As sleep deepens, subjects enter a third sleep stage, N3. They are either spontaneous or occur in response to sudden sensory stimuli 6. Often K-complexes co-occur with sleep spindles or may even trigger them 5. Their brief negative peak in the EEG seems to be a signature of neuronal hyperpolarization, while its initial positive component depends on excitation of neurons. K-complexes are variable patterns of sudden bursts consisting mostly of a high voltage diphasic slow wave, especially in N2. They have a waxing and a waning component and last for about 1 sec at a time 3, 4. Spindles are rhythmic bursts of EEG activity that oscillate at a frequency between 12–15 Hz (classically named as sigma band). The following, second sleep stage (N2) is characterized by the occurrence of sleep spindles and K-complexes in the EEG signal. The first light sleep stage (N1) is a state of drowsiness and of early loss of consciousness, physiologically characterized by a decreasing low voltage EEG frequency (2–7 Hz) 2. Our aim is to exploit the higher localization accuracy of magnetoencephalography (MEG) to shed new light on the spatial distribution of oscillatory features in non-REM sleep stages. These oscillatory patterns of the sleeping brain have been described mostly using EEG. In each sleep stage, the brain is characterized by specific patterns of oscillatory activity. Sleep occurs periodically following a rather strict circadian rhythm and is itself a highly dynamic event, characterized by re-occurring and alternating phases of circa 80–120 minutes each, during which different polysomnographic events can be recorded 1. Brain activity both during wakefulness and sleep is characterized by fluctuations in neuronal responses and rhythmic activation at various time scales.
0 kommentar(er)
