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Cognition And Sleep: The Influences Of Bad Sleep On Cognition

Cognition And Sleep: The Influences Of Bad Sleep On Cognition

Medicine is well aware of the harmful effects that poor quality nights of sleep have on our health. But scientists still don’t know very well how this affects our cognitionour memory and our ability to concentrate. The truth is that we need to sleep an average of 8 hours a day – apart from short and long sleepers – which means that we spend a third of our lives sleeping. Therefore, quality sleep is as important to our health as eating well and practicing regular physical activity.

Today’s post was prepared by our experts in order to address the relation between cognition and sleep and the influences that bad sleep has on cognition. What are the consequences of poor sleep on our cognition? Did you know that research has linked irregular nights of sleep to the effects of alcohol on the brain? Get to know more about the influences that bad sleep has on cognition below.

What cognition is

From the Latin congnoscere, which means to know, cognition is everything that is related to knowledge. Cognition is the ability we have to process information through perception, assimilating and processing information that we obtain from the most diverse sources, such as our perceptions, experiences, beliefs, readings, conversations, and so on.

According to the Michaelis dictionary definition, cognition is “the act or effect of knowing; knowledge acquisition process; knowledge; a set of conscious mental processes that are based on sensory experiences, thoughts, representations and memories”.

Cognition consists of several cognitive processes, including learning, attention, memory, language, reasoning, and decision-making, which help us to develop intellectually. Cognition is widely studied in neurology, psychology, anthropology, and even philosophy. But it is cognitive psychology, which emerged in the late 1950s, that studies and analyzes it more deeply, evaluating how the information process will influence our behavior and what is the relationship between different mental processes and knowledge.

Interest in cognition grew a lot from the 1960s onwards, and authors such as biologist Jean Piaget and psychologist Lev Semionovich Vigotsky contributed greatly to its understanding. Advances in the field of neuroimaging bring deeper psychological and neuroanatomical knowledge, allowing science to better understand mental processes and their influence on our behaviors and emotions.

What are sleep disorders?

In order to talk and understand a little more about cognition and the influences that poor quality, non-restorative and insufficient sleep can have on it, it is also important to talk about sleep disorders. In short, sleep disorders are diseases that directly affect the quality of sleep on a regular basis.

The best known sleep disorders are insomnia, sleep apnea, night terror, narcolepsy, sleepwalking, restless legs syndrome and bruxism, among others. These sleep disorders rob us of quality of life, cause tiredness, irritation, mood swings, drowsiness throughout the day, difficulty concentrating, drop in performance and headaches. They can also cause even more serious consequences such as depression, stroke or even cardiovascular disease.

Sleep disturbances, a consequence of regular sleepless nights, directly affect our cognition, and that’s what we’ll be addressing below.

Sleep vs. Brain Functioning

How can sleep quality influence the functioning of our brain? Scientists from the Psychiatry and Neuropsychiatric departments of South Korea decided to seek an answer to this question through the study “Sleep and Cognitive Decline: A Prospective Non-demented Elderly Cohort Study”, published in 2018 in the Annals of Neurology, a renowned medical journal dedicated to publishing and disseminating scientific articles focused on neurology. The main objective of the researchers was to deepen the knowledge and understanding of the relationship between sleep quality and the development of cognitive impairment in the elderly.

Over a four-year period, sleep quality and its changes in cognitive function in 2,893 people aged 60 years and over with normal cognition (NC) or mild cognitive decline (MCL) were individually assessed. Average sleep time, age, gender, education, depression, cumulative disease scale (CIRS), socioeconomic status, work, smoking, physical activity, sleep disorders and sleep apnea assessment were evaluated.

Results and conclusion

The results of research participants with normal cognition (NC) showed that individuals with long sleep duration, who take longer to sleep or have the half sleep phase (the time that half of the total sleep duration occurs) at later hours are associated with a higher prevalence of cognitive decline when compared to subjects with healthier sleep.

Among the participants who present cognitive decline, it was observed that individuals who take longer to sleep (long sleep alertness) have 30% less chance of reversing the cognitive deficit picture when compared to individuals with short sleep latency and half-stage baseline sleep were not associated with cognitive changes.

The researchers also found that long sleep latency in the group with cognitive impairment did not affect the incidence of dementia, which made them believe that this is possibly not a risk factor, but rather an early sign of onset of dementia in patients. Among participants with normal cognition, long sleep duration increased the risk of incidence of cognitive decline by 1.7 times.

The scientists’ conclusion was:

• Long sleep latency can be used as an early marker of cognitive decline for elderly people with normal cognition and cognitive deficit. 

• Increased sleep duration and late half-sleep phase can be used as markers only for elderly people with normal cognition.

Remember that not only sleep duration should be taken into account for a restorative night’s sleep. Sleep quality should also be taken into consideration. An individual with a long duration of poor sleep may have worse sleep than an individual with a short duration of good quality sleep. To understand more about these aspects, it is recommended to follow the sleep routine through actigraphy.

The consequence of lack of sleep on the brain

To demonstrate the effect of lack of sleep on our brain, the Brain and Mind Institute at Western University in Canada is carrying out extensive research, coordinated by British neuroscientist Adrian Owen, on the effect of lack of sleep on the brain with thousands of volunteers from all over the world. Scientists believe they will be able to determine an average number of hours needed to optimize brain function, although the need for sleep is absolutely individual.

A quick experiment was done with five volunteers, who spent a night at the university: a 42-year-old psychiatrist, used to night shifts, a 31-year-old mother of two little girls, a 75-year-old retired security guard, a 31-year-old neuroscientist, who does cognitive research with mice, which requires him to work at night, and a BBC journalist. During the experiment, they performed four tests on computers, tablets and smartphones.

The group stayed awake until 4:00 AM, and were then able to sleep for four hours, when the tests were re-run in the morning. The journalist, the retired security guard and the neuroscientist performed much worse than observed the night before. The psychiatrist’s performance barely changed, but that of the girls’ mother did improve. She said she was very used to waking up and immediately being needed by her daughters.

The researchers performed a CT scan of the journalist’s brain as he repeated the tests. His brain was examined twice, after a normal night’s sleep and after a bad night’s sleep. Comparing the images showed that lack of sleep resulted in very low brain activity, with less activity in the frontal and parietal lobes, which are key areas of our brain for decision-making, problem-solving and linked to memory.

In another study in which the sleep duration of the participants was controlled, it was observed that after 14 days of sleep restriction, individuals who slept 6 hours or less had cognitive deficits similar to those of individuals who spent 24 hours without sleep, which could reach to a cognitive deficit similar to that of subjects who spent 3 days in total sleep deprivation!

How does sleep help the brain to reorganize itself?

Research published in the prestigious scientific journal Nature Communications shows that regular and quality sleep has a positive effect and helps our brain to organize itself, which is fundamental for our cognition. According to the research, resting the brain, through a good night’s sleep, allows a positive impact on memory and on learning in everyday life.

According to the research, the activity in the dendrites (a specific region of neurons) is intensified, and this structure is fundamental for the nervous system’s capacity to change and meet new demands. Research has shown that the increase in performance of so-called dendrites is closely linked to “spindles”, brain waves emitted when we sleep, which influence the formation of memories.

“Sleep spindles were associated with memory formation in human beings for some time, but no one knew what they were actually doing in the brain. We now know that during spindles, specific pathways are activated in dendrites, perhaps allowing our memories to be reinforced during sleep. Our brains are amazing and fascinating organs, they have the ability to change and adapt based on our experiences. It is increasingly clear that sleep plays an important role in these adaptive changes and our study shows that a large proportion of these changes can occur during time zones”, said study leader, researcher Julie Seibt, from the University of Survey.

Scientists used laboratory rats to measure calcium ion levels in dendrites and measured the frequency of the “spindles” using an electroencephalogram. Thus, they could observe that the increase in electrical flux in the dendrites coincides with a greater occurrence of “spindles”. That’s when the brain’s reorganization process happens, which proves the good effects of a good night’s sleep for our cognition.

Bad sleep: impact on the brain is the same as that caused by alcohol

An important and revealing study entitled “Selective neuronal lapses precede human cognitive lapses following sleep deprivation”, published in the respected scientific journal Nature, reveals that sleepless nights can result in memory lapses and a distorted visual perception due to a temporary communication failure between neurons. According to the researchers who led this study, the effects can be similar to drunkenness.

The study was conducted by researchers at the University of Los Angeles, USA, and Tel Aviv University, Israel, with 12 volunteers with epilepsy. Electrodes were implanted in their brains to record how often seizures happened and where they originated. It was decided to induce seizures through sleep deprivation, that is, participants had to stay awake at night until they had a seizure episode, and they needed to perform small cognitive tasks, such as sorting images into categories as quickly as possible.

Scientists evaluated the brain activity of the temporal lobe, associated with memory and visual recognition. The more tired and sleepy, the more difficult it was for the participants to perform the tasks. According to researchers, lack of sleep reduces the ability of our neurons to function, which can cause lapses in our cognition. Sleep deprivation, the research found, affects how neurons encode information and how visual stimuli are read, something very similar to the consequences of alcohol consumption.

This group of researchers is expanding the study, now dedicating themselves to understanding the brain mechanisms responsible for memory and perception lapses and the benefits that a good night’s sleep brings.

Sleep disorders and actigraphy

Obviously, we all eventually get a bad night’s sleep, and we know well that the next day is more difficult because of that. But when this happens regularly, it is necessary to investigate its causes, since the person is probably suffering from a sleep disorder. The main cause of irregular night’s sleep is some kind of sleep disorder.

An important and revealing test that can be requested by the doctor for those who have some type of sleep disorder is actigraphy. Through the actigraph, which most often resembles a wristwatch, it is possible to follow the cycles of activity and rest, alongside the capture, compilation and processing of information to study the rhythm of sleep and wakefulness and the consequences of disorders of circadian rhythm.

More modern actigraphs have temperature and light sensors, allowing for greater depth of data analysis. This is a test much requested by doctors, especially sleep doctors, which can help to identify the diagnosis and, thus, point out the treatment to be done.


You don’t need to be a scientist, doctor or psychologist to realize how bad a night’s sleep (or sleep deprivation) makes us sick. But the repetition of this condition can affect our health in a drastic way. It is not yet known exactly why an irregular night’s sleep affects our cognition, but research has identified this direct relation between cognition and sleep.

The truth is, a restful night’s sleep is critical to our health, just as it’s absolutely important to eat well and exercise regularly – every doctor will agree with that, no exceptions. The most varied neurobiological processes that take place during sleep are essential for the maintenance of our physical and cognitive health, including emotion and memory. Studies linking cognition and sleep, as well as the influences that bad sleep has on cognition, show that people deprived of sleep have a significant worsening of cognitive activities, which means a lower performance capacity.


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