SynapticRedistribution

An effect that LTP sometimes has upon ShortTermDepression (it’s not that the synapses are redistributed over space, it’s that the “synaptic efficacy” is redistributed over time). Before and after undergoing LTP, the synapse may be tested with both high-frequency and low-frequency spike trains. In neocortex, LTP potentiates the first EPSPs? of a high-frequency spike train, but leaves the steady-state EPSP? amplitude the same. However, for low-frequency test trains, the steady-state EPSP? amplitude is potentiated too. See (Markram and Tsodyks ‘96) for such an experiment.

It is not known if all forms of neocortical potentiation also evoke synaptic redistribution (rather than only some protocols), or if LTD will reverse the synaptic redistribution.

Mechanisms

The mechanism of synaptic redistribution is not certain, but a hypothesis is that there is an increase in presynaptic probability of transmitter release. For the first few spikes in a high-frequency train, or for all the spikes in a low-frequency train, this causes an increase in EPSP? amplitude. This depletes the pool of readily releasable vesicles more, though, so that later spikes in a high-frequency train don’t show the same potentiation.

Functions

Synaptic redistribution could be used for all sorts of things. One specific proposal has been pattern learning; see PatternLearningWithSynapticRedistribution.

Papers

Experimental papers

• Markram and Tsodyks ‘96: Redistribution of synaptic efficacy between neocortical pyramidal neurons
• Sejnowski ‘96: Synapses get smarter. review of Markram and Tsodyks ‘96
• Buonomano ‘99: Distinct functional types of associative long-term potentiation in neocortical and hippocampal pyramidal neurons

Papers that might connect it to map plasticity

• Finnerty et al ‘99: Sensory experience modifies short-term dynamics of neocortical synapses

Functions

General

• Markram and Tsodyks ‘96: Redistribution of synaptic efficacy: A mechanism to generate infinite synaptic input diversity from a homogenous population of neurons without changing absolute synaptic efficacies simply points out that given a spike train of similarly sized inputs, the rank ordering of EPSPs? can be much changed by changing synaptic efficacy
• Sejnowski ‘96: Synapses get smarter. review of Markram and Tsodyks ‘96

Refs

• Buonomano DV. Distinct functional types of associative long-term potentiation in neocortical and hippocampal pyramidal neurons. J Neurosci. 1999 Aug 15;19(16):6748-54.
• Finnerty, G. T., Roberts, L. & Connors, B. W. Sensory experience modifies short-term dynamics of neocortical synapses. Nature 400, 367-371 (1999).
• Markram H, Tsodyks M. Redistribution of synaptic efficacy between neocortical pyramidal neurons. Nature. 1996 Aug 29;382(6594):807-10.
• H Markram and M Tsodyks. Redistribution of synaptic efficacy: A mechanism to generate infinite synaptic input diversity from a homogenous population of neurons without changing absolute synaptic efficacies. Journal of Physiology-Paris, Volume 90, Issues 3-4, 1996, Pages 229-232.
• Sejnowski TJ. Synapses get smarter. Nature. 1996 Aug 29;382(6594):759-60.

See also LongTermPlasticity.

CategoryPlasticity

CategorySynaptic