Synaptic plasticity

Synaptic plasticity is the capacity of a neural synapse to strengthen or weaken over time in response to changes in activity. It is the cellular mechanism underlying learning and memory, and it operates across multiple timescales — from milliseconds (short-term potentiation) to years (structural remodeling). The concept, first proposed by Donald Hebb in 1949 ('neurons that fire together, wire together'), has been refined by decades of experimental work into specific biophysical mechanisms including spike-timing-dependent plasticity, long-term potentiation (LTP), and homeostatic scaling. Synaptic plasticity is not merely a biological implementation detail; it is a general principle of adaptive systems. Any system that must learn from experience — biological or artificial — must possess some form of plasticity, whether implemented in synapses, weights, or organizational structure. The failure of plasticity, as in Alzheimer's disease or saturated neural networks, is not a local malfunction but a systemic collapse of the system's capacity to adapt.