We intuitively know that sleep is important for our health and wellbeing. Probably all of us have experienced the negative consequences of its shortage, such as impaired concentration, slower reaction times or inability to engage in more strenuous activities. It’s estimated that over a quarter of Poles suffer from a chronic shortage of sleep. It has also turned out that sleep deficiency has a negative impact on the periods of rest.

How does chronic sleep deficiency influence neurological activity? How to conduct research aimed at answering this question? Dr Jeremi Ochab from the Department of Theory of Complex Systems at the JU Institute of Physics explains how analytical methods used in statistical physics are applied in neuropsychology.

Wrist activity – the key indicator

The joint study by researchers from the JU Institute of Physics and the JU Institute of Applied Psychology was based on the use of a special bracelet, known as an actigraph, which measures the power and frequency of wrist movements in the non-dominant hand. Several dozen people agreed to wear this device, which registered their activity during the several following days and nights, when their regenerative needs were fully met. As a result, the activity of each participant was illustrated as a graph. Having obtained these data, the researchers asked the subjects to reduce their sleep time by 30 percent during the following ten days and then compared the results registered by the actigraphs. “Generally speaking, side effects were identified in all participants after three or four days of the second stage of research”, says Dr Jeremi Ochab. The symptoms included decrease in mood, limited control over falling asleep during the day, and feeling cold. After ten days, the subjects were once again allowed to sleep as long as they wanted. The researchers wanted to know if and how the participants were able to recover from sleep shortage symptoms.

Lack of sleep = lack of effectiveness

The actigraph data from the period of shorter sleep have clearly shown that while it was difficult to identify any significant differences in measurements during active phases, the frequency and force of the participants’ wrist movements when they were inactive (for instance, watched TV) changed in a way suggesting that the shortage of sleep led to more frequent rest interruptions. For example, during a period of 10-minute rest, 9 out of 10 wrist movements of people who’ve had enough sleep occurred in the last minute of this period, whereas persons who lacked sleep made one such movement per minute during the same time period. Hence, the quality of their rest was significantly lower, as it is divided into ten separate parts.

The study also involved EEG measurements, which registered the electrical activity of the brain. During the 21-day study, the subjects’ brain activity was recorded each day during performing a mental task and during rest. The persons who suffered from effects of sleep shortage performed the task less effectively. In addition, the resultant reduction of neuronal activity lasted after the participants returned to their normal pattern of sleep and wakefulness.

It was also observed that after a half-minute break during the task, the subjects reacted to stimuli more quickly, which, as pointed out by Dr Ochab, illustrates the importance of taking breaks during work requiring high concentration levels.

What are the practical implications of these results? First of all, it should be ensured that people whose jobs require maintaining high concentration levels, such airplane pilots, get enough sleep, not only for the sake of effectiveness of their work, but, most importantly, the safety of other people.

As the pace of life has speeded up, sleep deficiency has become a common phenomenon, which brings us to another question: is it possible to compensate it with better satisfaction of other physiological needs? “It seems that the only effective way to adapt to constant sleep shortages is to die”, jokes Dr Ochab. This seems to be confirmed by other studies, which indicated that after only a week of severe reduction of sleep, the susceptibility to viral infections increases threefold.

An effective diagnostic tool

Actigraph records can also be used for other purposes than studying the effects of sleep deficit, for instance, as an additional tool in the diagnosis of neuropsychiatric disorders, such as the Parkinson’s disease, Alzheimer’s or depression. Researchers from the two aforementioned JU institutes as well as the JU Institute of Applied Psychology have used actigraphic data to effectively diagnose attention-deficit hyperactivity disorder (ADHD) and Asperger syndrome in children aged 9-11, indicating that the method can be used as an independent diagnostic tool¹.

Using actigraphy supported by machine learning to spot abnormal behaviour patterns turns out to a very promising method to conduct large-scale neuropsychological studies. The scientists hope that in near future it can be used to effectively help people suffering from circadian rhythm sleep disorders.

 ¹ H. Armitage, Lack of sleep puts you at higher risk for colds, first experimental study finds, in: "Science", Sept. 2015.

Original text: www.nauka.uj.edu.pl