SLEEP AND COGNITIVE FUNCTIONS

Sleep is a complex physiological process that is regulated globally, regionally, and locally by both cellular and molecular mechanisms. It occurs to some extent in all animals, although sleep expression in lower animals may be co-extensive with rest. In the human beings occupies one third of the life. Sleep regulation plays an intrinsic part in many behavioral and physiological functions. A considerable number of hypothetical functions of sleep have been proposed, but none of the hypotheses under active consideration has gained enough experimental support to convince a preponderance of sleep researchers. What we know certainly is that sleep is essential for many vital functions including development, energy conservation, brain waste clearance, modulation of immune responses, cognition, performance, vigilance, disease, and psychological state.

What is the sleep

The classic definition of sleep is generally based upon physiological characteristics observed in mammals including reduced body movement and electromyographic activity, reduced responsiveness to external stimuli, closed eyes, reduced breathing rates, and altered body position and brain wave architecture.

Electrical brain activity occurs, in part, from ionic current changes within neurons and, to a lesser extent, some types of glia. Electrical brain activity is measure by a specific device able to convert electrical signals in wave:: electroencephalogram (EEG).

EEG signals are largely the product of synchronized synaptic currents generated by the apical dendrites of pyramidal neurons. Nevertheless, intrinsic membrane properties, neuronal firing, and glial activity likely also contribute to the EEG signals. EEG frequency bands provide essential information of how brain regions, cells, and molecules regulate wakefulness, sleep states, and display dysfunction due to related pathologies.

Moreover these wave happen in a specific part of the sleep: in a part of the sleep there is a unique phenotype characterized by rapid eye fluctuation movement, muscle atonia (with the exception of muscles that control eye movements, the heart, and diaphragm), and a rapid low voltage EEG, categorized as REMS: Rapid Eyes Movement Sleep.

The other state identified as NOREM (Non Rapid Eyes Movement Sleep), which is characterized by slow and high voltage EEG, and reduced heart rate and blood pressure; it is divided into three sub states. Human sleep cycles between NREMS and REMS for approximately 90 minutes for about four to five times during the night in an ultradian cycle1. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabella normale"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:none; text-autospace:none; font-size:12.0pt; font-family:"Times New Roman"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} table.TableNormal {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 0cm 0cm 0cm; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:none; text-autospace:none; font-size:11.0pt; font-family:"Times New Roman"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-ansi-language:EN-US; mso-fareast-language:EN-US;}  

Gross physiological characteristics of Wakefulness, NREMS and REMS.

Wakefulness

NREMS

REMS

Enhanced movement activity

Reduced movement activity

Reduced movement activity (cataplasia)

Opened eyes

Closed eyes

Closed eyes (rapid-eye movements)

Enhanced responsiveness to external stimuli

Reduced responsiveness to external stimuli

Reduced responsiveness to external stimuli

Variable body position

Recumbent body position

Recumbent body position

Variable breathing rate

Regular breathing rate

Variable breathing rate

From: AIMS Neurosci.2016;3(1):67–104.doi:10.3934 Functions and Mechanisms of Sleep Mark R. Zielinski1, James T. McKenna1, and Robert W. McCarley

Typically, human sleep is deeper in the beginning of sleep and REMS encompasses a greater proportion of the sleep cycle as sleep persists. It's important to remember that every vital function in the mammalian is regulated by cycles, and the sleep is not far behind. This is a basic rule when we need to take a care every disease.

Physiological parameters, of the human circadian rhythm ("biological clock")

The Body Clock Guide to Better Health" by Michael Smolensky and Lynne Lamberg; Henry Holt and Company, Publishers (2000).

Cognitive Functions and Sleep

The importance of sleep for learning and memory has been abundantly documented in animals and humans, and virtually everyone can attest to that when is deprived of sleep is in difficult to learn or to remember something. In recent years the neurophysiological mechanisms underlying the encoding of experience and its consolidation into long-term memory have been increasingly elucidated.

In experimental task, sleep deprivation generally results in a progressive degradation of the performance during extended tasks (fatigue effect) exacerbated by sleep loss. While tasks involving higher cognitive functions have been relatively less sensitive to sleep loss, possibly due to a higher level of engagement and compensatory effort, a large body of literature describes the consequences of sleep deprivation on sustained attention and other executive functions, procedural and episodic memory formation, and consolidation, as well as insight and creativity.

The effects of one night's total sleep deprivation were examined using the Wilkinson vigilance task and four 10 min duration performance tests. A repeated measures design was used in which eight male subjects experienced one night of sleep loss, the order of sleep loss being balanced across subjects. The four short duration performance tests consisted of choice reaction time, simple reaction time, short-term memory, and a motor task, handwriting. The results confirm the effects of one night's sleep deprivation on the vigilance task and also show that performance on the two reaction time tests was significantly impaired by the loss of sleep, but not at such a high level as for the vigilance.

The short-term memory test failed to show any adverse effects of sleep loss and similarly for the handwriting. The experiment shows that two portable and brief (10 min) performance tests are sensitive indices of sleep loss and should be particularly useful for assessing levels of alertness in the field 2.

In another experiment3 studying reaction time over 7 days of variable degrees of sleep restriction, sleep deprivation was shown to correlate with longer reaction time on PVT testing.

Longer reaction times were noted after only one night of sleep restriction (2 h of sleep reduction) compared to volunteers sleeping on average 8.5 h. Performance continued to diminish with each subsequent day and was directly correlated with the degree of sleep restriction. In the groups allowed to sleep for a maximum of 7 and 5 h, vigilance deficit stabilized after 5 nights, whereas in participants sleeping 3 h or less, vigilance continued to deteriorate in a linear fashion showing a twofold decrease compared to the control group at the end of the sleep restriction phase. After three nights with 8 h spent in bed, none of the sleep restriction groups returned to their baseline reaction times, suggesting that recovery from even mild sleep de-privation may last several days. This experiment also suggests that there may be an adaptive mechanism to mild and moderate chronic sleep deprivation (7 and 5 h groups) that may be insufficient to maintain performance levels in situations of severe chronic sleep deprivation (3 h group).

Other studies have confirmed the finding that impairment in PVT testing increases in proportion to the degree of sleep deprivation: Van Dongen, Maislin, Mullington, and Dinges studied the effects of chronic restriction of sleep periods to 4 h or 6 h per night over 14 consecutive days obtaining results in significant cumulative, dose-dependent deficits in cognitive performance on all tasks. Subjective sleepiness ratings showed an acute response to sleep restriction but only small further increases on subsequent days, and did not significantly differentiate the 6 h and 4 h conditions.

Polysomnographic variables and delta power in the non-REM sleep EEG-a putative marker of sleep homeostasis--displayed an acute response to sleep restriction with negligible further changes across the 14 restricted nights. Comparison of chronic sleep restriction to total sleep deprivation showed that the latter resulted in disproportionately large waking neurobehavioral and sleep delta power responses relative to how much sleep was lost. The conclusions of this study showed that chronic restriction of sleep to 6 h or less per night produced cognitive performance deficits equivalent to up to 2 nights of total sleep deprivation, it appears that even relatively moderate sleep restriction can seriously impair waking neurobehavioral functions in healthy adults. Sleepiness ratings suggest that subjects were largely unaware of these increasing cognitive deficits, which may explain why the impact of chronic sleep restriction on waking cognitive functions is often assumed to be benign. Physiological sleep responses to chronic restriction did not mirror waking neurobehavioral responses, but cumulative wakefulness in excess of a 15.84 h predicted performance lapses across all four experimental conditions. This suggests that sleep debt is perhaps best understood as resulting in additional wakefulness that has a neurobiological "cost" which accumulates over time4.

In a verbal learning task, the prefrontal cortex and parietal cortex were more activated after acute sleep deprivation. Interestingly, activation of the prefrontal cortex was positively correlated with the degree of subjective sleepiness, whereas activation in the parietal cortex was positively associated with the preservation of near-normal verbal learning. These patterns of increase and decrease in cerebral activation most likely represent compensatory adaptations (CA). In CA, more activation in the prefrontal cortex with acute sleep deprivation indicates a compensation process in response to the increased homeostatic drive for sleep. The prefrontal cortex is involved in working memory, attention and executive function, functions known to be vulnerable to sleep deprivation. On the other hand, activation of the parietal lobe with sleep deprivation indicates an adaptive process to support the decreased function of other areas of the cortex. These patterns of CA have task-specific differences and indicate that sleep deprivation can result in a combination of dysfunction and compensatory hyperfunction in the brain5.

A study about the involvement not only of prefrontal cortex in this deficit has been done with 33 men (mean age, 28.6 ± 6.6 years) scheduled for 3 functional magnetic resonance imaging scanning visits: an initial screening day (screening state), after a normal night of sleep (rested state), and after 30 hours of sleep deprivation (sleep-deprivation state). Subjects performed the Sternberg working memory task alternated with a control task during an approximate 13-minute functional magnetic resonance imaging scan. Neuroimaging data revealed that, in the screening and rested states, the brain regions activated by the Sternberg working memory task were found in the left dorsolateral prefrontal cortex, Broca's area, supplementary motor area, right ventrolateral prefrontal cortex, and the bilateral posterior parietal cortexes. After 30 hours of sleep deprivation, the activations in these brain regions significantly decreased, especially in the bilateral posterior parietal cortices. Task performance also decreased.

A repeated-measures analysis of variance revealed that subjects at the screening and rested states had similar activation patterns, with each having significantly more activation than during the sleep-deprivation state.

These results suggest that human sleep-deprivation deficits are not caused solely or even predominantly by prefrontal cortex dysfunction and that the parietal cortex, in particular, and other brain regions involved in verbal working memory exhibit significant sleep-deprivation vulnerability6.

Level of difficulty modulate the cerebral response, and interindividual differences can contribute to the difficulty of using neuroimaging studies as a generalized parameter of sleepiness. It has been demonstrated in fMRI studies that activation of the frontoparietal region was more robust in participants found to be less vulnerable to the effects of sleep deprivation. This suggests that more activated CA may correlate with less vulnerability to sleep deprivation. As mentioned, several aspects of executive function are affected by sleep deprivation. Sleep deprivation results in difficulty determining the scope of a problem in cases of distracting information and impairs divergent thinking and originality as measured on the Torrance Tests of Creative Thinking.

Although much is known about the impact of sleep loss on many aspects of psychological performance, the effects on divergent (“creative”) thinking has received little attention. Twelve subjects went 32 h without sleep, and 12 others acted as normally sleeping controls. All subjects were assessed on the figural and verbal versions of the Torrance Tests of Creative Thinking. As compared with the control condition, sleep loss impaired performance on all test scales (e.g., “flexibility,” the ability to change strategy, and “originality,” generation of unusual ideas) for both versions, even on an initial 5-min test component. In an attempt at further understanding of whether these findings might be explained solely by a loss of motivation, two additional short and stimulating tests were also used—a word fluency task incorporating high incentive to do well and a challenging nonverbal planning test. Performance at these tasks was still significantly impaired by sleep loss. Increased perseveration was clearly apparent. Apparently, 1 night of sleep loss can affect divergent thinking. This contrasts with the outcome for convergent thinking tasks, which are more resilient to short-term sleep loss7.

It's worth underline that Divergent thinking is a thought process or method used to generate creative ideas by exploring many possible solutions. It is often used in conjunction with its cognitive colleague, convergent thinking, which follows a particular set of logical steps to arrive at one solution, which in some cases is a ‘correct’ solution. Divergent thinking typically occurs in a spontaneous, free-flowing ‘non-linear’ manner, such that many ideas are generated in an emergent cognitive fashion. Many possible solutions are explored in a short amount of time, and unexpected connections are drawn. After the process of divergent thinking has been completed, ideas and information are organized and structured using convergent thinking.’ It's important to consider that divergent thinking is very useful in many critical situations like to think and escape plan.

Sleep deprivation also affects temporal memory, as shown by lower performance on tasks of recency (inability to recall the timing for recent events), even in conditions of preserved alertness with use of caffeine, and this is a very critical aspect in a military o police field where, always the use of caffeine is widespread to maintain the alert state.

Working memory is very important for the soldiers, and studies report some remarkable effects of cognitive training on Working Memory span, but before looking at that let’s get a handle on what Working Memory really means. Virtually everyone has heard of it, but most people mix it up with short term memory, like the ability to remember a phone number you just heard. Working Memory is very different. Although it does involve holding transient information, it’s really more about rapidly processing and manipulating it. Working memory is a cognitive system with a limited capacity that can hold information temporarily, and is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term memory, but some theorists consider the two forms of memory distinct, assuming that working memory allows for the manipulation of stored information, whereas short-term memory only refers to the short-term storage of information.

Component of Working Memeory

From: https://www.neurotrackerx.com/post/military-working-memory

In a working memory task under sleep deprivation, fMRI studies demonstrated decreased activation in the parietal region, and increased activation in prefrontal and thalamic regions in more complex tasks.

In a specific study about that, the neurobehavioral effects of 24 hr of total sleep deprivation (SD) on working memory in young healthy adults was studied using functional magnetic resonance imaging.

In the study of Chee and Chieh Choo, two tasks, one testing maintenance and the other manipulation and maintenance, were used. After SD, response times for both tasks were significantly slower. Performance was better preserved in the more complex task. Both tasks activated a bilateral, left hemisphere-dominant frontal-parietal network of brain regions reflecting the engagement of verbal working memory. In both states, manipulation elicited more extensive and bilateral (L>R) frontal, parietal, and thalamic activation. After SD, there was reduced blood oxygenation level-dependent signal response in the medial parietal region with both tasks. Reduced deactivation of the anterior medial frontal and posterior cingulate regions was observed with both tasks. Finally, there was disproportionately greater activation of the left dorsolateral prefrontal cortex and bilateral thalamus when manipulation was required. This pattern of changes in activation and deactivation bears similarity to that observed when healthy elderly adults perform similar tasks. These data suggest that reduced activation and reduced deactivation could underlie cognitive impairment after SD and that increased prefrontal and thalamic activation may represent compensatory adaptations. The additional left frontal activation elicited after SD is postulated to be task dependent and contingent on task complexity. These findings provide neural correlates to explain why task performance in relatively more complex tasks is better preserved relative to simpler ones after SD8.

Statistical activation maps of BOLD signal change for LTR and PLUS in RW and SD. Activations are projected onto the unfolded cortical surface of an individual volunteer's brain. Regions showing greater activation for PLUS than LTR for each state appear in the bottom panels.

From: J Neurosci. 2004 May 12; 24(19): 4560–4567. doi: 10.1523/JNEUROSCI.0007-04.2004. Functional imaging of working memory after 24 hr of total sleep deprivation

This is another example of CA.

Another function deteriorated by sleep deprivation is the decision-making. Experiments show that acute and chronic sleep deprivation results in more rigid thinking and perseverative errors with poor appreciation of an updated situation despite intact critical reasoning, loss of focus to relevant cues, and increased risk taking, possibly due to reduced functioning of the ventro-medial PFC. Few sleep deprivation (SD) studies involve realism or high-level decision making, factors relevant to managers, military commanders, and so forth, who are undergoing prolonged work during crises. Instead, research has favored simple tasks sensitive to SD mostly because of their dull monotony. In contrast, complex rule-based, convergent, and logical tasks are unaffected by short-term SD, seemingly because of heightened participant interest and compensatory effort. However, recent findings show that despite this effort, SD still impairs decision making involving the unexpected, innovation, revising plans, competing distraction, and effective communication. Decision-making models developed outside SD provide useful perspectives on these latter effects, as does a neuropsychological explanation of sleep function. SD presents particular difficulties for sleep-deprived decision makers who require these latter skills during emergency situations9.

To better understand the sometimes catastrophic effects of sleep loss on naturalistic decision making, Whitney, Hinson, Jackson, Van Dongen investigated effects of sleep deprivation on decision making in a reversal learning paradigm requiring acquisition and updating of information based on outcome feedback. Thirteen subjects were randomized to a 62-h total sleep deprivation condition. Twenty-six (22-40 y of age; 10 women).were randomized to a sleep deprivation or control condition, with performance testing at baseline, after 2 nights of total sleep deprivation (or rested control), and following 2 nights of recovery sleep. Subjects performed a decision task involving initial learning of go and no go response sets followed by unannounced reversal of contingencies, requiring use of outcome feedback for decisions. A working memory scanning task and psychomotor vigilance test were also administered.

Sleep deprived subjects, and not controls, had difficulty with initial learning of go and no go stimuli sets and had profound impairment adapting to reversal. Skin conductance responses to outcome feedback were diminished, indicating blunted affective reactions to feedback accompanying sleep deprivation. Working memory scanning performance was not significantly affected by sleep deprivation. And although sleep deprived subjects showed expected attentional lapses, these could not account for impairments in reversal learning decision making.

This study shows that sleep deprivation is particularly problematic for decision making involving uncertainty and unexpected change. Blunted reactions to feedback while sleep deprived underlie failures to adapt to uncertainty and changing contingencies. Thus, an error may register, but with diminished effect because of reduced affective valence of the feedback or because the feedback is not cognitively bound with the choice. This has important implications for understanding and managing sleep loss-induced cognitive impairment in emergency response, disaster management, military operations, and other dynamic real-world settings with uncertain outcomes and imperfect information.

Conclusions

Although we have not considered, in this article, critical function in endocrine, metabolic, and immune regulation (that probably they will be object of the another piece), sleep appears to play an active and important role in maintaining neurocognitive performance during wakefulness.

Lifestyle changes many times are responsible of sleep deprivation, but also pathological situation (example insomnia). We have to be aware that attention and working memory, but it also other cognitive functions such as long-term memory and decision-making are compromised and always these function are responsible of our behavior and choices, but above all are critical requirement in the high risk employment.

Bibliography

“Decreased Cortical Response to Verbal Working Memory Following Sleep Deprivation” - Qiwen Mu, MD, PhD, Ziad Nahas, MD, Kevin A. Johnson, Kaori Yamanaka, MD, Alexander Mishory, MD, Jejo Koola, Sarah Hill, Michael D. Horner, PhD, Daryl E. Bohning, PhD, Mark S. George, MD - Sleep, Volume 28, Issue 1, January 2005, Pages 55–67, https://doi.org/10.1093/sleep/28.1.55

“Effects of sleep deprivation on short duration performance measures compared to the Wilkinson auditory vigilance task” -. M Glenville, R Broughton, A M Wing, R T Wilkinson - PMID: 756060 DOI: 10.1093/sleep/1.2.169

“Functional imaging of working memory after 24 hr of total sleep deprivation” - Michael W L Chee , Wei Chieh Choo - PMID: 15140927 PMCID: PMC6729385 DOI: 10.1523/JNEUROSCI.0007-04.2004

“Functions and Mechanisms of Sleep” - Mark R. Zielinski1, James T. McKenna1, and Robert W. McCarley - IMS Neurosci. 2016 ; 3(1): 67–104. doi:10.3934/Neuroscience.2016.1.67.

“How the Military Boosts Working Memory for Its Soldiers” www.neurotrackerx.com/post/military-working-memory

“The Body Clock Guide to Better Health" - Michael Smolensky, Lynne Lamberg; Henry Holt and Company, Publishers (2000)

“Sleep Homeostasis and the Function of Sleep” - Joel H. Benington www.researchgate.net/publication/12243399_Sleep_Homeostasis_and_the_Function_of_Sleep

“Sleep Loss and “Divergent” Thinking Ability” - J. A. Horne - Sleep, Volume 11, Issue 6, September 1988, Pages 528–536, https://doi.org/10.1093/sleep/11.6.528

“The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation” - Hans P A Van Dongen, Greg Maislin, Janet M Mullington, David F Dinges -PMID: 12683469 DOI: 10.1093/sleep/26.2.117

“The Functions of Sleep and the Effects of Sleep Deprivation” - E.H. During,, M. Kawai

“The Function(s) of Sleep” - Normal.dotm 0 0 1 5 30 dottore davide perego 1 1 36 12.0 0 false 14 18 pt 18 pt 0 0 false false false /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabella normale"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:none; text-autospace:none; font-size:12.0pt; font-family:"Times New Roman"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} Marcos G. Frank , H. Craig Heller - Chapter in Handbook of Experimental Pharmacology · January 2018

“The impact of sleep deprivation on decision making: a review” - . Y. Harrison, J. Horne - Psycholog Medicine Journal of experimental psychology. DOI:10.1037/1076-898X.6.3.236Corpus ID: 15306015

The Oxford English Dictionary

1In chronobiology, an ultradian rhythm is a recurrent period or cycle repeated throughout a 24-hour day. In contrast, circadian rhythms complete one cycle daily, while infradian rhythms such as the human menstrual cycle have periods longer than a day. The Oxford English Dictionary's definition of Ultradian specifies that it refers to cycles with a period shorter than a day but longer than an hour (Oxford English Dictionary).

2 Effects of sleep deprivation on short duration performance measures compared to the Wilkinson auditory vigilance task.

M Glenville, R Broughton, A M Wing, R T Wilkinson PMID: 756060 DOI: 10.1093/sleep/1.2.169

3The Functions of Sleep and the Effects of Sleep Deprivation E.H. During,, M. Kawai

4 The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation Hans P A Van Dongen , Greg Maislin, Janet M Mullington, David F Dinges PMID: 12683469 DOI: 10.1093/sleep/26.2.117

5The Functions of Sleep and the Effects of Sleep Deprivation E.H. During,, M. Kawai

6 Decreased Cortical Response to Verbal Working Memory Following Sleep Deprivation Qiwen Mu, MD, PhD, Ziad Nahas, MD, Kevin A. Johnson, Kaori Yamanaka, MD, Alexander Mishory, MD, Jejo Koola, Sarah Hill, Michael D. Horner, PhD, Daryl E. Bohning, PhD, Mark S. George, MD Sleep, Volume 28, Issue 1, January 2005, Pages 55–67, https://doi.org/10.1093/sleep/28.1.55

7 Sleep Loss and “Divergent” Thinking Ability J. A. Horne Sleep, Volume 11, Issue 6, September 1988, Pages 528–536, https://doi.org/10.1093/sleep/11.6.528

8 Functional imaging of working memory after 24 hr of total sleep deprivation Michael W L Chee , Wei Chieh Choo

PMID: 15140927 PMCID: PMC6729385 DOI: 10.1523/JNEUROSCI.0007-04.2004

9 The impact of sleep deprivation on decision making: a review. Y. Harrison, J. Horne Published 2000 Psycholog Medicine Journal of experimental psychology. Applied DOI:10.1037/1076-898X.6.3.236Corpus ID: 15306015