Brain structure linked to insomnia and REM latency
The pineal gland, a small pine cone shaped endocrine gland located in the brain, plays an important role in the regulation of the sleep-wake cycle through its release of melatonin. Preliminary evidence indicates that pineal gland volume (PGV) is related to melatonin secretion; and melatonin secretion has been associated with disturbances of the sleep-wake cycle. Drawing on evidence that melatonin levels have been shown to be altered in small studies of insomnia patients, the authors of a recent article published online in the Journal of Sleep Research sought to investigate whether PGV may differ in patients with primary insomnia relative to healthy good sleepers.
The research team recruited 23 untreated patients with insomnia and 27 matched healthy good sleepers. All participants stayed for 2 nights in the sleep laboratory, helping to rule out additional sleep disorders and providing a baseline assessment of sleep. Participants were then scanned using a 3-Tesla Magnetic Resonance scanner and pineal borders on the scans were defined manually by an experienced neuroradiologist (blind to group).
The main findings indicated that PGV was significantly smaller in patients (mean = 48.9 mm3) relative to controls (mean=79.0 mm3). Exploratory analysis, investigating associations between PGV and sleep recorded in the laboratory, revealed a positive correlation between pineal gland size and REM latency. Those with smaller pineal gland volumes tended to have a reduced latency to REM sleep, a possible marker of sleep dysfunction that may be mediated by altered melatonin levels.
This is the first report to show differences in PGV in insomnia, potentially (re)igniting interest in the circadian processes that may play a role in the etiology of poor sleep. As the authors note, however, the direction of the relationship requires scrutiny in further studies.
Bumb, J.M., Schilling, C., Enning, F., Haddad, L., Paul, F., Lederbogen, F., Deuschle, M., Schredl, M., Nolte, I. (2014). Pineal gland volume in primary insomnia and healthy controls: a magnetic resonance imaging study. Journal of Sleep Research. doi: 10.1111/jsr.12125