ConceptSTDP

Spike-Timing-Dependent Plasticity (STDP)

The principle of neurons that fire together wire together is one of the most widely quoted phrases in neuroscience and artificial intelligence. Attributed to Donald Hebb, this phrase symbolizes the process of synaptic learning. However, it is deeply misleading. Hebb's actual words were more precise. When an axon of cell A is near enough to excite cell B, some metabolic change takes place such that A's efficiency is increased. This isn't a simple co-firing rule, it implies causality. It's not enough for A and B to be active at the same time. A must help cause B to fire, and the relative timing of their spikes matters immensely.

This refinement is formalized into the more biologically plausible rule of spike-timing-dependent plasticity, or STDP, in which the precise timing between presynaptic and postsynaptic spikes determines whether a synapse is strengthened or weakened. STDP captures some details. If neuron A fires before neuron B by a few milliseconds, the synapse is strengthened. If A fires after B, it is weakened. However, even this model, though useful, fails to fully account for the complex realities of how synaptic learning occurs in the brain.

• Source: 2025-08-05 ‘Neurons That Fire Together Wire Together’ Is Wrong