Vulnerability to Sleep Loss Varies by Individual
Researchers studying the effects of sleep restriction on brain function have found that some individuals are more vulnerable to sleep deprivation than others, and that the ability to recover from chronic sleep restriction also varies.
Through a series of nine studies, David Dinges, PhD, Professor and Chief of the Division of Sleep and Chronobiology in the Department of Psychiatry at the University of Pennsylvania School of Medicine in Philadelphia, and colleagues sought to identify changes in brain function as a result of chronic sleep deprivation, as well as differences in individuals’ sleep need, vulnerability to sleep restrictions, and ease of recovery after sleep deprivation.
The studies involved more than 500 healthy adults, including men, women, whites, and minorities. The average age of participants was 30 (range, 21 to 50). Each study included 40 to 150 participants, who lived in the laboratory 24 hours a day for two to three weeks.
The researchers found that there were large individual differences among healthy persons in response to chronic sleep restriction. Some people were severely affected and showed a dramatic decline in alertness from continued deprivation. Others were not as severely affected, and a subset showed no cognitive deficits from the sleep restriction.
“Our findings indicate that there are likely people who are resistant to the effects of sleep restriction and those who are very vulnerable,” said Dr. Dinges. “Even though they all obtain the same amount of sleep normally in their lives, and even though they are getting the same restriction in the laboratory, they are having markedly different neurobehavioral responses to the reduction of sleep.”
The researchers found that all subjects who slept seven to eight hours a night functioned normally, but with each day of sleep restriction, differences between the groups started to emerge. As sleep was reduced, cognitive functioning was impaired, with the rate of change determined by membership in one of the three groups. Changes began to occur when participants slept fewer than seven hours each night and became much more dramatic when sleep time was reduced to four hours per night.
Through psychomotor vigilance testing, a test of sustained attention that is used to detect sleepiness, the investigators identified the effects of sleep restriction on each participant. Using this test as a marker, they found that attention was profoundly affected by inadequate sleep. For most people, attention destabilizes early in the sleep restriction and was more affected by restriction than any other cognitive area. However, not everyone showed these effects.
“This is not a simple story, because each person’s sleep needs and response to sleep restriction are unique,” Dr. Dinges said. “The bottom line is that it is important not to restrict your sleep, and that if you do it night after night, most people will begin to see the effects in behavior and brain function. Furthermore, it’s important to oversleep when possible in order to recover from any sleep deficit to the extent possible.”
High-Fat Diet During Pregnancy Causes Brain Inflammation in Offspring
A pregnant mother’s high-fat diet can have profound and lasting effects on the brain of her offspring, according to evidence from an animal study. Researchers believe that high-fat diets activate immune cells in the brain, causing inflammation, a process that may lead to neurodegenerative conditions such as multiple sclerosis and Alzheimer’s disease.
“Obesity is generally thought of as a condition that happens to the body but doesn’t impact the brain,” said Staci Bilbo, PhD, Assistant Professor of Psychology and Neuroscience at Duke University in Durham, North Carolina. “But our research found that changes in the brain of offspring are linked to what a mother eats during pregnancy.”
Previous research has shown a link between obesity and inflammation in the body, but little is known about whether obesity might affect inflammation in the brain or if obesity in a pregnant mother can affect brain functions in her offspring. Dr. Bilbo and her team investigated how immune cells in the brain of a pup respond to or are activated by a high-fat content in its mother’s diet during pregnancy.
“When the brain’s immune system is out of balance, it becomes inflamed,” said Dr. Bilbo. “Inflammation is good in the short term, because it can aid in healing and alert us to tissue damage, but in the long run, constant inflammation can be damaging to neurons and brain function.”
The researchers fed female breeding rats one of three diets—a 60% saturated high-fat diet, a 60% trans high-fat diet, or a 10% low-fat control diet for four weeks prior to mating and throughout pregnancy and lactation. After weaning (day 21), all pups were fed the low-fat diet, so they were never on a high-fat diet themselves.