The spike-timing dependence of plasticity

Abstract

In spike-timing-dependent plasticity (STDP), the order and precise temporal interval between presynaptic and postsynaptic spikes determine the sign and magnitude of long-term potentiation (LTP) or depression (LTD). STDP is widely utilized in models of circuit-level plasticity, development, and learning. However, spike timing is just one of several factors (including firing rate, synaptic cooperativity, and depolarization) that govern plasticity induction, and its relative importance varies across synapses and activity regimes. This review summarizes this broader view of plasticity, including the forms and cellular mechanisms for the spike-timing dependence of plasticity, and, the evidence that spike timing is an important determinant of plasticity in vivo.

Figure 1. Spike timing-dependent plasticity

A, Induction of STDP by pairing presynaptic spikes and associated EPSPs with postsynaptic spikes. bAP, back-propagating spike. B, Pre-leading-post spiking drives LTP, while post-leading-pre spiking drives LTD. Pre- or postsynaptic spikes alone do not alter synapse strength. From Feldman, 2000. C, STDP in hippocampal cell culture. Each symbol is one neuron. From Bi and Poo, 1998.

Figure 2. STDP exists in different forms

Selected examples illustrating each form are shown schematically. A, Hebbian STDP that is equally balanced between LTP and LTD. 1, Froemke et al., 2002. 2, Fino et al. 2008. B, Hebbian STDP that is biased towards LTD. 3, Celikel et al., 2004. 4, Froemke et al., 2002. C, Anti-Hebbian STDP that contains both LTP and LTD. 5, Fino and Venance, 2005. 6, Letzkus et al. 2006. D, Anti-Hebbian STDP that contains only LTD (anti-Hebbian LTD). 6, Han et al., 2000. 7, Lu et al., 2007. 8. Safo and Regehr, 2008.

Figure 3. Plasticity is interdependent on spike timing, firing rate, and depolarization

A, STDP at L5-L5 pyramid unitary synapses as a function of firing rate. Based on Sjöström et al., 2001. B, Joint firing rate-and timing-dependence for this same synapse modeled using a phenomenological multi-factor STDP rule (points show data, Sjöström et al., 2001; lines show model, Clopath et al., 2010). C, The LTP component of Hebbian STDP requires dendritic depolarization provided by synaptic cooperativity. Data are from distal synapses on L5 pyramidal cells (Δt= +10 ms) (Sjöström and Häusser, 2006). Open and filled symbols show inputs with weak and strong cooperativity, respectively.

Figure 4. Cellular mechanisms for timing dependence of plasticity

A, Biochemical signaling pathways for major forms of STDP. N and A, NMDA and AMPA receptors. Red, depolarization. For mGluR-CB1-LTD, the proposed presynaptic coincidence detector is in green, and the postsynaptic coincidence detector is in blue. A, astrocyte. Signals conveying pre- and postsynaptic spike timing in each model are labeled. B, Dendritic plasticity zones based on efficiency of bAP propagation through the dendrites.

Figure 5. Recent evidence for STDP in vivo

A, Stimulus-timing dependent plasticity of face perception in humans. Subjects classified a series of morphed face images as being “more like face A” or “more like face B”. Sequential A→B or B→A pairing (Δt = 20 ms) biased perception toward the earlier-presented face, with a dependence on Δt similar to Hebbian STDP. From McMahon and Leopold, 2012. B, STDP induced by visual motion stimuli in Xenopus optic tectum. Simulated motion consisting of three rapidly flashed bars was presented within the receptive field of a tectal neuron (Δt = 17 ms between bars). Bars 1 and 3 were adjusted to evoke subthreshold PSPs, while bar 2 evoked spikes. Simulated motion training caused bar 1 and 2-evoked synaptic currents to increase, but bar 3-evoked synaptic currents to decrease, consistent with Hebbian STDP. No plasticity occurred when bar 2 did not evoke spikes (not shown). From Mu and Poo, 2006. C, STDP synchronizes β-LN firing in the locust olfactory system. Odors normally evoke β-LN spikes synchronized with the trough of the local field potential (LFP). Injecting current in a β-LN to phase-delay spikes (left) induces LTP at Kenyon cell→β-LN synapses, thus phase-advancing future odor-evoked spikes (middle). Spike phase shifts bidirectionally depending on Δt during conditioning, consistent with STDP (right). From Cassenaer and Laurent, 2007.