To assess dynamic changes in brain function throughout the sleep-wake cycle, CBF was
measured with H2(15)O and PET in 37 normal male volunteers: (i) while awake prior
to sleep onset; (ii) during Stage 3-4 sleep, i.e. slow wave sleep (SWS); (iii) during
rapid eye movement (REM) sleep; and (iv) upon waking following recovery sleep. Subjects
were monitored polysomnographically and PET images were acquired throughout the course
of a single night. Stage-specific contrasts were performed using statistical parametric
mapping. Data were analysed in repeated measures fashion, examining within-subject
differences between stages [pre-sleep wakefulness-SWS (n = 20 subjects); SWS-post-sleep
wakefulness (n = 14); SWS-REM sleep (n = 7); pre-sleep wakefulness-REM sleep (n =
8); REM sleep-post-sleep wakefulness (n = 7); pre-sleep wakefulness-post-sleep wakefulness
(n = 20)]. State dependent changes in the activity of centrencephalic regions, including
the brainstem, thalamus and basal forebrain (profound deactivations during SWS and
reactivations during REM sleep) are consistent with the idea that these areas are
constituents of brain systems which mediate arousal. Shifts in the level of activity
of the striatum suggested that the basal ganglia might be more integrally involved
in the orchestration of the sleep-wake cycle than previously thought. State-dependent
changes in the activity of limbic and paralimbic areas, including the insula, cingulate
and mesial temporal cortices, paralleled those observed in centrencephalic structures
during both REM sleep and SWS. A functional dissociation between activity in higher
order, heteromodal association cortices in the frontal and parietal lobes and unimodal
sensory areas of the occipital and temporal lobes appeared to be characteristic of
both SWS and REM sleep. SWS was associated with selective deactivation of the heteromodal
association areas, while activity in primary and secondary sensory cortices was preserved.
SWS may not, as previously thought, represent a generalized decrease in neuronal activity.
On the other hand, REM sleep was characterized by selective activation of certain
post-rolandic sensory cortices, while activity in the frontoparietal association cortices
remained depressed. REM sleep may be characterized by activation of widespread areas
of the brain, including the centrencephalic, paralimbic and unimodal sensory regions,
with the specific exclusion of areas which normally participate in the highest order
analysis and integration of neural information. Deactivation of the heteromodal association
areas (the orbital, dorsolateral prefrontal and inferior parietal cortices) constitutes
the single feature common to both non-REM and REM sleep states, and may be a defining
characteristic of sleep itself. The stages of sleep could also be distinguished by
characteristic differences in the relationships between the basal ganglia, thalamic
nuclei and neocortical regions of interest.