Synaptic Plasticity

STDP as a stable local learning rule

This module keeps the computation local and deterministic while exposing the timing-dependent learning rule through linked charts and a typed state model.

STDP curve

Timing window

dt = 0LTPLTD

Weight evolution

Synaptic strength across pairings

initialSpike pair

Outcome

Learning direction

LTP

Final weight

0.7911

Delta per pair

0.0049

Hebbian rule

"Neurons that fire together wire together" is only the broad idea. STDP says the exact timing decides whether the synapse should strengthen or weaken.

What happened

With deltaT=10 ms, the presynaptic spike occurs before the postsynaptic spike. That timing is interpreted as causal, so the synapse potentiates.
STDP is local and biologically plausible. Backpropagation is far more powerful, but it relies on a non-local error signal that real synapses do not obviously receive.

Biological basis

  • NMDA receptors behave like coincidence detectors because they need presynaptic glutamate and postsynaptic depolarization together.
  • Pre-before-post timing can trigger calcium conditions that favor CaMKII signaling and AMPA receptor insertion.
  • Post-before-pre timing changes calcium dynamics enough to favor phosphatases and synaptic weakening instead.
  • Making LTD slightly stronger than LTP helps stabilize the network and prevents runaway excitation.