Sleep deprivation is simply the condition of not having enough sleep. Beyond this, it can cause fatigue, daytime sleepiness, clumsiness and weight loss or weight gain. In addition, sleep deprivation may be linked to serious diseases, such as heart disease and mental illness including psychosis and bipolar disorder. Most importantly, sleep deprivation adversely affects the brain and cognitive function.
Earlier studies, using functional magnetic resonance imaging, have shown brain’s prefrontal cortex (the area that supports mental faculties such as working memory and logical and practical reasoning) display more activity in sleepier subjects. This means, in those who don’t get sufficient sleep, the brain has to keep on working harder.
A new study from the University of Surrey (U.K.) has shown more variation with different regions of the brain in relation to sleep deprivation than previous research has identified. For example, brain regions associated with problem solving and concentration become noticeably sluggish when sleep-deprived. However, other areas are less affected by sleep debt. The different observations have helped advance this area of neurobiology.
There are two factors that affect how the human body responds to sleep (or the lack of it). The first is the 24-hour circadian clock and the second is body’s drive to sleep, which becomes greater the longer a person is awake.
All animals and plants have a built-in circadian rhythm, which is adjusted to the environment by external cues such as daylight. The human brain’s internal circadian clock is centered in the hypothalamus region of the basal forebrain. Correct functioning of the internal clock is important for the internal clock regulates sleeping and feeding patterns, body temperature, brain wave activity, hormone production, regulation of glucose and insulin levels, and a range of other biological activities.
With the new study, researchers assessed the cognitive function of 33 adults who were asked to go without sleep, under laboratory conditions, for 42 hours. Over the duration of this sleepless period, the participants were requested to perform some simple tasks designed to examine reaction time and memory. The subjects also underwent 12 brain scans across the 42 hours and another scan after they’d experienced a welcomed 12 hours of recovery sleep. As well as brain activity the researchers also assessed levels of the sleep hormone melatonin.
The study found activity in some brain areas, like the thalamus, varied in synchronicity with the circadian clock. However, with other areas like the brain’s outer layer, the activity was completely out of line with the natural body clock.
Unsurprisingly, sleep deprivation affected the participants’ ability to carry out simple tasks. Although it was of interest that performance with the test was weaker at night and then improved during the second day.
Interviewed by Science News, the lead author of the new research, Dr. Derk-Jan Dijk said: “We’ve shown what shift workers already know. Being awake at 6 a.m. after a night of no sleep, it isn’t easy. But what wasn’t known was the remarkably different response of these brain areas.”
The results of the new study are of interest not only in relation the lack of sleep, they may also offer insights into neurodegenerative diseases like Alzheimer’s disease. This is because some forms of dementia are not consistently manifested. Some people with dementia exhibit worsening symptoms as the day progresses, indicating that tiredness makes dementia worse.
The new research has been published in the journal Science. The research paper is titled ” Local modulation of human brain responses by circadian rhythmicity and sleep debt.”
This article is part of Digital Journal’s regular Essential Science columns. Each week we explore a topical and important scientific issue. Last week we looked at how spider webs are inspiring research into next generation electronics. The week before we examined a new warning about cancer risks relating to drinking alcohol.
