Dendritic and Axonal Propagation Delays Determine Emergent Structures of Neuronal Networks with Plastic Synapses

Mojtaba Madadi Asl,Peter A Tass,Alireza Valizadeh

doi:10.1038/srep39682

Abstract

Spike-timing-dependent plasticity (STDP) modifies synaptic strengths based on the relative timing of pre- and postsynaptic spikes. The temporal order of spikes turned out to be crucial. We here take into account how propagation delays, composed of dendritic and axonal delay times, may affect the temporal order of spikes. In a minimal setting, characterized by neglecting dendritic and axonal propagation delays, STDP eliminates bidirectional connections between two coupled neurons and turns them into unidirectional connections. In this paper, however, we show that depending on the dendritic and axonal propagation delays, the temporal order of spikes at the synapses can be different from those in the cell bodies and, consequently, qualitatively different connectivity patterns emerge. In particular, we show that for a system of two coupled oscillatory neurons, bidirectional synapses can be preserved and potentiated. Intriguingly, this finding also translates to large networks of type-II phase oscillators and, hence, crucially impacts on the overall hierarchical connectivity patterns of oscillatory neuronal networks.

Highlights

The functional effects of Spike-timing-dependent plasticity (STDP), and in particular its relation to the synchronization in neuronal networks have led to contradicting results
From the theory of delayed coupled oscillators it is well-known that the total propagation delay, i.e. the sum of the dendritic and axonal propagation delays, determine the synchronization tendency of the coupled neuronal oscillators[52,53,54,55,56], which is predicted by their phase response curve (PRC)[57,58]
Dendritic and axonal propagation delays play a dual role in the networks of coupled neurons when the synapses are modified through STDP: Their difference enters into the synaptic modification rule and their sum determines the synchronizing/desynchronizing nature of the connection[59]

Summary

Introduction

The functional effects of STDP, and in particular its relation to the synchronization in neuronal networks have led to contradicting results. An intermediate effect has been reported showing that in the presence of propagation delays, STDP promotes the self-organization of recurrent networks into mixture states at the border between randomness and synchrony[12] This latter result depends mainly on the imbalance of potentiation and depression for small time lags between presynaptic and postsynaptic spikes, and a small difference between dendritic and axonal propagation delay times, assuming the axonal delays are larger[40]. Dendritic and axonal propagation delays play a dual role in the networks of coupled neurons when the synapses are modified through STDP: Their difference enters into the synaptic modification rule and their sum determines the synchronizing/desynchronizing nature of the connection[59]. We show that our results have significant implications to the hierarchical organization of connectivity patterns in networks of oscillatory neurons

Methods

Results

Conclusion