E9 Oscillations and neuronal synchronization

Topic

The cortical network consists of neuronal populations that, by behaving as mutually coupled phase oscillators, can synchronize their activity, thereby generating oscillatory rhythms observable at the macroscopic level within the network: the delta, theta, alpha, beta, and gamma bands.

The Kuramoto model—previously used to describe pathological synchronization in the cortical network—reduces each oscillating element of the network to a single phase variable characterized by an intrinsic natural frequency and a coupling to other phases in the network, where the coupling strength varies periodically based on the phase difference between elements. In its mean-field formulation, the Kuramoto model introduces an order parameter—a synchronization metric that summarizes the overall synchronization of the cortical network: the greater the mutual synchronization among the network's oscillating elements, the higher this order parameter becomes.

At the circuit level, the excitatory-inhibitory pair within the Wilson-Cowan model of the cortical network can enter an oscillatory regime, generating, for instance, a rhythm in the gamma band. The frequency of this oscillatory regime depends on both the time constants of the excitatory and inhibitory populations and the reciprocal connection strengths between them: the faster the time constants and the stronger the reciprocal connections, the higher the frequency of the network's oscillatory regime.

Spectral coherence in the cortical network quantifies the degree of coupling between two network signals in the frequency domain, whereas phase-amplitude coupling measures how the phase of a slow cortical oscillation modulates the amplitude of a fast cortical oscillation—a phenomenon relevant to the temporal organization of cortical activity. Taken together, it is this very cortical network—comprising oscillating elements capable of synchronization according to the Kuramoto model and excitatory-inhibitory pairs capable of entering oscillatory regimes according to the Wilson-Cowan model—that generates the macroscopically observable oscillatory rhythms, the coupling of which (across both signals and distinct frequencies) temporally organizes the activity of the entire cortical network.

ID:4267