Pet-Scan Brain Imaging of Hyper Arousal In Insomnia

By Dr. Gregg D. Jacobs - December 8, 2004

Insomnia is now conceptualized as a disorder of excessive brain arousal, in which a stronger trait-like wake drive (e.g., arousal system) disturbs the homeostatic drive for sleep. This excessive strength in the wake drive not only makes it harder for insomniacs to sleep; it also mitigates the effects of sleep loss so that insomniacs do not show the same deleterious responses to sleep deprivation as seen in normal sleepers. Despite widespread agreement that insomnia is characterized by an abnormally strong wake drive, the brain mechanisms of this hyper arousal are not known.

In a recent study in the American Journal of Psychiatry (161: 2126-2129), a group of researchers at the University of Pittsburgh School of Medicine led by Dr. Eric Nofzinger used PET scans to assess brain metabolism in insomnia patients compared to normal sleepers while awake and asleep.

The subjects for this study consisted of 7 insomniacs and 13 normal sleepers (a small sample of insomniacs). EEG sleep was measured in all subjects as well as brain metabolic activity using a PET scanner for 20 minutes after sleep onset and on the following morning after awakening (because it is not easy to sleep in a PET scanner, sleep is likely to be altered relative to sleep in the home environment or sleep lab).

The EEG sleep recordings showed that normal sleepers fell asleep in 14 minutes, while insomniacs required only 5 more minutes to fall asleep. Similarly, insomniacs exhibited virtually the same sleep efficiency as normal sleepers at over 90%. These findings suggest that this small sample of insomniacs were, objectively, not insomniacs- they were normal sleepers. Thus, the relevance of the study findings to insomniacs is uncertain. On the PET scans, insomniacs showed smaller declines in brain metabolism (e.g., smaller declines in wake drive or “arousal”) relative to normal sleepers from wake to sleep. During wakefulness, insomniacs showed lower brain metabolism (less arousal) in the frontal areas of the brain than normals, which the researchers suggest demonstrate a basis for the complaints of daytime fatigue in insomniacs. In sum, insomniacs show smaller reductions in brain arousal from wake to sleep (which explains their difficulty sleeping) and less brain arousal during the morning (which explains their fatigue).