Hagiwara, Ruby, & Heller, 2003). Glucose still must be metabolized to generate ATP for
the hippocampus. As this happens, brain temperature increases due to the intense
metabolic activity (Heller, 2005). Homeostatic thermoregulation has been suspended
(Orem & Keeling, 1980), perhaps to allow this increase in cerebral metabolic activity.
As ATP is generated, the hippocampus becomes active and rhythmic theta waves
appear on the EEG. The pupils dilate (Rechtschaffen, 1998), perhaps indicating a change
in hippocampal energy availability. Then, the pupils become constricted (Siegel, 2005),
perhaps indicating that the hippocampus has more than enough energy to function. The
EEG becomes desynchronized as it does during wakefulness. Dreams occur (Aserinsky &
Kleitman, 1953). However, all of this brain activity is probably incidental. It likely occurs
only because of the sudden availability of ATP, and it probably uses only a small
percentage of the ATP that is generated. Thus, most of the ATP generated during REM
sleep is conserved for use during wakefulness.
Phasic REM sleep likely occurs when additional cerebral glucose is required to
meet the elevated metabolic requirements of REM sleep. The heart rate surges, arterial
blood pressure increases, respiratory activity fluctuates, and there is a momentary
increase in electrodermal activity. Blood glucose levels have already been elevated, and
glucose is transported from the body to the brain via the bloodstream. Cerebral blood
flow to the amygdala and parts of the pons, thalamus, cingulate cortex, and parietal
operculum increases significantly (Maquet, 1995; Maquet et al., 1996). These areas and
the hippocampal formation become significantly activated (Maquet, 2000). The pupils
dilate maximally (Kemp & Kaada, 1975), perhaps indicating a massive increase in ATP
preliminary draft (9/24/2006)