spike-timing-dependent plasticity

Spike-timing-dependent plasticity, or STDP, is a rule for how a connection between two brain cells grows stronger or weaker based on the precise order and timing of their electrical pulses. Brain cells, called neurons, talk to each other across tiny junctions called synapses, and they fire off brief electrical blips known as spikes. STDP says that what matters is not just whether two neurons fire together, but who fires first and by how many thousandths of a second. Think of two people clapping: if one consistently claps a hair-beat before the other, their rhythm locks in; if the timing keeps slipping the other way, the partnership falls apart.

The key twist is that the sign of the change flips depending on the order. If the sending neuron fires a few milliseconds before the receiving neuron, the synapse is strengthened — the sender looks like it helped cause the receiver's spike, so the link is rewarded. If the sender fires just after the receiver, the synapse is weakened, because the sender clearly arrived too late to have mattered. This tiny timing window, usually within about twenty milliseconds, lets the brain pick out genuine cause-and-effect chains and is widely thought to be one of the physical mechanisms behind learning and memory.