CiteULike: awooga's stdp

Dendritic mechanisms controlling spike-timing-dependent synaptic plasticity.

BM Kampa — 2008-06-06T14:57:55-00:00

Trends in neurosciences, Vol. 30, No. 9. (September 2007), pp. 456-463.

The ability of neurons to modulate the strength of their synaptic connections has been shown to depend on the relative timing of pre- and postsynaptic action potentials. This form of synaptic plasticity, called spike-timing-dependent plasticity (STDP), has become an attractive model for learning at the single-cell level. Yet, despite its popularity in experimental and theoretical neuroscience, the influence of dendritic mechanisms in the induction of STDP has been largely overlooked. Several recent studies have investigated how active dendritic properties and synapse location within the dendritic tree influence STDP. These studies suggest the existence of learning rules that depend on firing mode and subcellular input location, adding unanticipated complexity to STDP. Here, we propose a new look at STDP that is focused on processing at the postsynaptic site in the dendrites, rather than on spike-timing at the cell body.

Functional Significance of Long-Term Potentiation for Sequence Learning and Prediction

Abbott — 2008-03-28T10:43:33-00:00

Cereb. Cortex, Vol. 6, No. 3. (1 May 1996), pp. 406-416.

Population coding, where neurons with broad and overlapping firing rate tuning curves collectively encode information about a stimulus, is a common feature of sensory systems. We use decoding methods and measured properties of NMDA-mediated LTP induction to study the impact of long-term potentiation of synapses between the neurons of such a coding array. We find that, due to a temporal asymmetry in the induction of NMDA-mediated LTP, firing patterns in a neuronal array that initially represent the current value of a sensory input will, after training, provide an experienced-based prediction of that input instead. We compute how this prediction arises from and depends on the training experience. We also show how the encoded prediction can be used to generate learned motor sequences, such as the movement of a limb. This involves a novel form of memory recall that is driven by the motor response so that it automatically generates new information at a rate appropriate for the task being performed. 10.1093/cercor/6.3.406

Extending the effects of spike-timing-dependent plasticity to behavioral timescales.

PJ Drew — 2006-08-01T06:40:05-00:00

Proc Natl Acad Sci U S A, Vol. 103, No. 23. (6 June 2006), pp. 8876-8881.

Activity-dependent modification of synaptic strengths due to spike-timing-dependent plasticity (STDP) is sensitive to correlations between pre- and postsynaptic firing over timescales of tens of milliseconds. Temporal associations typically encountered in behavioral tasks involve times on the order of seconds. To relate the learning of such temporal associations to STDP, we must account for this large discrepancy in timescales. We show that the gap between synaptic and behavioral timescales can be bridged if the stimuli being associated generate sustained responses that vary appropriately in time. Synapses between neurons that fire this way can be modified by STDP in a manner that depends on the temporal ordering of events separated by several seconds even though the underlying plasticity has a much smaller temporal window.

Neuromodulators control the polarity of spike-timing-dependent synaptic plasticity.

GH Seol — 2007-09-24T13:51:51-00:00

Neuron, Vol. 55, No. 6. (20 September 2007), pp. 919-929.

Near coincidental pre- and postsynaptic action potentials induce associative long-term potentiation (LTP) or long-term depression (LTD), depending on the order of their timing. Here, we show that in visual cortex the rules of this spike-timing-dependent plasticity are not rigid, but shaped by neuromodulator receptors coupled to adenylyl cyclase (AC) and phospholipase C (PLC) signaling cascades. Activation of the AC and PLC cascades results in phosphorylation of postsynaptic glutamate receptors at sites that serve as specific "tags" for LTP and LTD. As a consequence, the outcome (i.e., whether LTP or LTD) of a given pattern of pre- and postsynaptic firing depends not only on the order of the timing, but also on the relative activation of neuromodulator receptors coupled to AC and PLC. These findings indicate that cholinergic and adrenergic neuromodulation associated with the behavioral state of the animal can control the gating and the polarity of cortical plasticity.

Hebb and anti-Hebb meet in the brainstem

Sacha Nelson — 2007-10-24T13:49:28-00:00

Nat Neurosci, Vol. 7, No. 7. (July 2004), pp. 687-688.

Solving the Distal Reward Problem through Linkage of STDP and Dopamine Signaling.

Eugene M Izhikevich — 2007-01-17T21:02:55-00:00

Cereb Cortex (13 January 2007)

In Pavlovian and instrumental conditioning, reward typically comes seconds after reward-triggering actions, creating an explanatory conundrum known as "distal reward problem": How does the brain know what firing patterns of what neurons are responsible for the reward if 1) the patterns are no longer there when the reward arrives and 2) all neurons and synapses are active during the waiting period to the reward? Here, we show how the conundrum is resolved by a model network of cortical spiking neurons with spike-timing-dependent plasticity (STDP) modulated by dopamine (DA). Although STDP is triggered by nearly coincident firing patterns on a millisecond timescale, slow kinetics of subsequent synaptic plasticity is sensitive to changes in the extracellular DA concentration during the critical period of a few seconds. Random firings during the waiting period to the reward do not affect STDP and hence make the network insensitive to the ongoing activity-the key feature that distinguishes our approach from previous theoretical studies, which implicitly assume that the network be quiet during the waiting period or that the patterns be preserved until the reward arrives. This study emphasizes the importance of precise firing patterns in brain dynamics and suggests how a global diffusive reinforcement signal in the form of extracellular DA can selectively influence the right synapses at the right time.

Bidirectional activity-dependent plasticity at corticostriatal synapses.

E Fino — 2006-01-17T15:45:48-00:00

J Neurosci, Vol. 25, No. 49. (7 December 2005), pp. 11279-11287.

Corticostriatal projections originate from the entire cerebral cortex and provide the major source of glutamatergic inputs to the basal ganglia. Despite the importance of corticostriatal connections in sensorimotor learning and cognitive functions, plasticity forms at these synapses remain strongly debated. Using a corticostriatal slice preserving the connections between the somatosensory cortex and the target striatal cells, we report the induction of both non-Hebbian and Hebbian forms of long-term potentiation (LTP) and long-term depression (LTD) on striatal output neurons (SONs). LTP and LTD can be induced selectively by different stimulation patterns (high-frequency trains vs low-frequency pulses) and were evoked with similar efficiency in non-Hebbian and Hebbian modes. Combination of LTP-LTD and LTD-LTP sequences revealed that bidirectional plasticity occurs at the same SONs and provides efficient homeostatic mechanisms leading to a resetting of corticostriatal synapses avoiding synaptic saturation. The effect of temporal relationship between cortical stimulation and SON activity was assessed using spike-timing-dependent plasticity (STDP) protocols. An LTP was observed when an action potential was triggered in the striatal neuron before the cortical stimulus, and, conversely, an LTD was induced when the striatal neuron discharge was triggered after the cortical stimulation. Such STDP was reversed when compared with those described so far in other mammalian brain structures. This mechanism may be essential for the role of the striatum in learning of motor sequences in which sensory and motor events are associated in a precise time sequence.