Spike Timing-Dependent Plasticity Presented by: Arash Ashari Woodin MA, Ganguly K, and Poo MM. Coincident pre- and postsynaptic activity modifies GABAergic synapses by postsynaptic changes in Cl- transporter activity, Neuron 39: 807820, 2003. Dan Y, Poo MM. Spike timing-dependent plasticity: from synapse to perception. Physiol Rev. 2006 Jul;86(3):1033-48. Review. Rao, R. and Sejnowski, T. Spike-timing-dependent Hebbian plasticity as temporal difference learning. Neural Comput, 13(10):22212237, 2001. Slides mostly from: www.mbi.osu.edu 1
Outline Neuron, Synapse, Depolarization and Hyperpolarization Long-Term Potentiation and Depression (LTP and LTD) Spike Timing-Dependent Plasticity (STDP) A Mathematical Model for STDP Discussion 2 3 4 Dendrite: 1. Spatial Summation 2. Temporal Summation
Biogenic Amines Dopamine, Histamine Neuropeptides LHRH, Proctolin NMDA, GABAA are typical receptors Glumatergic: Excitatory GABAergic: Inhabitatory 9 Excitatory (EPSP) or Inhibitory (IPSP) 10 Depolarization: Influx of Na and Ca cations This causes a spike (Action Potential a pulse-like wave of voltage) Hyperpolarization: Outflux of K cations or influx of Cl anion11
Long-Term Synaptic Enhancement Long-Term Potentiation (LTP) ~ Rapid and sustained increase in synaptic efficacy following a brief but potent stimulus Best studied in the hippocampus Induction of LTP occurs at the postsynaptic site and requires the conjunction of pre and post-synaptic activity On the order of hours, days or longer 12 13 Long-term Synaptic Enhancement The mechanisms underlying LTP remain
controversial The existence of Long Term Depression (LTD) A possible way to study LTP might be Spike Time Dependent Plasticity (STDP) 14 Spike Time Dependent Plasticity 15 Synaptic Plasticity Hebbs Postulate: When an axon of cell A... excites cell B and
repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells so that A's efficiency as one of the cells firing B is increased. In standard Hebbian learning, a synaptic weight is increased if presynaptic and postsynaptic neuron are `simultaneously' active. If neurons communicate by spikes, the concept of simultaneity implies the pre- and postsynaptic spikes occur within some time window. Theory predicts that these time windows could have two phases corresponding to an increase (potentitiation) or decrease (depresseion) of the synaptic weight depending on the relative timing of pre- and postsynaptic spike. Such asymmetric learning rules with two phases have been found in recent experiments. 16
Spike Time Dependent Plasticity Weakening Presynaptic Cell Excitatory Synapse Strengthening t Postsynaptic Cell t
17 What do experiments show? % Change in PostSynaptic Current Presynaptic Cell Excitatory Synapse Postsynaptic Cell t = tpost - tpre 18 Guo-qiang Bi and Mu-ming Poo, J. of Neuroscience, December 1998
So, what are the STDP rules? 19 L. F. Abbott and S. B. Nelson, 2000 Nature Review Similar results: Karmarkar and Bunomano, 2002; Abarbanel et. al. 2003; Kitijima and Hara, 2000 (ms) 20
0.1 I peak ( M / ms) .08 .06 LTP B N
.04 +/- LTD .02 0 -50 LTD 0
LTP 50 100 t (ms) 150 LTD 200 21 A Mathematical Model for STDP
Presynaptic Cell V ' Vrest V g ex Eex V m gex is PLASTIC Excitatory Synapse
Postsynaptic Cell g ' ex g ex / ex V Postsynaptic Membrane Potential Vrest Postsynaptic Membrane Resting Potential gex Excitatory Synaptic Conductance Eex Excitatory Synaptic Reversal Potential m Membrane Potential decay time constant ex gex decay time constant
22 Song, Miller, Abbott Model for STDP A exp t / if t 0 F t A exp t / if t 0 Strengthening Weakening t t t
t F(%) F(%) A+ M ' M / P ' P / P(t) t = tpost - tpre
t t M(t) A- 23 Updating P and M When Presynaptic cell fires, Update P When Postsynaptic cell fires, Update M
Presynaptic Cell P P A M M A Excitatory Synapse F(%) F(%) Postsynaptic Cell A+
P(t) t t M(t) A- 24 Updating gex Synaptic conductance gex is updated when there is a presynaptic action potential at excitatory synapse When Presynaptic cell fires
g a g a M g max When Postsynaptic cell fires g a g a P g max g ex g ex g a ga Denotes the peak synaptic conductance (the synaptic conductance immediately after an isolated presynaptic spike) ADDITIVE RULE for Synaptic Modification 25 Putting things into perspective
Vrest V g ex Eex V ' V g ' ex g ex / ex m P ' P / M ' M / When Presynaptic cell fires, When Postsynaptic cell fires,
1. P P A 1. M M A 2. g a g a M g max 2. g a g a P g max
3. g ex g ex g a Strengthening Weakening Presynaptic Cell t Postsynaptic Cell t
Excitatory Synapse t t 26 In the real world Multiple Synapses 1 postsynaptic neuron How about inhibitory synapses!! Hence, the equation for the postsynaptic neuron changes to include the inhibitory synapses V
' V rest V g ex Eex V g in Ein V m g ' in g in / in gin Inhibitory Synaptic Conductance Ein Inhibitory Synaptic Reversal Potential in gin decay time constant
27 1000 Excitatory Synapses 1000 P functions, but only ONE M function!!! 200 Inhibitory Synapses Postsynaptic Cell Presynaptic Excitatory cell fires,
Postsynaptic cell fires, 1. P[1...1000] P[ j ] A 1. 2. g [1...1000] g [ j ] M g max 2. 3.
g ex g ex g [1...1000] M M A g [1...1000] g [ j ] P[ j ] g max Presynaptic Inhibitory cell fires, 1. g in g in g in 28 Discussion How LTP and LTD occur? Can STDP underlie Memory and
Learning? How? Correlated activity can occur purely by chance, rather should be learned than reflecting a causal relationship that STDP as a Reinforcement Learning/ Temporal Difference Learning 29 References Woodin MA, Ganguly K, and Poo MM. Coincident pre- and postsynaptic activity modifies GABAergic synapses by postsynaptic changes in Cltransporter activity, Neuron 39: 807820, 2003. Dan Y, Poo MM. Spike timing-dependent plasticity: from synapse to perception. Physiol Rev. 2006 Jul;86(3):1033-48. Review. Rao, R. and Sejnowski, T. Spike-timing-dependent Hebbian plasticity as
temporal difference learning. Neural Comput, 13(10):22212237, 2001. Song, S., Miller, K. D., & Abbott, L. F. (2000). Competitive Hebbian learning through spike-timing-dependent synaptic plasticity. Nature Neuroscience, 3, 919-926. http://en.wikipedia.org/wiki/ 30 Thank you Any Questions? 31
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