The Clinical Neuroscience of Sleep and Insomnia

Recent developments in neuroscience suggest that sleep disorders, such as insomnia, are tied to the dysregulation of the sleep-wake switching system. This research was discussed here at the annual meeting of the American Psychiatric Association (APA).

Input from the prefrontal cortex and limbic system can in turn influence the occurrence and emotional tone associated with sleep and wakefulness. "There is a biological timing system that influences the overall tone and timing of sleep and awakeness," said Daniel J. Buysse, MD, Professor of Psychiatry, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States. "You cannot just will yourself to sleep."

Buysse presented the case of a 40-year-old woman, "Kathy," who had just lost her teaching job and who was going through a divorce and custody battle over her two children. She complained of difficulty falling asleep and staying asleep. As a consequence, she said, she had cognitive difficulties, problems concentrating and focusing, feelings of fatigue, and lack of energy. She would have a few bad nights generally followed by a few good nights' sleep, but sleep was always worse after experiencing upsetting events. A sleep evaluation found that she had a long-term tendency toward sleep problems and had tried various over-the-counter methods to get desired sleep.

Buysse asked the audience of psychiatrists which aspect of Kathy's presentation was most likely related to a decreased homeostatic sleep drive. Thirty-nine percent thought she was possibly napping during the day and ruining her chance of a full night's sleep.

"Daytime symptoms associated with insomnia, all seen in Kathy's case," Buysse said, "fall into three areas: mood disturbance, cognitive difficulties, and difficulty focusing with fatigue."

While a sleep lab may show that a person is sleeping, people with insomnia conversely feel they are simultaneously awakened during sleep. "To their brain, it's day," he said, explaining the implications of the sleep-wake switching system for insomnia." Buysse said to tell patients with insomnia not to sleep during the day "because if you nap during the day, you're not going to have enough sleep drive to get to sleep at night." It was also suggested that patients get up at the same time every day so they receive enough light as the circadian system requires it.

There can be lesions of perifornical orexin (another name for hypocretin, a chemical secreted in the hypothalamus that regulates the sleep-wake cycle) neurons that produce unstable sleep-wake states with frequent wake-sleep transitions.

In rat studies, when their cages are swapped out, the rats have reduced sleep due to stress. This stress-induced insomnia may produce a "flickering" of the sleep-wake switch. There are actually simultaneous sleep and wake centres on at the same time when the rat is stressed. In human populations, however, asking someone how they sleep may be better than objective tests since the flickering tests cannot be accomplished with a routine psychiatric practice, Buysse said.