The Yomiuri Shimbun
People who lack sleep tend to be more anxious and irritated than their well-rested counterparts because the brain becomes more sensitive to unpleasant things when we are tired, a group of researchers at the National Center of Neurology and Psychiatry has found.
The group was led by Dr. Kazuo Mishima, chief of the center's Department of Psychophysiology.
The team asked 14 men aged between 20 and 31 to take a four-hour sleep for five consecutive days, then an eight-hour sleep for five days, and monitored their brain activity on the final days of each period using functional magnetic resonance imaging (fMRI).
When the four-hour sleep group looked at images of faces expressing fear, their amygdala--part of the brain thought to play a primary role in processing emotions--became more active compared to the eight-hour group. No difference was seen when they saw pictures of happy faces.
The research also found that participants whose amygdala became more active due to a lack of sleep tended to show more signs of anxiety, irritability and confusion on psychological tests.
Japanese sleep an average of seven hours and 50 minutes a day, the second-lowest among developed countries following South Korea.
"There is serious sleep shortage among the working population, especially among women," Mishima said. "It is important to get a sufficient amount of sleep to stay mentally fit."
(Jul. 2, 2012)
http://www.yomiuri.co.jp/dy/national/T120701002329.htm