Influence of external input on waxing and waning of neuronal network oscillations

Introduction

Experimental observations have reported modulation of cortical oscillations as phases of high synchronization (waxing) followed by periods of reduced synchronization (waning) [1–3]. Although the phenomenon is present in almost all frequency bands, it is still not understood how this is driven. Here we study whether this phenomenon can occur in a network of inhibitory (I) and excitatory (E) cells and what effect external inputs have.

Methods

Using NEURON, we model a network of N _e excitatory and N _i inhibitory cells such that N _e /N _i = 4. The cells have a single compartment, and include passive channels and voltage dependent Na⁺, K⁺ channels. Synaptic connections are random, projecting GABA synapses from I to I and I to E cells and AMPA synapses from E to E and E to I cells. To stimulate the network, each cell receives a baseline of current and a stream of spikes delivered at random intervals across the simulated period.

Results

We show that in a stable oscillatory network, waxing and waning occurs without the need for other synaptic mechanisms than the spike generating K⁺ and Na⁺ channels. The phenomenon can be modulated by changing the characteristics of the external input, such as number of spikes, mean inter-spike interval, randomness and whether E or I cells receive the external input. See figures 1 and 2.

Figure 1

Raster plots of E (top) and I (middle) populations, during waxing and waning of a beta oscillation, and firing rate histograms (bottom).

Figure 2

Wavelet transform of the activity in the E population for the same time period as shown in figure 1.