Abstract
Structural plasticity governs the long-term development of synaptic connections in the neocortex. While the underlying processes at the synapses are not fully understood, there is strong evidence that a process of random, independent formation and pruning of excitatory synapses can be ruled out. Instead, there must be some cooperation between the synaptic contacts connecting a single pre- and postsynaptic neuron pair. So far, the mechanism of cooperation is not known. Here we demonstrate that local correlation detection at the postsynaptic dendritic spine suffices to explain the synaptic cooperation effect, without assuming any hypothetical direct interaction pathway between the synaptic contacts. Candidate biomolecular mechanisms for dendritic correlation detection have been identified previously, as well as for structural plasticity based thereon. By analyzing and fitting of a simple model, we show that spike-timing correlation dependent structural plasticity, without additional mechanisms of cross-synapse interaction, can reproduce the experimentally observed distributions of numbers of synaptic contacts between pairs of neurons in the neocortex. Furthermore, the model yields a first explanation for the existence of both transient and persistent dendritic spines and allows to make predictions for future experiments.
Highlights
The structure of neocortical networks of neurons changes in time: new synapses are formed, maturate, and eventually are pruned again, in the adult as well as in the developing animal [1,2], for recent reviews see [3,4,5]
We propose a model for structural plasticity that relies on local processes at the dendritic spine
We conclude that the local dendritic mechanisms that we assume suffice to explain the cooperative synapse formation in the neocortex
Summary
The structure of neocortical networks of neurons changes in time: new synapses are formed, maturate, and eventually are pruned again, in the adult as well as in the developing animal [1,2], for recent reviews see [3,4,5]. The three studies [17,18,19] reported the distributions of numbers of synaptic contacts for different intra-cortical synapses in rat somatosensory cortex. Fares et al [20] subsequently analyzed whether the reported distributions could result from random and independent synaptic contact formation, given a set of potential sites (close appositions) between axons and dendrites of reconstructed cells. As they showed, independent formation of synaptic contacts alone cannot explain the distributions. In addition a cooperative pruning mechanism, by which synaptic contacts that constitute a single synapse stabilize each other, is required to explain the observed distributions
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