I’m getting ready to give a talk on stress-related insomnia and I’ve come across a fascinating study published five years ago. Neuroscientists at Harvard used rats to uncover a novel insight about what may be going on in the human brain when stress interferes with our sleep, and a better way to calm the brain down.
To introduce psychological stress—the type of stress that often underlies insomnia—in their rodent subjects, the investigators placed half of the rats in dirty cages previously occupied by a male competitor. (The other rats, placed in clean cages, were used as controls.) The smell of the rival rat—even though that rat was no longer present—and the inability to escape from the rival rat’s territory created a normal stress response in the cage exchange rats. Their temperature went up, and there was a big increase in neural activity in the brain. Clearly these rats were stressed out.
But it was not the initial stress response that the researchers wanted to study. They wanted to study what happened when the acute stress had subsided, when the rats finished exploring their new surroundings and finally went to sleep.
The control rats slept normally. But cage exchange rats took longer to fall asleep, woke up more frequently during the sleep period, and slept about 25 percent less than the control rats. All this was expected.
The Big Revelation
The news came when investigators looked at what was going on inside the rats’ brains.
Previously, scientists had assumed that sleep and wake-time were whole-brain states. Either the arousal system was in control (completely inhibiting the sleep system) or the sleep system was in control (completely inhibiting the wake system). There were no halfway states.
But analyzing the neural activity in the brains of the cage-exchange rats, the Harvard researchers did find evidence of what they call “an intermediate state.” What did it look like?
The sleep-promoting areas of the brain were fully active, reflecting strong sleep drive and clear evidence that parts of the brain were deeply asleep. At the same time, neurons in key areas of the brain active during wakefulness were firing away like crazy. Areas associated with fear, anxiety, and emotional processing were behaving as if the rats were wide awake.
“These results suggest that both sleep-promoting areas and part of the arousal system are most likely simultaneously activated during the period of stress-induced sleep disturbances,” the scientists said.
A Better Kind of Sleeping Pill
How did investigators get the sleep of cage-exchange rats to look normal? Not by enhancing activity of the sleep system—that system was already fully engaged. They enabled normal sleep by blocking activity in the areas of stress-induced arousal.
Most sleeping pills on the market today put us to sleep by enhancing activity of the sleep system. But the rat study, say these Harvard scientists, suggests that a more appropriate target for sleep medications would be tamping down activity in the arousal and emotion centers of the brain.
Does stress interfere with your sleep? How do you deal with it?