2 research outputs found
Theta-gamma cross-frequency coupling enables covariance between distant brain regions
Cross-frequency coupling (CFC) is thought to play an important role in
communication across distant brain regions. However, neither the mechanism of
its generation nor the influence on the underlying spiking dynamics is well
understood. Here, we investigate the dynamics of two interacting distant
neuronal modules coupled by inter-regional long-range connections. Each
neuronal module comprises an excitatory and inhibitory population of quadratic
integrate-and-fire neurons connected locally with conductance-based synapses.
The two modules are coupled reciprocally with delays that represent the
long-range conduction time. We applied the Ott-Antonsen ansatz to reduce the
spiking dynamics to the corresponding mean field equations as a small set of
delay differential equations. Bifurcation analysis on these mean field
equations shows inter-regional conduction delay is sufficient to produce CFC
via a torus bifurcation. Spike correlation analysis during the CFC revealed
that several local clusters exhibit synchronized firing in gamma-band
frequencies. These clusters exhibit locally decorrelated firings between the
cluster pairs within the same population. In contrast, the clusters exhibit
long-range gamma-band cross-covariance between the distant clusters that have
similar firing frequency. The interactions of the different gamma frequencies
produce a beat leading to population-level CFC. We analyzed spike counts in
relation to the phases of the macroscopic fast and slow oscillations and found
population spike counts vary with respect to macroscopic phases. Such firing
phase preference accompanies a phase window with high spike count and low Fano
factor, which is suitable for a population rate code. Our work suggests the
inter-regional conduction delay plays a significant role in the emergence of
CFC and the underlying spiking dynamics may support long-range communication
and neural coding.Comment: 13 pages, 4 figure
Phase Dependent Sign Changes of GABAergic Synaptic Input Explored In-Silicio and In-Vitro
Abstract. Inhibitory interactions play a crucial role in the synchronization of neuronal activity. Here we investigate the effect of GABAergic PSPs on spike timing in cortical neurons that exhibit an oscillatory modulation of their membrane potential. To this end we combined numerical simulations with in-vitro patch-clamp recordings from layer II/III pyramidal cells of the rat visual cortex. Special emphasis was placed on exploring how the reversal potential of the GABAergic synaptic currents (EGABA) and the phase relations of the PSPs relative to the oscillation cycles affect the timing of spikes riding on the depolarizing peaks of the oscillations. The simulations predicted: (1) With EGABA more negative than the oscillation minima PSPs are hyperpolarizing at all phases and thus delay or prevent spikes. (2) With EGABA being more positive than the oscillation maxima PSPs are depolarizing in a phase-independent way and lead to a phase advance of spikes. (3) In the intermediate case where EGABA lies within oscillation maxima and minima PSPs are either hyper- or depolarizing depending on their phase relations to the Vm oscillations and can therefore either delay or advance spikes. Experiments conducted in this most interesting last configuration with biphasic PSPs agreed with the model predictions. Additional theoretical investigations revealed the effect of these PSP induced shifts in spike timing on synchronization in neuronal circuits. The results suggest that GABAergic mechanisms can assume highly specific timing functions in oscillatory networks