The ability of different groups of cortical neurons to engage in causal interactions that are at once differentiated
and integrated results in complex dynamic patterns. Complexity is low during periods of unconsciousness (deep
sleep, anesthesia, unresponsive wakefulness syndrome) in which the brain tends to generate a stereotypical pattern consisting of alternating active and silent periods of neural activity—slow oscillations— and is high during
wakefulness. But how is cortical complexity built ...
The ability of different groups of cortical neurons to engage in causal interactions that are at once differentiated
and integrated results in complex dynamic patterns. Complexity is low during periods of unconsciousness (deep
sleep, anesthesia, unresponsive wakefulness syndrome) in which the brain tends to generate a stereotypical pattern consisting of alternating active and silent periods of neural activity—slow oscillations— and is high during
wakefulness. But how is cortical complexity built up? Is it a continuum? An open question is whether cortical
complexity can vary within the same brain state. Here we recorded with 32-channel multielectrode arrays from
the cortical surface of the mouse and used both spontaneous dynamics (wave propagation entropy and functional
complexity) and a perturbational approach (a variation of the perturbation complexity index) to measure complexity at different anesthesia levels. Variations in anesthesia level within the bistable regime of slow oscillations
(0.1–1.5 Hz) resulted in a modulation of the slow oscillation frequency. Both perturbational and spontaneous
complexity increased with decreasing anesthesia levels, in correlation with the decrease in coherence of the underlying network. Changes in complexity level are related to, but not dependent on, changes in excitability. We
conclude that cortical complexity can vary within a single brain state dominated by slow oscillations, building
up to the higher complexity associated with consciousness.
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