Figure 6.

Increased excitability in model explains observed changes as anesthesia lightens

(A) Top: schematic representation of the simulated network, consisting of 13 × 13 local cell assemblies. Cell assemblies are composed of excitatory and inhibitory integrate-and-fire neurons and are sketched on the left those with increased excitability (stronger synaptic self-excitation, red circles) and on the right the ones with reference excitability in the rest of the grid. The internal square shows the portion of the network used for the analysis. Middle: bifurcation diagram showing the different activity regimes displayed by spiking neuron network simulations as the level g_a of the firing rate adaptation and the rate v_ext of incoming excitatory spikes from other (external) areas are changed. To model anesthesia fading, these parameters are changed according to the depicted black line connecting the low-firing asynchronous (LAS) and the slow wave state. The arrows point to the parameter combinations used in the rest of the figure. Bottom: coefficient of variation of Up-Down cycles (circles) and frequency of waves (f_w, squares) measured in simulations along the above black trajectory.

(B) Representative average and single-channel log(MUA) in the simulated network for low wave frequency/high CV (top, “deep-like”), and high frequency/low CV (bottom, “light-like”) modeling deep and light levels of anesthesia, respectively.

(C and D) Distributions of time lag arrays of spontaneously occurring activation waves in the model network in the plane (PC₁, PC₂) as in Figures 3A and 3B for in vivo recordings. Model networks in both the deep-like and the light-like conditions are shown (panel C and D, respectively). Colored dots highlight the wavefronts belonging to the modes of propagations singled out in bottom panels, relying on k-means clustering as in Figure 3C. For the “light-like” case (panel D) three representative groups of wavefronts were selected; these included the points centered at the yellow stars (see STAR Methods for details).

(E) Average log(MUA) of the five leading (red) and five following (blue) channels (thin) and averages (thick) around the Down-Up transitions for all modes shown in panel C, for the “deep-like” (left) and “light-like” (right) conditions.

(F) Percentage of explained variance as a function of the number of PCs for the TLMs extracted from the simulated data.

(G) Frequency of the activation waves versus the CV of the Up-Down cycles for the simulated data obtained from 10 equally-sized nonoverlapping intervals of time.