|Symptoms of Sleep deprivation|
|A list of the main effects the lack of sleep can have on ones body.|
Sleep is a natural repetitive loss of consciousness that is reversible and occurs in all organisms that contain a complex nervous system. In a world that has become fast paced and demanding on productivity, sleep has become a waste of valuable time. However, the deprivation of sleep, either acute or chronic has been shown to cause adverse effects on one's higher-level cognitive capacities, attention, memory and mood. Those suffering from the lack of sleep also show elevations in clinical scales measuring many mental health disorders. Though there is a large quantity of information on the effects of sleep deprivation, little is actually known about the mechanism that causes such symptoms.
1 The effects of insufficient sleep on the human body
1.1 Attention and Vigilance
|Psychomotor Vigilance test|
|Astronaut Richard Arnold, performs the Psychomotor Vigilance Test (PVT) Self Test.|
Ones ability to stay attentive for a period of time and to be able to respond to some form of stimulus is greatly impacted by sleep deprivation. Scientists can test ones alertness and vigilance, through a person’s reaction time and their accuracy in a psychomotor vigilance test. The psychomotor vigilance test is a simple 10-minuet long reaction time test that randomly presents a person with a visual cue within a period of 2 to 10 seconds. The person then has to press a button as quickly as possible. However, should it take longer than 500 milliseconds to respond to the cue, this means that the person had an attention lapse, which is thought to be the brain entering a form of microsleep.
With the use of these methods, scientists have found quantitative results of how much sleep deprivation effects our alertness and vigilance. In one experiment, it was found that one’s reaction time and accuracy begins to be impair a person after 16 hours of wakefulness. Also, this experiment showed that the longer wakefulness was prolonged, the more significant the slowing of reaction time, and the more increased amount and duration of attention lapses that occurred. Surprisingly, there was also the occurrence of false alarms, where the person would press the button when there was no visual cue. These false alarms increased with the amount of time the person was kept awake. Lastly, the ability for one to sustain their psychomotor vigilance decreased with the increased duration of psychomotor test. This time-on-task-effect means that one's ability to stay focus depended on the length of the psychomotor test. The longer the testing period is extended, the less attentive the person becomes thus a worsening of response time results.
Another experiment investigated if attention and vigilance are affected by the restriction in the amount of sleep one receives per night. It was shown that a person restricted to 6 hours of sleep per night for two weeks showed results comparable to a person who was sleep deprived for two nights. The same results are shown for a person who was restricted to 5 or 4 hours a night. However if a person was restricted to less then 4 hours a night, their psychomotor test results degrade much more rapidly. Thus in conclusion attention and vigilance is effected by sleep deprivation.
1.2 Effects on processing of Sensory Information
Little has been studied about how our mind integrates sensory information when sleep deprived. In the case of taste, a very early study suggested that sleep deprivation caused an increased sensory threshold for sour tastes but not for sweet and salty. However, it is believed that the reduced sensitivity was caused by the decrease of attention from the individuals due to the 48 hours of sleep deprivation. One’s tactile perception and pain is also influenced by sleep deprivation through an increase of sensitivity. When one is sleep deprived they have a lower pain tolerance for cold and heat. Sleep deprivation is also associated with a significant increase of spontaneous pain, such as discomfort, body pain, headache, muscle pain, and stomach pain.
|Pain from sleep deprivation|
|A young man who stayed up for 72 hours. He speaks a bit about the pain he is feeling.|
Another sensory perception that has been studied is auditory perception. Sleep deprivation affects the auditory temporal resolution, which is the ability of an individual to distinguish 2 close paired auditory stimulus and determine which occurred first. This ability is processed in the pre-frontal cortex, which is an area particularly sensitive to sleep deprivation. It has also been shown that one night of sleep deprivation will reduce auditory temporal resolution by over 28%. Lastly, the olfactory perception is integrated in the orbitofrontal cortex, which is one of the areas partially affected by sleep deprivation. Two experiments have been conducted recently for olfactory perception and both used a smell identification test (SIT), which is a standardized measure of olfactory discrimination. The first test used individuals who had been sleep deprived for 24 hours while the second experiment used individuals who had been sleep deprived for 52 hours. However, while both showed that there was a decline is olfactory perception, it was only a mild decrease of about 5.2% to 6.3% on average.
1.3 Emotional Perception and Mood
People who are sleep deprived are commonly known to be very unpleasant. They are easily frustrated, irritable, intolerant, unforgiving, indifferent, and more self-focused than usual. They also seem to carry an aura of melancholy. Even a single night without sleep leads to the person having a significant negative rated mood scores. In one experiment, scientists interviewed people who where suffering from sleep deprivation and questioned them on their feelings. Many people reported negative moods of worthlessness, inadequacy, powerlessness, failure, low self esteem and reduced life satisfaction. A similar report instead measured one’s disposition through the use of clinical scales. They found that people who were suffering from sleep deprived for 56 hours reported significant elevation in clinical scales measuring depression, anxiety, paranoia and somatic complaints. Overall, ones mood is negatively effected by sleep deprivation.
The negative temperament that people contain when lacking sleep also effects their perception of the environment around them. People appear to approach events much more jaded and negatively. In one experiment to test ones perception, the researchers used three types of themed photos (negative, neutral and positive) and ask the sleep-deprived individual to rate the images for emotional quality. It was found that there was no change in the rating of positive or negative themed photos but there was a great increase in the negative rating of the neutral photographs. The negative rating also increased with the larger amount of time the person was sleep deprived. So when a person interacts with a neutral themed object while sleep deprived, they will perceive it to be more negative than positive. In another experiment, individuals where asked to provide a response to a cartoon scenarios of various types of frustrating events. The researchers found that individuals who where sleep deprived for 2 nights showed an elevation in their tendencies to redirect the blame toward other characters for causing the hypothetical event and also were less willing to offer amends. In conclusion, ones perception is effected through the negative mood caused by sleep deprivation.
1.4 Effects on Memory
Sleep is very critical for learning and memory. It is believed that if your sleep is negatively impacted, than memory processing is likewise degraded. Sleep is important for memory in two different ways. Firstly, sleep is important before learning or encoding of information occurs. This allows the brain to be prepared to properly obtain the new information. An experiment that demonstrates the importance of this preparation involves the examination of the effects of sleep deprivation on memory of different words differing in emotional value. Half of the participants were deprived of sleep for 36 hours while the other half were allowed to sleep. They both then completed an incidental memory-encoding task, which included words that were emotionally positive, negative or neutral. Then all participants were allowed to sleep for two nights and then under went a recognition test. Participants that where sleep deprivation, scored 40% more impaired in the recognition when compared to those who slept normally.This shows that sleep is important for memory encoding. This experiment also showed that the retention of the negative words was not impacted by the loss of sleep. However, sleep deprivation significantly impacts the encoding and retention of positive and neutral stimuli. Within the experiment, sleep deprived participants were 59% more impaired than those who slept in the recollection of positive and neutral words. Thus there is a favouring of negative memories over neutral and positive ones when one is sleep deprived.
Secondly, sleep is important for learning to facilitate consolidation and integrate the newly learned information into existing memory stores. For more information please see Sleep-Dependent Memory Consolidation.
Lastly, neuro-imaging has shown the areas effected during the encoding and recollection of information when one is sleep deprived. Participants of the experiment were sleep deprived for one night and than asked to memorize a photograph while undergoing an fMRI. Then after two nights of regular sleep, they were requested to recall the photograph from before while undergoing the fMRI again. They then compared the results to those who slept normally in this experiment. They found that during encoding there is less activity occuring in the posterior hippocampus when a person is sleep deprived. However, during recollection there is significantly lower activation in the anterior hippocampus.
1.5 Effects on Decision Making
|Example of the high-risk decision.|
Decision-making does not rely on cold cognitive processes, but it is actually based on emotional factors. However, these emotional factors can negatively influence a person’s decisions especially if a person is suffering from sleep deprivation, for people who are sleep deprive suffer with melancholy like moods. In the case of making decisions that are risky such as gambling, a person suffering from sleep depression is more likely to take much higher risks than normal. In one experiment, individuals where sleep deprived for 49 hours, where they where then place in a situation of a emotionally guided gambling task that assessed the willingness of one to take risks. Normally rested individuals gradually learn to avoid using the exciting high-risk deck and choose to use the modest deck that gives a constant pay off. After 2 nights sleep loss (49 hours), the people who once only stuck to the modest deck went back to high-risk deck even when faced with the long-term losses. However, further studies showed that the choice of deck also depends how the outcome is framed. If an outcome is presented in terms of a potential gain, sleep-deprived people are more likely to take risks then they ordinarily would. However, if the outcome is framed in terms of a potential loss, those who are sleep deprivation will not use the high-risk deck. It is thought that the expectation of grains or loss interacts with the reward regions of the brain. When sleep deprived, individuals make risky decisions there is an increased activation of reward centers, consistent to the expectation of gains. But sleep deprived individuals who have experienced losses; they show a reduction of activity in brain regions associated with aversion and punishment.
Sleep deprivation has a significant effect on social-emotional decisions that have implications for social exchange and morally relevant behavior. In this experiment one will go under a series of social exchanges and trust games with actual financial consequences. When the individual is sleep deprived for 36 hours, the person becomes more aggressive during social exchange, is reduced willingness to trust any unknown, even though it would benefit then both. A person who is sleep deprived will reject anything they considers unfair even if it means losing money in the process.