a message to the next; think of it like a footpath between two houses. When that path gets used over and over, it gets worn wider and easier to travel, so the message crosses faster and more reliably. When it sits unused, it grows over with weeds and the message gets through only weakly. The connection is not fixed at birth — it is constantly being remodeled by your own activity.

This tuning of connections is widely believed to be how learning and memory physically happen inside the brain. A common rule of thumb is "cells that fire together, wire together": when two neurons are active at the same moment again and again, the synapse between them strengthens, a change called long-term potentiation. The opposite, weakening a rarely-used connection, is called long-term depression. By turning the volume up on useful pathways and down on useless ones, the brain encodes a new skill, a face, or a fact as a lasting pattern of strong and weak synapses — which is why practice makes a memory stick and why forgetting can let a connection fade.