Brain, Vol. 125, No. 10, 2308-2319,
October 2002
© 2002 Oxford University Press
The process of awakening: a PET study of regional brain activity patterns mediating the re-establishment of alertness and consciousness
1 Department of Behavioral Biology, Walter Reed Army Institute of Research, Washington, DC, 2 Language Section, Voice Speech and Language Branch, National Institute on Deafness and Communication Disorders and 3 PET Imaging Section, National Institutes of Health, Bethesda, Maryland, USA
Correspondence to: T. J. Balkin, Department of Behavioral Biology, Walter Reed Army Institute of Research, Washington, DC 20307-5100, USA E-mail: thomas.balkin{at}na.amedd.army.mil
Awakening from sleep entails rapid re-establishment of consciousness followed by the relatively slow (20–30 min later) re-establishment of alertness—a temporal dissociation that facilitates specification of the physiological underpinnings of each of these facets of the awakening process. H215O PET was used to assess changes in regional cerebral blood flow (rCBF) upon awakening from stage 2 sleep. Cerebral blood flow (CBF) was most rapidly re-established in centrencephalic regions (e.g. brainstem and thalamus), suggesting that the reactivation of these regions underlies the re-establishment of conscious awareness. Across the ensuing 15 min of wakefulness, further increases in CBF were evident primarily in anterior cortical regions, suggesting that the dissipation of sleep inertia effects (post-awakening performance and alertness deficits) is effected by reactivation of these regions. Concomitant shifts in correlation patterns of regional brain activity across the post-awakening period [in particular, a waning negative correlation between prefrontal cortex and mesencephalic reticular formation (RF) activity, and a waxing positive correlation between prefrontal cortex and ventromedial caudate nucleus (CAUD) activity] suggest that the post-awakening reversal of sleep inertia effects may be mediated by more than mere reactivation—it may also involve the functional reorganization of brain activity. Conversely, stable post-awakening correlations—such as those found between the anterior cingulate cortex (ACC) and most other brain regions—may denote the pattern of functional connectivity that underlies consciousness itself.
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