Local patterns of sleep and wakefulness

It is now well established that sleep and wakefulness are locally regulated. In particular, slow waves, the hallmarks of non-rapid eye movement (NREM) sleep, display a clear regional modulation, depending on experience and learning during the preceding waking period. Local “slow wave”-like oscillations can also occur during wakefulness, increasing with time spent awake and as a function of regional experience-dependent activations. Such oscillations reflect the occurrence of neuronal off periods and may account for cognitive impairment and task-specific performance errors during sleep deprivation. Although initially thought to occur only in NREM sleep, slow waves and associated off periods have also been documented in REM sleep, and local decreases and increases in slow-wave activity in posterior brain areas have been shown to determine whether one is unconscious or dreaming across behavioral states (REM and NREM sleep). Extreme forms of state dissociation, in which islands of wakefulness and sleep simultaneously coexist in different brain areas, can be observed in some sleep disorders and may contribute to explain some of the symptoms that characterize these conditions.