Hebbian learning rule: synaptic weight changes driven by relative spike timing
Spike-timing dependent plasticity (STDP) is a biological learning rule discovered by Markram et al. (1997) and Bi & Poo (1998): if a presynaptic neuron fires just before a postsynaptic neuron (Δt > 0), the synapse is strengthened (long-term potentiation, LTP). If the order is reversed (Δt < 0), the synapse is weakened (long-term depression, LTD). The weight change follows ΔW = A+ · exp(-Δt/τ+) for LTP and ΔW = -A- · exp(Δt/τ-) for LTD. This asymmetric Hebbian rule allows neurons to learn causal temporal relationships and underlies sequence learning and memory formation.