Abbott Hebbian Learning STDP Spike Synaptic Plasticity 2000

Jul 4, 2010 11:22 AM

Competitive Hebbian learning

through spike-timing-dependent

synaptic plasticity

Sen Song1, Kenneth D. Miller2 and L. F. Abbott1

Nature Neursci 2000

Hebbian models of development and learning require both activity-dependent synaptic plasticity

and a mechanism that induces competition between different synapses. One form of experimentally

observed long-term synaptic plasticity, which we call spike-timing-dependent plasticity (STDP),

depends on the relative timing of pre- and postsynaptic action potentials. In modeling studies, we

find that this form of synaptic modification can automatically balance synaptic strengths to make

postsynaptic firing irregular but more sensitive to presynaptic spike timing. It has been argued that

neurons in vivo operate in such a balanced regime. Synapses modifiable by STDP compete for

control of the timing of postsynaptic action potentials. Inputs that fire the postsynaptic neuron with short latency or that act in correlated groups are able to compete most successfully and develop strong synapses, while synapses of longer-latency or less-effective inputs are weakened.

 Although Hebbian synaptic modification

has received support from experiments on long-term potentia-

tion and depression5, much less is known about the mechanisms

that generate competition between synapses.

 Here we explore an

entirely different mechanism suggested by experimental results

on the effect of spike timing on long-term synaptic modifica-

tion11–20, in which different synapses compete for control of the

timing of postsynaptic action potentials. We show that the depen-

dence of synaptic modification on spike timing provides a mech-

anism that can lead to competitive Hebbian learning without

requiring global intracellular signaling, or preset activity or

synaptic efficacy levels.

long-term strengthening of synapses occurs if presynaptic

action potentials precede postsynaptic firing by no more than

about 50 ms. Presynaptic action potentials that follow postsy-

naptic spikes produce long-term weakening of synapses. The

largest changes in synaptic efficacy occur when the time differ-

ence between pre- and postsynaptic action potentials is small,

and there is a sharp transition from strengthening to weakening

as this time difference passes through zero. We call this form of

synaptic modification spike-timing-dependent plasticity (STDP).

See Figure 1  STDP modification function...

conductance is enhanced if presynap spike occurs right before post synapt spike...

(tau is abt 20 msec) 

DISCUSSUON

  key feature of  STDP is  competition arises in a new way... by competition for control of the

timing of postsynap potentials.

Inputs that are consistently best at predicting a postsynap response become the strongest inputs to the neuron.  CAUSALITY is a key element of STDP.  As Hebb suggested, synapses are only strengthened

if the presyn act pots  precede the pst synaptic ones.

STD automat leads to causal correlation.

Abbott Hebbian Learning STDP Spike Synaptic Plasticity 2000

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