The precise timing of neuronal-spike discharges is believed to be important for coding of information. The ability of various neuron types to time their action potentials with millisecond precision depends largely on the several parameters of the neurons and the underlying network through which the neurons communicate. To name a few, coordination of the activity of the neurons can be affected by the response function of the neurons, heterogeneity in firing rates, pattern of the synaptic efficacies, balance between excitation and inhibition, and the delay in communication between the neurons. Although the effects of delayed interaction are often neglected when the intrinsic dynamics is much slower than the coupling delay, they can be crucial otherwise. A unique feature of delay-coupled oscillators is that their synchronization depends on the oscillatory frequency. We show that this feature can lead to transitions between synchrony and asynchrony in delayed coupled neuronal networks when the level of input to the network changes. Moreover, since the impact of a neuronal network to downstream neurons increases when spikes are synchronous, networks with delayed connections can serve as gatekeeper layers mediating the firing transfer to other regions. The switch between active and inactive coupling channels depends on the input level, originating from sensory stimulus or from extrinsic control sources. Since the changes in the synaptic strengths are also determined by the timing of activity of the pre- and post-synaptic neurons, the evolution of the structure of the neuronal networks can be affected by the communication delay based on the possible effects of the delays on the relative spike timing of the neurons. We argue that some of the reported theoretical and simulation results on the effect of the spike-timing-dependent plasticity on the structure of neuronal networks can be changed when transmission delays are taken into account.
School of Cognitive Sciences, Institute for Research in Fundamental Sciences (IPM),
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