A 1949 guess — neurons that fire together wire together — was later proven right

Donald Hebb proposed that when one neuron repeatedly helps fire another, the connection between them physically strengthens over time. It was a theoretical postulate in a psychology textbook, not an experiment, until decades later when scientists found the actual mechanism, long-term potentiation, in living brain tissue.

— Donald O. Hebb, The Organization of Behavior — 1949
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