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G. Ficca, MD, PhD Sleep Laboratory, Department of Psychology II University of Naples

Sleep and cognitive functions. G. Ficca, MD, PhD Sleep Laboratory, Department of Psychology II University of Naples gianluca.ficca@unina2.it. General outline. Definition of the field Effects of sleep changes on alertness/vigilance Effects of sleep changes on higher cognitive functions

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G. Ficca, MD, PhD Sleep Laboratory, Department of Psychology II University of Naples

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  1. Sleep and cognitive functions G. Ficca, MD, PhD Sleep Laboratory, Department of Psychology II University of Naples gianluca.ficca@unina2.it

  2. General outline Definition of the field Effects of sleep changes on alertness/vigilance Effects of sleep changes on higher cognitive functions Theoretical and methodological remarks

  3. How are sleep and cognitive functions related to each other ? • Cognitive activity affects subsequent sleep • Cognitive processes duringsleep (dream, learning) • Effects of sleep changes on cognitive functions during subsequent wakefulness School performance, age-related impairments Work and car accidents Important for: Clinical symptoms in sleep disturbances

  4. Research on sleep effects on cognitive functions has to take into account several factors: SUBJECTS-RELATED Men, women Infants, toddlers, adults, elderlies Owls, larks Long sleepers, short sleepers FUNCTION-RELATED Vigilance Psychomotor performance Higher cognitive functions Subjective well-being CONTEXT-RELATED Experimental (deprivations, extensions) Naturalistic (shift works, life styles) Clinic (sleep pathologies) TIME-RELATED Occasional vs. cumulative sleep debt

  5. How much sleep do we need? The debate: Webb W.B. & Agnew H.W. ARE WE CHRONICALLY SLEEP DEPRIVED ? Bull. Psychon. Soc., 1975, 6: 47-48 Bonnet M. & Arand D. WE ARE CHRONICALLY SLEEP DEPRIVED Sleep, 1995, 18: 908-911 ------------------------------------------------------------------------------- Harrison Y. & Horne J. SHOULD WE BE TAKING MORE SLEEP ? Sleep, 1995, 18: 901-907

  6. How much sleep do we need ? = To what extent can sleep be curtailed without relevant cognitive impairment ?

  7. What does the notion of “cognitive impairment” include? Objective sleepiness All those signs indicating a tendency towards sleep. Detected through behavioral (yawning, dozing off, eye blinking) and/or EEG (alpha, theta frequencies) signs Measured through Multiple Sleep Latency Test (MSLT) or Maintenance of Wakefulness Test (MWT) Subjective sleepiness The individual feeling of being drowsy Measured through scales such as Karolinska Sleepiness Scale (KSS) or Stanford Sleepiness Scale (SSS) Reduced psychomotor performance Reduced speed. Reduced accuracy (lapses and mistakes when performing) Measured through either simple (Psychomotor Vigilance Task) or complex batteries (e.g., driving simulators or flight simulators) Impaired higher cognitive functions Measured through more specific tasks, such as Random Letter/Number Generation, basically aimed to evaluate prefrontal cortex effectiveness.

  8. Schmidt et al., 2007, Cogn. Neuropsychol., 2007, 24, 755-789

  9. Classical reviews (Wilkinson, 1965; Webb, 1969; Naitoh, 1975) • The effects of sleep deprivation on human physiology would be rather marginal. • Vigilance would be surprisingly resistent to sleep deprivation. Only curtailments to less than 4-hours’ sleep would affect vigilance, given that long and monotonous tasks are used. Methodological flaws: small sample size, inadequate control of sleep-wake schedules

  10. Vigilance and sleep duration: an exponential function ? Härmä et al., J Sleep Res. 1998, 7:167-74

  11. Effects of sleep deprivation on vigilance (1)

  12. Effects of sleep deprivation on vigilance (2)

  13. Van Dongen et al., 2003 The effects of cumulative sleep debt Belenky et al., 2003

  14. Does the brain adapt to neurobehavioral sleep loss consequences ? Belenky et al, J. Sleep Res. (2003) 12, 1–12

  15. Summary • Since the nineties, research has consistently foundclear negative effects on vigilanceafter one single 4-hours’ sleep. Many studies have shown such effects after nights with even 5 or 6 hours’ sleep. • Sleep duration seems the crucial factor, whereas less relevant would be the single sleep states (SWS and REM) contribution. • However, also sleep continuity might play a role. Infact, negative effects are found in experimental sleep fragmentation studies (Bonnet et al., 1987,1989, 2000), even without behavioural awakenings or changes in Slow Wave Sleep amount

  16. More controversial are the data on the effects of one night total sleep deprivation on psychomotor performance. • According to Pilcher & Huffcut (1996), the cognitive consequences are modest. • Instead, the impairment of cognitive functions when sleep debt accumulates over days or weeks is very relevant. • Adaptive changes are hypothesized to restrict brain operational capacity and to persist for several days after normal sleep duration is restored, delaying recovery

  17. Schmidt et al., 2007

  18. What are executive functions for ? (Sagaspe et al.,2006) Complex executive functions, including executive attention, working memory and divergent thinking involve the ability: to plan and coordinate willful action in front of alternatives; to monitor and update actions as necessary; to suppress distracting material by focusing attention on relevant information (a process called “inhibition”). Thus, beyond vigilance and the simplest operative skills, complex cognitive functions allow individuals to cope with responsibilities as well as with difficult, and frequently unfamiliar, tasks, through “decision making” and “problem solving” processes.

  19. Increased Adenosine SLEEP DEBT Frontal Lobe dysfunctions Reduced cortical cholinergic activity Harrison & Horne, 2000; Boonstra et al., 2007 PET studies One single night of sleep loss significantly reduces prefrontal metabolic activity Thomas et al., J Sleep Res, 2007, 9: 335-352

  20. Sleep deprivation and response inhibition Drummond et al., J Sleep Res, 2006, 15: 261-25 THE GO-NoGO PARADIGM

  21. Sleep deprivation andRandom Number Generation Gottselig et al., J Sleep Res, 2006, 15: 31-40

  22. Sleep deprivation and decision making Rested baseline vs. 49.5 hrs sleep deprivation Iowa Gambling Task Killgore et al. J Sleep Res, 2006, 15: 7-13

  23. Sleep deprivation and planning One night sleep deprivation PVT Six Elements Task: 3 tasks with 2 subtasks never to do consecutively BUT Nilsson et al., J Sleep Res, 2005, 14: -6

  24. SUMMARY Sleep deprivation paradigms have shown a negative impact of sleep debt on a number of complex neurocognitive functions, including inhibiting prepotent responses, decision-making and planning. Some degrees of cognitive impairment, concerning specific attentional and executive functions, can be found in otherwise alert and well-performing subjects. However: Also some reliable negative findings have been reported: Sagaspe et al.: no effect of 36 h TSD on Stroop interference Binks et al., 1999: no effect of 34-36 h TSD on inhibition Heuer et al., 2005: limited effects on Random Number and Nouns Generation

  25. Theoretical and methodological issues of interest • Vigilance and performance have to be measured several times during the day in order to control for the effects of circadian fluctuations, sleep inertia and overtime reduction of vigilance due to homeostatic reasons.

  26. Vigilance as a function of previous sleep duration and time of day Akerstedt et al., 1994

  27. Theoretical and methodological issues of interest • Vigilance and performance have to be measured several times during the day in order to control for the effects of circadian fluctuations, sleep inertia and overtime reduction of vigilance due to homeostatic reasons. • It is necessary to keep distinct the subjective and the objective domains

  28. Objective vs. subjective Van Dongen et al., Sleep. 2003, 26: 117-26

  29. Objective vs. subjective Partial sleep deprivation TST = 5 hrs (2-7) RLGT every 2 hrs the following day No relevant difference in subjective sleepiness levels for the nap vs. the wake group More errors in the wake group at the noon and evening points. NAP D’Onofrio et al., in preparation

  30. Theoretical and methodological issues of interest • Vigilance and cognitive functions have to be measured several times during the day in order to control for the effects of circadian fluctuations, sleep inertia and over-time reduction of vigilance due to homeostatic reasons. • It is necessary to keep distinct the subjective and the objective domains • Extreme etherogeneity of the neurocognitive batteries.

  31. What should we consider in neuropsychological testing? • Task difficulty • Task novelty • Reliability • Ecological validity • Repeatability • Time on task COMPLETENESS and FEASIBILITY

  32. Theoretical and methodological issues of interest • Vigilance and cognitive functions have to be measured several times during the day in order to control for the effects of circadian fluctuations, sleep inertia and over-time reduction of vigilance due to homeostatic reasons. • It is necessary to keep distinct the subjective and the objective domains • Extreme etherogeneity of the neurocognitive batteries. Focus on interindividual differences !!

  33. High sleepability • The ability (attitude) to easily fall asleep, expressed by a short sleep latency, unregarding: • Homeostatic factors • Circadian factors • Enviromental factors (Harrison & Horne, 1994)

  34. Interindividual differences Because of the well-known interindividual differences in sleep patterns (e.g., chronotypologies), “within-groups” designs are particularly suitable for this kind of research. (…) as large individual differences do exist in the need for sleep, the search for the sleep need may be vain. A somnotypology, taking into account age, gender and the position in both the sleep-alert and the morningness-eveningness continuum, should help in the search for the actual individual sleep need”.(Ferrara & De Gennaro, Sleep Med Rev, 2001)

  35. Effects of sleep extension on vigilance A 10-14 light-dark cycle, resulting in TST exceeding 8-8.5 hrs. significantly improves subjective mood, energy and fatigue Wehr et al., Am J Physiol, 1993

  36. Effects of naps on alertness and performance in sleep-deprivedsubjects Bonnet, 1991 2, 4 h naps Improvement in alertness (MSLT) over 48h continuous operation, linearly related to the length of nap Preserve baseline performance level over 64h continuous operation, while performance declines in control group Naitoh et al., 1994 20’ naps Takahashi & Arito, 2000 Under prior sleep loss, lower sleepiness and higher accuracy in logical reasoning in nap group than in wake control group 15’ nap Brooks & Lack, 2006 Under sleep restriction, 10’ was overall the most effective duration, in terms of latency and of duration of postnap restorative effects 30’, 15’, 10’, 5’ naps

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