Phasic modulation of cortical high-frequency oscillations by pedunculopontine neurons.

Brain states are dynamically shaped by distinct neuronal systems across the brain as a result of an interplay between their intrinsic activity and the environmental demand. Subsets of brainstem and forebrain structures influence the manifestation of specific brain states (e.g., sleep or wakefulness) and contribute to their cyclic alternation. Recent evidence, however, shows that such functional partition is not observed in the brainstem, where neuronal subpopulations engage in particular patterns of activity that contribute to the emergence of phasic components during the cortical slow oscillations. Cholinergic neurons of the pedunculopontine nucleus are functionally associated with the induction of the waking state but discharge during the phase of the slow oscillations that support neuronal activity. Here, we discuss the impact of the phasic signals arising from subcortical structures on the modulation of cortical slow oscillations and their functional significance.