A learning rule, which is based on physiological observations of brains,
neurons, and their
synapses and
axons.
From
Donald Hebb's book
The Organization of Behaviour:
"When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased."
This forms the basis of
associative learning, and is often shortened to: "If it fires together, it wires together."