The Effects of Sleep Deprivation: Exploring Cognitive Performance

Introduction 

Not only has poor sleep been shown to have physical health implications, but research has shown sleep is vital for maximum cognitive performance. Studies have shown too little or too much sleep can be detrimental to cognitive functions such as attention, thinking, and memory, and demonstrated cognitive deficits can become severe over time. Studying the effects of altered sleep patterns on cognitive performance has practical applications, for example in shift work. Cognitive impairment is thought to lead to a decline in efficiency in the workplace, which in a clinical environment, could put healthcare workers and patients at risk, therefore effective strategies are needed. This 'Effects of sleep deprivation' essay will examine evidence to critically evaluate claims that altered sleep patterns affect cognitive performance.

Effects of sleep deprivation

Many studies have looked at how sleep can affect cognitive performance. Pilcher et al., 2010 found that sleep-deprived participants performed significantly worse on complex cognitive tasks than controls. Similarly, Horne, 1988 found sleep-deprived participants had worse creativity, showing poorer flexibility and originality in tasks. Wimmer et al., 1992 replicated these findings, showing sleep loss resulted in decreased cognitive abilities. These studies can all be criticized on their small samples, of just 12 (Wimmer et al., 1992 and Horne, 1988) and 44 (Pilcher et al., 2010). Both Wimmer et al., 1992 and Pilcher et al., 2010 used students, so findings may not be generalizable to different educational backgrounds or ages. Despite these limitations, these studies assessed participant responses to a range of cognitive tasks and contributed to knowledge regarding the effects of sleep deprivation on cognitive performance. Prior to Horne, 1988, the effects of sleep loss on divergent thinking had received little attention so this provided useful information. These studies have practical applications, for example, Pilcher et al., 2010 showed college students may be sabotaging their performance by not sleeping enough and may encourage them to think carefully about this.

Although the functions of sleep remain largely unknown, substantial evidence suggests sleep is essential for memory formation. Drummond et al., 2000, studied the effects of sleep deprivation on the encoding of a verbal memory task and found significantly worse acquisition of verbal learning in sleep-deprived participants. Similarly, Harrison-Horne, 2000, found sleep deprivation impaired temporal memory. These studies can be criticized on their small samples of 13 (Drummond et al, 2000) and 40 (Harrison-Horne et al., 2000). Drummond et al., 2000 can be criticized as the study took place in the early evening when participants were near the Wake Maintenance Zone (WMZ) when cognitive performance is near its peak (Monk et al., 1997). Had the study taken place in the morning, more errors may have occurred and this needs to be studied. Despite these limitations, both studies were well-controlled. Drummond et al., 2000, used FMRI, allowing researchers to measure non-conscious brain processes. Harrison-Horne et al., 2000, used an actimeter to monitor sleep prior to testing, to ensure participants obtained their usual amounts. They also considered the effects of delay between tasks, by occupying participants. Drummond et al., 2000, contributed valuable knowledge to this area as prior to this, only three studies had examined the effects of sleep deprivation on cerebral functioning and behavioral performance.

Sleep has also been shown to affect learning. Tamaki et al., 2020, found participants performed better on a visual learning task when allowed a 90-minute nap after the task, prior to being tested again. Participants that had more NREM sleep performed better, as during NREM there is an increase in glutamate, which allows the brain to form new connections and enhances learning. The study can be criticized as it doesn’t inform us about what happens in the brain over a full night’s sleep. However, a Magnetic resonance spectroscopy machine (MRS) was used to measure brain processes and it is unlikely anyone would be willing to spend a full night in an MRS machine, so this is difficult to measure. Despite these criticisms, the use of scientific methods allowed researchers to measure brain changes during sleep and how these affect learning, which could allow for further study with potential practical application. For example, whether it is possible to increase GABA production in sleep to aid learning, e.g. using medication.

It is not just sleep deprivation that can be an issue. Research has shown too much sleep is also linked to worse cognition (Devore et al., 2014). This study only included female nurses aged 70 with similar educational backgrounds, so may not be generalizable to men or younger generations. Despite these criticisms, the study can be praised for its huge sample of 15,385 participants, which meant a huge amount of data was collected. The study consisted of four repeated assessments over 6 years, so researchers assessed participants’ changes over time.

Shift work can also be problematic. Deepalakshmi Kaliyaperumal et al., 2017 found impaired cognitive performance among shift-working nurses, due to poor sleep quality and decreased alertness. However, as nurses are predominantly female, 97% of the participants were female, so findings may not be generalizable to men. A strength of the study was that participants had previous work experience of at least one year in rotating shift work, so results provide information about the long-term effects of shift work. Also, participants varied in ethnicity and age (from 20-50), so findings are generalizable.

Conclusion

In conclusion, the overwhelming balance of evidence suggests that altered sleep patterns can affect cognitive performance, particularly memory processing, learning, thinking, and attention. Despite the limitations of studies, mainly related to methodology, the consistency across trials means we can be confident in our findings. Studies have practical applications, for example in helping us understand and address the risks of shift work. However, a key criticism of studies is that most assess participants using arbitrary tasks and include participants who would not normally experience sleep deprivation or disturbed sleep. Therefore, more studies using highly scientific methods need to be conducted, ideally using shift workers, military personnel, etc. to gain more information on the long-term effects of sleep deprivation and assess the idea that the brain could potentially adapt to these conditions.