Sleep covers 1/3 of human life. During sleep, there are many changes in hormonal and chemical structures. With sleep, the body, and the brain find the opportunity to renew themselves. One of the most important requirements of living a healthy life is to sleep well, otherwise serious deficiencies are observed in our mental abilities [29]. Sleep deprivation is a serious problem that can disrupt the activity of the human brain, cause changes in brain structure and impairments in neurocognitive perforfman [25], [26], [12]. Today, sleep deprivation has become a common health problem in clinics [33]. It is reported that adults slept 9 hours a day in the early 1900s and 7 hours a day in later years, but today individuals sleep significantly less than in the past [33]. For the last 20 years, it has been known that especially the young population have poor sleep quality [3], [6], [35]. Considering the sleep quality in Turkey, the prevalence of poor sleep quality was reported as 55.1% [15].
There are important activities on the prefrontal cortex (PFC) in the brain during sleep. Compared to all other cortical regions, frontal cortical activity has the highest voltage during non-REM sleep. It is also known that dreaming occurs with forebrain structures. This region plays an important role in sleep physiology, dreaming and sleep deprivation [37].
PFC is responsible for the higher mental processes that distinguish humans from other living things; these higher mental functions are known as executive functions. These abilities are of vital importance such as determining and maintaining purposeful behavior, planning, strategy making, decision making, memory, and attention. PFC undertakes high-level human functions and is indispensable for success in a chaotic world and stands out as a connecting point for performing many of these highest and most complex cognitive processes [16], [25]. The dorsolateral part of the PFC, that is, the dorsolateral prefrontal cortex (DLPFC), appears to be responsible for these high-level abilities [43].
Data obtained from related studies also emphasize that PFC is particularly sensitive to sleep, and frontal executive functions are affected due to sleep deprivation [12], [18], [37]. Daily human life confronts us with tasks related to this region and PFC may be tired due to overuse; therefore, it may be particularly vulnerable to the effects of sleep deprivation as cited in [27]. PFC carries out many vital functions, it is one of the areas that needs a healthy sleep the most to rest and rejuvenate. Studies also suggest that sleep deprivation leads to a reduction in the glucose metabolism of the PFC, reducing the 'fuel' of the structures that sustain cognitive processes [48]. Thus, sleep deprivation impairs mental performance and impairs the most sensitive of these functions, attention and executive functions. Moreover, even just 1 night of sleep deprivation is reported to cause impairment in executive functions [30]. Due to the effects of sleep deprivation on the PFC, there are serious deficits in decision making, flexible thinking, and inhibiting impulsive behaviors, as well as executive functions that the DLPFC is responsible [41].
Sleep deprivation disrupts the proper functioning of the PFC and causes serious disruptions in personal and social life [47]. Therefore, the tasks for which the region is responsible are also expected to be disrupted: these are executive functions.
Studies report another region most affected by sleep deprivation. This is the ventromedial part of the PFC: the ventromedial prefrontal cortex (VMPFC). Sleep problems have been associated with reduced gray matter in the VMPFC region and has been proven to impair the activity of this region as well. It has been demonstrated that people with sleep disorders such as narcolepsy, obstructive sleep apnea, and chronic insomnia have reduced gray matter volumes in VMPFC regions [26]. VMPFC activity changes significantly after sleep deprivation and increased daytime sleepiness and reduced gray matter in the left VMPFC were significantly associated [11], [26], [32], [52].
This component of the PFC appears to be responsible for critical abilities for social life. Consistent activations in the VMPFC related to social cognition and moral judgments [16], [28]. Social cognition and moral decision-making are interconnected [30]. Social cognition refers to the ability to understand the beliefs and intentions of other people in the social environment and to make predictions about intentions and behaviors. Through social cognition, certain norms are assigned for people, groups and roles with the information obtained about the environment [51]. Information obtained through social cognition contributes to moral cognition and moral decisions. Without these abilities, it would be impossible to maintain social relationships. Lack of these abilities are characterized by disorders such as autism spectrum disorder. Also, patients with VMPFC lesions are notorious for impaired decision-making, psychosocial dysfunction, and inappropriate behavior in the social environment [5].
It has been reported that the signals of decision values formed in the VMPFC change after sleep deprivation, and behaviors such as risk-taking increase after sleep deprivation [23], [25], [32], [36], [45]. Additionally, participants who experience sleep deprivation are more willing to act in violation of personal moral values [24]. These cognitive deficits can lead to riskier outcomes, especially in people working in critical professions [38]. However, there appears to be little interest in social and moral ability. Taking perspective is the main ability underlying social cognition. It has been stated in the limited studies that the participants ability to take the perspective of others regressed after sleep deprivation [13]. The results reveal that sleep deprivation causes poor performance in social cognition tasks [13]. [14].
As mentioned above, VMPFC appears to be responsible for social cognition and moral decision-making. Research has shown the significant effects of sleep deprivation on the VMPFC. It is predicted that the disruptive effect of sleep deprivation on the VMPFC will also lead to impairment of the tasks undertaken by the VMPFC; These tasks are social cognition and moral decision making.
When the relevant literature is researched, it is found that research findings are quite limited. Previous studies on sleep deprivation mainly investigated the effects specified period sleep loss by depriving healthy subjects and the results are remarkably similar: Sleep deprivation causes a decrease in performance [13], [20], [24], [30], [38], [47], [48]. However, these declines are temporary and now predictable.
In this study, the DLPFC and VMPFC regions of the prefrontal cortex, which are most affected by sleep deprivation, were featured. The reason for this is that it is the brain regions that show the most striking effects against sleep deprivation, and these two brain regions are responsible for the abilities that play a vital role in human life. Also, the side that provides convenience for research is the availability of measurement tools that measure the abilities of these regions and cause activation in these brain regions while being performed.
It is known that DLPFC is responsible for executive functions and VMPFC is responsible for moral decision making and social cognition. We combined this two information and investigated how these abilities are affected due to the negative effects of sleep deprivation on the brain. To our knowledge, this is the first study to evaluate executive functions, social cognition, and moral decision-making abilities in brain regions affected by sleep deprivation. To our knowledge, there is no other study evaluating how chronic poor sleep quality affects the functions that guide human life.