Introduction
In daily life, individuals face many things which are mostly part of their jobs and routine life. These habits can affect their physical and cognitive performance in which all these things can be repaired by effective sleeps. However, when individuals faced plenty of stimulants during or before sleep, it can cause detrimental effects on cognitive performance especially in attention memory due to sleep restriction. At this point, two main terms become important which are acute total and chronic partial sleep deprivation (Alhola & Polo-Kantola, 2007). Although chronic partial sleep restriction is prevalent one and can be mimic of the condition occurring in the real life, acute total sleep deprivation can be transformed into chronic one and has gained more attention in a lot of studies (Alhola & Polo-Kantola, 2007). Several factors such as age, gender, interindividual responses and so on simultaneously play important roles in these phenomenon (Alhola & Polo-Kantola, 2007). Although they seem pretty similar at a first glance, they have bunch of differences especially in terms of cognitive recovery (Alhola & Polo-Kantola, 2007). In this paper, by centering sleep deprivation issue as main topic, we will give important examples on attention related research from previously published papers.
Sleep, Sleep Loss and Underlying Mechanism Behind
Sleep is essential need for body regulation such as main metabolism functions, some tissue recovering and regulations. Sleep varies around 7-8.5 h per day (Alhola & Polo-Kantola, 2007). As long as sleep is not adequate, body and cognitive function will be lost such as impaired immune response, unexpected mood transitions, increased insulin resistance, endocrine abnormalities and so on.
Sleep basically consists of two sections. First is homeostatic process S which runs as long as sleep is needed. Another is circadian process C which is responsible for adjusting threshold between starting and completing point of sleep. This model is essential for examining and defining of sleep deprivation studies (Alhola & Polo-Kantola, 2007).
Many hypotheses have been developed to reveal mechanism behind sleep loss effects regarding cognitive performances. These theories based on briefly two approaches (i) general and (ii) selective. General approaches are proposing that sleep deprivation has general effects on alertness and attention. Other one is related with selective effects on brain structures and cerebral functions (1). Besides, interindividual responses can be included to these approaches (Alhola & Polo-Kantola, 2007).
According to general approaches, cognitive deteriorations is directly correlated with alertness and attention which assessed three different point of views like lapses, slowed responses and wake state instability (Alhola & Polo-Kantola, 2007). Lapses, in other words, short period of time of inattentiveness, are most crucial phenomena in cognitive impairments according to on lapse theory (Alhola & Polo-Kantola, 2007). Even ifcognitive performances are supposed to be steady between lapses measured by EEG activity, it can be slowed down independent from lapses. As a result of these, individual performance during sleep deprivation through vigilance can be declined especially in their duties which require long working hours and routine simple handling (Alhola & Polo-Kantola, 2007). Apart from lapses and slowing response, wake state instability view reflects that fluctuations in alertness and effort can cause decreased performance during sleep deprivation (Alhola & Polo-Kantola, 2007).
Regarding selective effects, impaired cognitive performance is related with brain functions and assume that sleep deprivation effects prefrontal cortex which is responsible for language, creativity, thinking and other higher functions and finally diminish the cognitive performances. According to this theory, main reason of individual performance is about getting bored during working hours because of simple jobs with long working hours. Several methodologies measure brain functions against sleep deprivation have been developed so far such as functional magnetic resonance imaging and positron emission tomography but higher methods are required not only measure working memory and attentional functions (Alhola & Polo-Kantola, 2007).
Individual sleep duration, length and structure can differ each other. Thus, their response to sleep deprivation can be different and worth a measure this. At this point, trait-based vulnerability against sleep loss can be good marker (Alhola & Polo-Kantola, 2007).
Acute Total Sleep and Chronic Partial Sleep Deprivation Regarding Attention and Working Memory
As mentioned before, acute total sleep deprivation has gained attention and attention and working memory are investigating at this point. There are plenty of reasons why these are crucial for sleep deprivation. Considering brain functions, not only attention but also working memory are harmed in inadequate sleep because they are associated with frontal lobes which is not robust against sleep deprivation (Alhola & Polo-Kantola, 2007).
Partial sleep restriction better reflects real life condition than acute total sleep deprivation. If partial and total sleep restriction are allowed to compare, it will be hard because of methodologies among studies especially in applied length of sleep restriction and cognitive points considered (Alhola & Polo-Kantola, 2007).
Cognitive Recovery
Some evidences are still not clear how recovery of cognitive performance occurred after sleep restriction. Some studies proved that if sleep is happened once at least 8 hours, detrimental effects of sleep deprivation on cognitive performance can be destroyed (Alhola & Polo-Kantola, 2007). Besides, recovery durations between acute and chronic sleep deprivation are different from each other so chronic partial restriction may take more much time than acute total restriction (Alhola & Polo-Kantola, 2007). These traits depend on interindividual differences, age, gender as well (Alhola & Polo-Kantola, 2007).
Experiment Design
To assess sleep deprivation, as previously mentioned, two models have taken into account. Human subjects are stayed up for 24-72 h for acute total sleep deprivation experiments as their sleeps interrupted regularly during several consecutive nights for chronic partial sleep deprivation (Alhola & Polo-Kantola, 2007).
Psychomotor Vigilance Test is commonly used for working memory and attention evaluation against sleep deprivation. It is highly susceptible test for sleep loss and it gives an information about reaction speed and lapses.
To measuring attention and working memory, some obstacles should be overcome such as small sample size, sleep history of subjects, usage of some stimulants before experiment, neglection of commands, long duration, ineffective signal rates (Alhola & Polo-Kantola, 2007).
Speed and accuracy two essential points in terms of experimental design. Most studies have divergent data and are controversial each other because of tradeoff of speed and accuracy. Unfortunately, it can be pretty hard to combine them equally because they are influenced by age, gender and interindividual responses (Alhola & Polo-Kantola, 2007).
Effects of Age, Gender, Interindividual Differences and Methodology
Age is really crucial parameter in several studies. According to most of studies, older people can better tolerate wakefulness than young people. Based on dividing attention and cognitive performance in several aspects, aging subjects show better performance at least they remained stable than young subjects against sleep deprivation (Alhola & Polo-Kantola, 2007). Because of biased data, the differences between young and aging subjects are still unknown and controversial in terms of performance.
In speed, however, overall aging subjects keep their performances and cognitive recovery better with sleep restriction than young subjects. This might be explained with decreasing of circadian progress in aging subjects. In other words, homeostatic processes and abundant exposing to wakefulness in young people result in chronic partial sleep deprivation. Therefore, it makes aging subjects vigilant constantly and recover progress takes a much more time in young subjects when compared to aging subjects (Alhola & Polo-Kantola, 2007).
Although women are suffering sleep problems much more than men, in most of aspects men are more vulnerable to sleep deprivation than women except recovery process. There are many reasons in parallel with this such as physiology, sex hormones through neuro and vascular pathways, brain structure, social behaviors and so on. However, considering attention, studies showed no significant differences between men and women. Another interesting research revealed whether hormone influence on sleep deprivation or not so it referred as difference between genders because hormones were usually used for woman to maintain their menstruatic loop. It concluded that there were no significant differences between users who get hormones and users who are hormone-free somehow. Of course, there are many hormones and different mechanisms of that like child bearing and nurturing etc. and it might result in different conclusions. Finally, the significant results are expected between genders because even brain structure and lifestyles are entirely different between them (Alhola & Polo-Kantola, 2007).
Last but not least point is that individual choice and methodologies. Actually, these parameters are connected with together in a way. Each individual is different from each other in all aspects such as sleep duration, circadian phase etc. Some of studies neglected while some of them attempted to normalize before one week for example. In parallel with individual choice, applied methodologies varies from research to research. Since this kind of research requires more expense and regular creativity, sleep deprivation studies are hard to observe and carry out. Inconsistency and unregular cognitive measures, lack of expertise of interpretation of data, choice of imaging techniques considering brain structure, inadequate experience in managing subject size and experiment scope such as small or huge group etc., area to allowed to sleep experiment, stimulants, complexity of tasks applied in cognitive tests can be included in general (Alhola & Polo-Kantola, 2007).
Research on Sleep in Deprivation and Attention
Doran, Van Dongen, and Dinges, (2001) in their research investigated the impacts of sleep deprivation on “state instability”. Basically, state instability reflects the effects of sleep deprivation on performance that relies on fundamental neurobehavioral processes. Since lapses are mostly occur in tasks required sustained attention, and lapse frequency on tasks is increased over time, an ability to sustain attention over time is an essential feature of vigilant tasks. Their experiment looked for answers to those questions (i) is there any evidence between increased performance variability (i.e, state instability) and interaction of homeostatic drive for sleep, (ii) is there any enhanced response variability in the presence of increasing compensatory effort to respond sleep loss, and (iii) how progression in sleep deprivation have impact on response slowing and lapsing? In sum, experiment tested the impacts of sleep deprivation on neurobehavioral performance including state instability which is particular evident in performance requiring sustained attention.
Twenty-eight healthy male subjects were separated into total sleep deprivation (TSD, N=13 with a mean age of 27,3) who underwent 88 hours of total sleep deprivation and NAP group (control, N=15, with a mean age of 28) who were given two hours nap opportunity once every twelve hours during 88 hours period of time. It is important to note that homeostatic drive in NAP group did not elevate as high as in comparison to TSD condition and therefore it is used as control. During the experiment, neurobehavioral testing such as psychomotor vigilance task (PVT) was applied. Subjects also responded several questions on computer monitors and results were analyzed. The differences in PVT performances among groups were compared. Results demonstrated that fast and error-free responding occurred during the first 16 hours of wakefulness in both groups. However, beginning from the 18 hours, TSD group showed progressive deterioration in performance. However, NAP group was able to maintain almost baseline performance during the experiment. Another finding suggested that inter-subject variability is increased as sleep deprivation is increased among TSD group. It means that some subjects have greater neurobehavioral impairment than others in terms of homeostatic drive for sleep. This is important point for inter-individual differences in response to TSD experiment. Another important finding showed that there are loss of stable performance and decreased attention with increasing sleep deprivation after one night of sleeplessness.
Results actually supported the hypothesis that state instability is being developed those who have sleep deprivation. In addition, subjects in TSD group demonstrated greater variability in performance as sleep loss progressed. This indicated that for individuals who spent awake time cumulatively demonstrated increased PVT variability in comparison to NAP group. Three potential outcomes of PVT variability may be speculated as (i) lapses, (ii) response errors and (iii) normal timely responses. Although these findings, this work has some limitation as well. This study did not apply neuroimaging applications to assess which part of the brain might be the responsible in state instability. Apart from that, in sum, results uncovered that sleep deprivation is increasingly variable events on sleep initiating mechanisms.
Chua, Fang, and Gooley, (2017) investigated divided attention performance during sleep deprivation by reasoning in which subjects will be having difficulties during dividing their attention across the given task. Basically, they improved their attention tasks from the previous research done by including visual and auditory cues. Therefore, sustained attention is required which is highly sensitive to sleep deprivation. Healthy males (N=30) with 25.8 ± 2.7 years mean age and standard deviation were recruited for the study. Ineligibility is based on history of shift work, travelling across time zones, and in response to their chronotype scores on the Horne-Östberg Questionnaire. Subjects further went to bed on their regularly time and after 8 hours of sleep, 40 hours of wakefulness was applied to participants. This process was named as constant routine procedure. Divided attention task was completed in 15 minutes of every 2 hours during the constant routine procedure. Task included auditory, visual and motor tracking stimuli. Results indicated that impaired divided attention performance occurred during exposure to sleep deprivation according to divided attention task. Performance on the auditory part of attention task was poorer when subjects were required to divide their attention to motor tracking and visual tasks. This effect appeared to be more prominent in exposure to sleep deprivation compared with rested wakefulness. In addition, multi-tasking responses were also impaired. Authors also applied Go/No-go stimuli in auditory task in which frequeny of these events may be involved in the impaired sustained attention rather than sleep loss on response inhibition and working memory since lower frequency of Go events were observed in comparison to No-go events. One limitation of this study is that observation of false negatives as much as false positives. Since cognitive processes are not limited to auditory, visual and motor tracking stimuli, additional studies and functional tasks are required to investigate this phenomenon. Another limitation in this study is that authors did not monitor sleep-wake state polysomnographically during the task was applied. Thus, it is impossible to identify response errors caused by falling asleep versus increased distractibility. This study has some implications as well. For instance, jobs such as air traffic controllers and healthcare personnel which requires to stay awake long working hours may have sleep deprivation and their ability to sustain attention might be impaired during exposure to sleep deprivation. Therefore, interventions in relate to improve sleep behavior, and development of technologies for automating tasks to reduce attentional failure in multi-tasking jobs for air traffic controllers might be an advantage to prevent attention related impairments in relate to sleep deprivation. All in all, divided attention performance is impaired in exposure to sleep loss.
Drummond, Gillin, and Brown, (2001) investigated cerebral responses during a divided attention task following sleep deprivation. Due to total sleep deprivation after normal tight sleep some cerebral disorders can be occur and observed by means of imaging techniques. In the previous dissertations, parietal lobe, left inferior frontal gyrus at BA 47 and prefrontal cortex were found to be activated with verbal task in normal and following 35 h total sleep deprivation whereas these activations declined in parietal lobe and prefrontal cortex during same conditions considered arithmetic performance (Drummond et al., 2000, 1999, see figure 1). In addition to previous studies, they established greater task to reveal connection between total sleep deprivation and divided attention. Four cognitive tasks in addition to verbal and arithmetic tests previously defined on divided attention applied on 13 control subjects divided 7 males and 6 females are around 27 years old as they sleep normally one night and without sleep at 35h. Subjects assessed according to memorizing ability and solving arithmetic problems quickly and correctly between tasks. Also, Stanford Sleepiness Scale and 5-point Likert Scales are utilized. The tasks basically evaluated individuals’ concentration on task, their behavior on task difficulty and quantified the effort during the task. As analyses were running with AFNI software, some criteria considered as following:
1) Blood oxygen level dependent signal and FMRI scans were assessed separately between nights
2) Cognitive task response compared one night and other.
3) Regression analyses performed to identify cerebral activation. They performed separately between memory and arithmetic tasks.
Figure 1: Representation of parietal lobe, prefrontal cortex and left inferior frontal gyrus at BA 47 within brain.
According to task results, the significant decrease was not observed in following total sleep deprivation comparing to normal sleep in terms of memory performance. According to behavioral data and self-report questionnaire, correct answers with serial subtraction between normal and sleep deprivation are not significantly different whereas incorrect answers shows reverse situation between normal and sleep deprived. This may be caused simply because of deficits on subject’s concentration that lack of sleep.
With respect to cerebral activation, 6 brain areas such as left inferior frontal gyrus BA 6/44, left middle temporal gyrus BA 21, left middle occipital gyrus BA 18/19, Right middle occipital gyrus BA 18/19, left inferior occipital gyrus BA 18/19, left cerebellum seems to activate in normal when analyzed separately. Despite of normal sleep, 11 brain regions within prefrontal cortex belong to both left and right hemisphere and parietal lobes activated in following total sleep deprivation when analyzed separately. Finally, 10 brain regions mostly in right prefrontal cortex are identically activated in total sleep deprived between normal and total sleep deprived nights whereas left promoter cortex BA6, right parahippocampal gyrus and left cerebellum regions are identically activated in normal sleep between normal and total sleep deprived nights. These results support that some brain regions involved in attention similar with verbal learning show relatively much more response without sleep than with sleep.
According to neuroimaginal data, it can be still unknown response to sleepiness between arithmetic and verbal learning. Since subtasks and their shifting each other can be vary but their cerebral activation are relatively higher without sleep than with sleep and show almost similar response in this paper.
Finally, when considering attention, brain seems to prepare some new sources against sleep loss and these sources activated when this situation is demanding. In doing so, it compensates some functional deficits and tries to make the regions that responsible for attention activate as if it is running with normal metabolism with adequate sleep.
Conclusion
Exposure to sleep deprivation was shown to impair attention in several tasks (Chua et al., 2017; Doran et al., 2001; Drummond et al., 2001) and has negative consequences such as impairment in cognition and performance. Therefore, individuals with specific jobs who expose sleep loss should take cautions and development of some technologies are required to prevent failure in the jobs of that specific population. Most of the sleep research apply attention tasks and neuroimaging studies to investigate the impact of sleep loss. Moreover, most of the research involve one of the approaches should be consider as limitation. Higher methods may also be required. In addition, since age, gender and interindividual differences may have impact on sleep, it is important to consider these influencers when research is done. In doing so, for instance, research generally use male subjects since female hormones may have impact on sleep. Even if males are used, inter-individual differences may create obstacles which may harden sleep studies. However, as mentioned, sleep deprivation impairs attention and cognition which is an important result of the researches mentioned here.
References
Alhola, P., & Polo-Kantola, P. (2007). Sleep deprivation: Impact on cognitive performance. Neuropsychiatric Disease and Treatment.
Chua, E. C.-P., Fang, E., & Gooley, J. J. (2017). Effects of total sleep deprivation on divided attention performance. PLoS One, 12(11), e0187098.
Doran, S. M., Van Dongen, H. P. A., & Dinges, D. F. (2001). Sustained attention performance during sleep deprivation: evidence of state instability. Archives Italiennes de Biologie, 139(3), 253–267.
Drummond, S. P. A., Brown, G. G., Gillin, J. C., Stricker, J. L., Wong, E. C., & Buxton, R. B. (2000). Altered brain response to verbal learning following sleep deprivation. Nature, 403(6770), 655.
Drummond, S. P. A., Brown, G. G., Stricker, J. L., Buxton, R. B., Wong, E. C., & Gillin, J. C. (1999). Sleep deprivation-induced reduction in cortical functional response to serial subtraction. Neuroreport, 10(18), 3745–3748.
Drummond, S. P. A., Gillin, J. C., & Brown, G. G. (2001). Increased cerebral response during a divided attention task following sleep deprivation. Journal of Sleep Research, 10(2), 85–92.
Terrific article