The frontal predominance in human EEG delta activity after sleep loss decreases with age.

Sleep loss has marked and selective effects on brain wave activity during subsequent recovery sleep. The electroencephalogram (EEG) responds to sleep deprivation with a relative increase in power density in the delta and theta range during non-rapid eye movement sleep. We investigated age-related changes of the EEG response to sleep deprivation along the antero-posterior axis (Fz, Cz, Pz, Oz) under constant routine conditions. Both healthy young (20-31 years) and older (57-74 years) participants manifested a significant relative increase in EEG power density in the delta and theta range after 40 h of sleep deprivation, indicating a sustained capacity of the sleep homeostat to respond to sleep loss in ageing. However, the increase in relative EEG delta activity (1.25-3.75 Hz) following sleep deprivation was significantly more pronounced in frontal than parietal brain regions in the young, whereas such a frontal predominance was diminished in the older volunteers. This age-related decrease of frontal delta predominance was most distinct at the beginning of the recovery sleep episode. Furthermore, the dissipation of homeostatic sleep pressure during the recovery night, as indexed by EEG delta activity, exhibited a significantly shallower decline in the older group. Activation of sleep regulatory processes in frontal brain areas by an extension of wakefulness from 16 to 40 h appears to be age-dependent. These findings provide quantitative evidence for the hypothesis that frontal brain regions are particularly vulnerable to the effects of elevated sleep pressure ('prefrontal tiredness') and ageing ('frontal ageing').