Modulating STDP Balance Impacts the Dendritic Mosaic.

Nicolangelo Iannella,Thomas Launey

doi:10.3389/fncom.2017.00042

Abstract

The ability for cortical neurons to adapt their input/output characteristics and information processing capabilities ultimately relies on the interplay between synaptic plasticity, synapse location, and the nonlinear properties of the dendrite. Collectively, they shape both the strengths and spatial arrangements of convergent afferent inputs to neuronal dendrites. Recent experimental and theoretical studies support a clustered plasticity model, a view that synaptic plasticity promotes the formation of clusters or hotspots of synapses sharing similar properties. We have previously shown that spike timing-dependent plasticity (STDP) can lead to synaptic efficacies being arranged into spatially segregated clusters. This effectively partitions the dendritic tree into a tessellated imprint which we have called a dendritic mosaic. Here, using a biophysically detailed neuron model of a reconstructed layer 2/3 pyramidal cell and STDP learning, we investigated the impact of altered STDP balance on forming such a spatial organization. We show that cluster formation and extend depend on several factors, including the balance between potentiation and depression, the afferents' mean firing rate and crucially on the dendritic morphology. We find that STDP balance has an important role to play for this emergent mode of spatial organization since any imbalances lead to severe degradation- and in some case even destruction- of the mosaic. Our model suggests that, over a broad range of of STDP parameters, synaptic plasticity shapes the spatial arrangement of synapses, favoring the formation of clustered efficacy engrams.

Highlights

Activity-dependent changes in the firing properties of cortical neurons can arise from modifying the spatial arrangement of afferent fibers converging onto dendrites and their corresponding synaptic strengths (Poirazi et al, 2003a; De Roo et al, 2008; McBride et al, 2008)
In the case of Gütig’s nonlinear spike timingdependent plasticity (STDP), synapses compete both spatially and temporally to control the timing of somatic and/or dendritic spike generation. This competition is believed to take the form of a spatio-temporal winner-take-all process that leads to the formation of synaptic efficacy clusters
A key feature of Gütig’s nonlinear STDP rule is the presence of the exponent μ. This parameter controls the weight dependence of the rule and can be interpreted as a parameter that controls the degree of competition, since μ = 0 corresponds to the additive STDP and exhibits strong competition (Song et al, 2000; Song and Abbott, 2001); while μ = 1 recovers the multiplicative STDP rule, a rule known to display stable yet weak competition dynamics

Summary

Introduction

Activity-dependent changes in the firing properties of cortical neurons can arise from modifying the spatial arrangement of afferent fibers converging onto dendrites and their corresponding synaptic strengths (Poirazi et al, 2003a; De Roo et al, 2008; McBride et al, 2008). The pattern of activity conveyed by such afferents can either strengthen (Bliss and Gardner-Medwin, 1973; Bliss and Lomo, 1973) or weaken (Kirkwood and Bear, 1994) stimulated synapses. Such physiological changes are believed to represent a substrate for learning and memory; the mechanisms responsible for the spatial arrangement have yet to be fully elucidated

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Results

Discussion

Conclusion