Sleep & Brain Health

Transcription

1 The Neuroscience School Sleep & Brain Health 2017 The Neuroscience School Sleep plays a vital role in good health and well-being throughout our life. Getting enough quality sleep at the right times can help protect our mental health, physical health, quality of life, and safety. The way you feel while you're awake depends in part on what happens while you're sleeping. During sleep, your body is working to support healthy brain function and maintain your physical health. In children and teens, sleep also helps support growth and development. The damage from sleep deficiency can occur in an instant (such as a car crash), or it can harm you over time. For example, in addition to raising your risk for some chronic health problems, not getting enough sleep can also affect how well you think, react, work, learn, and get along with others. Unfortunately, in our western society, people want to squeeze more out of their day and sleep is being treated as a commodity that can be traded for other activities.

2 By NoNameGYassineMrabetTalk fixed by Addicted04 [GFDL ( or CC BY-SA 3.0 ( creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons 2 There is a variety of biological mechanisms in place that modulate levels of wakefulness and help to induce sleep at the appropriate times. Chief among these regulatory mechanisms is a person's circadian rhythm, commonly referred to as the 'biological clock, that operates on a 24-h clock. This 24-h period is the time it takes the earth to rotate around its own axis which generates daily environmental cycles of ambient temperature and illumination. The alternation of light and darkness directly entrains an organism s circadian rhythms and influences its life patterns, creating species that are active primarily during the light (diurnal) or the dark (nocturnal) periods. This diagram depicts the circadian patterns typical of someone who rises early in the morning, eats lunch around noon, and sleeps at night (going to bed at about 10 p.m.). Although circadian rhythms tend to be synchronized with cycles of light and dark, other factors - such as ambient temperature, meal times, stress and exercise - can influence the timing as well. Brain regions such as the reticular formation are able to maintain a general sense of the current time, and based on this information, related brain areas will activate different internal systems at different times of the day. These systems in turn exert their effects by secreting hormones, changing cardiovascular function, altering metabolic rates, etc. Much of the circadian system's cyclical patterns are informed by the light levels it detects in the outside environment, so that exposure to artificial light may cause it to assume it is earlier than it actually is, and vice versa with artificial darkness. In terms of sleep, the circadian rhythm most prominently exerts its effects by regulating the secretion of the hormone melatonin. In response to dimming light levels, the suprachiasmatic nucleus of the hypothalamus triggers the release of melatonin, which then begins a cascade of events leading to ever-increasing drowsiness and ultimately sleep.

3 By Kernsters (Graph created in Paint) [GFDL ( or CC BY-SA 3.0 ( creativecommons.org/licenses/by-sa/3.0)], via Wikimedia 3Commons To initiate sleep, brain activity has to be gradually slowed to the point at which it drops below the threshold of consciousness. Over the course of a night, brain activity fluctuates between several distinct phases. After declining down to the point of deep slow wave sleep, brain activity begins to cycle back up to a state which almost resembles a waking state. This phase is called REM sleep (short for Rapid Eye Movement, which is a peculiar characteristic of this phase) and shown in red here [click]. Physiological conditions like blood pressure surge back to approach waking levels as well, and activation of brain regions associated with motion forces the body to enter a state of temporary paralysis of the limbs. Eventually however, REM sleep will end, the body will return to NREM sleep (short for Non-Rapid Eye Movement sleep). Each progressive REM period becomes slightly longer as the body approaches its recommended amount of sleep, which, for reasons that will be discussed next, is essential both for feeling well-rested in the morning and for proper completion of the important biological functions going on during sleep. However, with the introduction of artificial light and other technologies, television and alarm clocks have replaced these natural signals and may affect optimal sleep duration. Additionally, industries that operate 24 h a day create light and noise that can interfere with sleep and require employees to work during hours usually devoted to sleep. And, with the increase in international business and air travel, many adults are frequently traveling across time zones which affects the circadian timing system. Thus, many humans are challenging basic biological pressures in order to accommodate social norms and obligations.

4 4 For most healthy adults, physiological sleep duration appears to range between 7.0 and 8.5 h; however, habitual sleep duration among adults is determined by a variety of factors and shows considerable variance within and between individuals. There is considerable debate as to whether or not sleep duration has been decreasing among adults in recent decades and if so, whether this reduction is resulting in higher rates of chronic sleep restriction or sleep debt. According to a 2008 Center for Disease Control Morbidity and Mortality Weekly Report, the percentage of adults who reported an average of less than or equal to 6 h of sleep within a 24-h period significantly increased from 1985 to 2004 (in both females and males and among all age groups 18 75). Studies have suggested that habitual short sleepers do not require less sleep than other adults; rather, these individuals gradually accrue sleep debt over time. Evidence from the American Time Use Survey shows that adults sleep significantly less during weekdays compared to weekends, suggesting that adults attempt to recover sleep debt by extending sleep when it is presumably more convenient and when schedules are likely more flexible.

5 5 These are the sleep time durations recommended by the National Sleep Foundation. The Foundation compiled a multidisciplinary expert panel comprised of both sleep experts and experts in other areas of medicine, physiology, and science to review the literature on sleep and come up with recommendations. For adults, they recommend between 7 and 9 hrs of sleep, although one hour on either side is also acceptable. Hirshkowitz, M., Whiton, K., Albert, S., Alessi, C., Bruni, O., DonCarlos, L., Hillard, P. (2015). National Sleep Foundation s sleep time duration recommendations: methodology and results summary. Sleep Health, 1(1), doi: /j.sleh

6 6 Although the physiological function of sleep is not completely understood, it is well documented that it contributes significantly to the process of learning and memory. Ample evidence suggests that adequate sleep is essential for fostering connections among neuronal networks for memory consolidation in the hippocampus. Sleep is an active phenomenon that incorporates brain regions involved in information processing during wakefulness. This is suggested by experiments that show an increase in sleep amount after learning and improved memory after REM sleep, together with the presence of certain waking brain activity patterns during REM sleep. Interestingly, current evidence suggests that sleep may be a privileged time window, free of interference from external sensory inputs, that allows the brain to consolidate newly acquired memories. Numerous studies show that sleep could contribute to the consolidation of memory and synaptic changes after the initial induction of plasticity during wakefulness. Sleep is a vital process linked to neural restoration and physiological maintenance across multiple systems. For example, healthy sleep is linked to clearance of metabolic waste from the brain and enhancement of cognitive function, including the consolidation of memory. Conversely, sleep loss is linked to a diverse range of adverse effects, including deficits in cognitive function and dysregulation of circadian processes, such as cortisol secretion. Further, poor sleep is implicated in impaired emotional function, including deficits in emotion regulation. Sleep disturbance is highly prevalent in psychopathology, and sleep impairments are found in almost every major psychiatric disorder. Cox, R., & Olatunji, B. (2016). A systematic review of sleep disturbance in anxiety and related disorders. Journal of Anxiety Disorders, 37, doi: /j.janxdis

7 7 Numerous studies have confirmed the beneficial effect of sleep on in various tasks. A period of post-learning sleep enhances our ability to retain declarative information and improves performance in procedural skills. Declarative memory is our memory for facts and events and is conscious whereas procedural memory is our memory for knowing how to do things and is unconscious. Sleep also supports the consolidation of emotional information. In one study, effects of a 3- hour period of sleep on emotional memory were even detectable 4 years later. Significant sleep benefits on memory are observed after an 8-hour night of sleep, but also after shorter naps of 1 2 hours, and even an ultra-short nap of 6 minutes can improve memory retention. However, longer sleep durations yield greater improvements, particularly for procedural memories. The optimal amount of sleep needed to benefit memory and how this might generalize across species showing different sleep durations is unclear at present. Some data suggest that a short delay between learning and sleep optimizes the benefits of sleep on memory consolidation. Diekelmann, S., & Born, J. (2010). The memory function of sleep. Nature Reviews Neuroscience, 11(2),

8 2017 The Neuroscience School 8 WHAT ARE THE CAUSES OF PARTIAL SLEEP RESTRICTION Work time may be the most potent determinant of sleep duration. Using a prospective study design, one recent study found that working more than 55 h/week is a risk factor for the development of shortened sleep and for difficulty falling asleep. Shift work creates a conflict between the worker s internal circadian time and his/her required sleep wake schedule, leading to impaired wakefulness and disturbed sleep. Commute/travel time can eat into sleep time. Leisure, especially screen time, also affects sleep. Computer and mobile phone use in the bedroom is associated with greater variability in sleep wake schedules and poorer sleep habits. In addition to the time used engaging in these activities, exposure to light emitted from these screens may also impede sleep. Blue (short wavelength) light is the most potent portion of the light spectrum for suppressing melatonin and promoting wakefulness. Exposure to blue light immediately prior to bedtime (via flat screen televisions, smartphones, and tablets) may cause circadian phase delays and disrupt sleep.

9 9 Although humans are diurnal, some individuals prefer activity in the morning (larks) whereas others prefer activity in the evening (owls) this preference influences the timing of sleep wake cycles. Morning-type and evening-type individuals differ endogenously in the circadian phase of their biological clocks, which is partially genetically determined. Age and gender also influence morningness eveningness. The Earth s light/dark cycle and the work schedules of industrial societies complement individuals who function best in the morning rather than in the evening. Owls experience heightened alertness in the late evening and typically stay awake longer and have a delayed bedtime compared to larks however, due to typical work schedules owls often use an alarm clock to wake up early in the morning, which produces chronic sleep restriction, extended wakefulness, and accumulated sleep debt during the work week

10 AMENCLINICSPHOTOS The Neuroscience School 10 The increased propensity for sleep due to restricted sleep time can lead to the occurrence of microsleeps. These re brief sleep episodes that intrude into wakefulness despite an individual s best effort to stay awake. The struggle between the increased propensity for sleep and needing to stay awake results in unpredictable behaviour, including increased variability in cognitive performance and lapsing (i.e., brief periods of half a second to many seconds of no response) that individuals may not realize they are experiencing. Sleep restriction can increase the incidence of micro sleeps and produce decreased behavioural alertness, even during goal-directed behaviours (e.g., driving). Behavioural alertness, measured using sustained attention tasks in the laboratory, has been shown to be sensitive to sleep restriction. When sleep is chronically restricted, sleep debt accumulates across each night leading to greater impairment over time. Thus, as the need for sleep increases, the brain s ability to maintain alertness becomes progressively more overwhelmed by the activation of sleep processes which leads to microsleeps and consequent neurobehavioural instability. Even when highly motivated, an individual s attempt to compensate for excessive sleepiness by engaging in various behaviours ultimately fails to prevent intrusions of microsleeps and impaired neurobehavioral performance. In the lab, studies have primarily focused on short-term sleep restriction and have found that driving performance on simulators decreases (resulting in more crashes) after short sleep duration (defined as 4 6 h TIB). Similarly, the less sleep obtained during chronic partial sleep restriction, the more driving performance (defined as the increase in number of driving simulator accidents) is impaired. Spaeth, A. M., Goel, N., & Dinges, D. F. (2012). Managing neurobehavioral capability when social expediency trumps biological imperatives. Prog Brain Res, 199, doi: /b

11 11 In addition to its negative effects on alertness, sleep deprivation degrades aspects of cognitive performance. The Psychomotor Vigilance Task is a measure of sustained attention. In any goal-directed behaviour, we need to be able to maintain our attention for a period of time. The PVT is a simple task where participants see a dot on a screen, and press a button when the dot arrives. The arrival of the dot is unpredictable so participants need to be vigilant. The task measures reaction time to press the button and errors of omission (not pressing the button when the dot arrives) or commission (pressing the button when the dot is not present). In this study by Gregory Blenkey and colleagues from the Walter Reed Army Institute of Research, 66 young to middleaged volunteers where assigned to 7 nights of 3h, 5h or 7h of sleep. You can see that the reaction time of those who were in bed for 9 hours [click] did not change across the study (E1 to E7 refers to the days of the experiment and R1 to R3 refers to recuperation days following 9 hours TIB). The reaction time of those who slept less than 9 hours decreased, and especially so for the those who slept only 3 hours [click]. You can also see that speed recovered somewhat between the 7th day of 3hrs of sleep and the first recovery night, but still remained below baseline even after 3 nights of recovery. This group did not fully recover after 3 nights of normal sleep. Speed was significantly lower for the other sleep-deprived groups too, and did not recover to baseline after 3 nights of normal sleep either. So you can see how chronic short sleep leads to a significant drop in attention that doesn t fully recover following 3 nights of normal sleep. Yet this is what many of us do, try to make up our sleep debt on the weekend. Belenky, G., Wesensten, N., Thorne, D., Thomas, M., Sing, H., Redmond, D., Balkin, T. (2003). Patterns of performance degradation and restoration during sleep restriction and subsequent recovery: a sleep dose-response study. Journal of Sleep Research, 12(1), doi: /j x

12 12 And the story is similar with regard to the number of lapses or omissions, that is, dots that they failed to respond to. For the 3 hour group [click], the number of lapses increased across the 7 days and did not return to baseline even after 3 nights of recovery. Even for the 5 and 7 hr groups, lapses increased and did not return to baseline after 3 nights of recovery. What do these result show? Seven days of sleep restriction degraded vigilance performance in a sleep-dose-dependent manner. With mild to moderate sleep restriction (7- and 5-h TIB), performance initially declined and, after a few days, appeared to stabilize at a lower-than-baseline level for the remainder of the sleep restriction period. With severe sleep restriction (3-h TIB), however, performance declined continuously across the sleep restriction period, with no apparent stabilization of performance. Increasing sleep to 9-h TIB for 3 nights did not bring performance back to baseline. Based on these findings, it appears that the inflection point (i.e. the minimum amount of nightly sleep required to achieve a state of equilibrium in which daytime alertness and performance can be maintained at a stable, although reduced, level) is approximately 4 h per night. Sleep durations that do not satisfy the core sleep requirement (of about 4 h) would, across days, result in continued reduction in alertness and performance; whereas sleep durations that satisfy the core requirement would produce deficits in alertness and performance relative to baseline, but this deficit would not continue across days indefinitely a stable level of reduced alertness and performance would eventually be achieved; and additional sleep (i.e. incremental increases in the duration of sleep beyond the core requirement) would produce correspondingly higher, and stable, levels of alertness and performance.

13 13 Restricted sleep also produces a decrease in physiological alertness, primarily in the right hemisphere. The decline is evident in frontal areas immediately [click], but posterior areas start to show a decline only after several days of sleep restriction [click]. These data suggest that the length or duration of continuous sleep restriction may be a more important indicator of the magnitude of deficits than the degree of sleep loss. In other words, the brain may be capable of adaptation or compensation for short periods even when the sleep loss is extreme (e.g., 24 h); however, the brain may not be adaptable when there is a chronic lack of sufficient sleep. These deficits are consistent with what has been seen following total sleep deprivation. The effects of sleep restriction can be quite subtle, yet this insidious level of sleepiness can lead to dangerous consequences. Cote, K., Milner, C., Osip, S., Baker, M., & Cuthbert, B. (2008). Physiological arousal and attention during a week of continuous sleep restriction. Physiology & Behavior, 95(3),

14 14 The P3, a neurophysiological measure of attention that we saw in the Masterclass on Exercise and Brain Health, declined steadily throughout the sleep restriction period, but recovered to baseline on sleep recovery. As sleep debt accumulates across days, performance becomes progressively worse over time; In one study, 14 days of chronic sleep restriction (4 or 6 h TIB each night, so not what we think of as unreasonably short) produced comparable cognitive deficits to those produced by h of total sleep deprivation. Research has also shown that the recovery rate from chronic sleep restriction may be slower than from acute total sleep loss. Due to circadian limitations on sleep duration, it is unlikely that we can recover from 5 days of chronic sleep restriction in one night of more than 10 h TIB; therefore, residual attentional deficits will still be noticeable after one night of recovery. Thus, attempting to recover lost sleep from a work week by extending sleep on a weekend night is likely insufficient for recuperating impaired alertness and sustained attention. Other studies examining recovery after chronic sleep restriction have found that PVT performance remains substandard even after 3, 5, or 7 recovery nights of 8 h TIB. However, napping prior to sleep deprivation can significantly improve reaction time performance and spending 10 h TIB daily for 1 week prior to experiencing chronic partial sleep restriction mitigated the decrease in PVT performance during sleep loss and facilitated improvement of PVT performance during recovery. Thus, chronic sleep restriction induces slow changes in neural processes mediating alertness and attention that cause performance to become progressively worse over time, producing the accumulation of severe performance decrements. Similarly, the slow recovery rate from chronic sleep restriction suggests that this type of sleep loss may induce long-term neuromodulatory changes in brain physiology.

15 The Neuroscience School 15 Sleep restriction affects mental flexibility, attention shifting, and the inhibition of automatic responses, all reflective of executive function. In 2010, Plessow and colleagues studied new parents. New parents are a population of healthy adults who are often subjected to chronic sleep restriction for several months due to nightly feedings and caring for a new infant. The researchers wanted to know whether their ability to flexibly adapt to changing environmental demands was impaired. They used a task-switching paradigm, in which the parents randomly switched between tasks on a cue. Sleepdeprived new parents showed significantly slower reaction times during task switches compared to new parents who reported adequate sleep. These results indicate that chronic sleep restriction can impair an individual s ability to implement task goals in order to switch tasks in a fast-changing environment factors especially important for doctors, pilots, and individuals in the armed forces, who constantly rely on fast and flexible goal shifting and are likely to experience chronic sleep restriction - but also for others who voluntarily restrict their sleep hoping to gaining more productive hours. PLESSOW, F., KIESEL, A., PETZOLD, A., & KIRSCHUM, C. (2011). Chronic sleep curtailment impairs the flexible implementation of task goals in new parents. Journal of Sleep Research, 20(2), doi: /j x

16 Sleep is governed by circadian rhythm Adults need 7-9 hrs sleep/night Trend is for less sleep - screen time Sleep enhances learning and memory Restricted sleep - reduced alertness A weekend is not enough to recover from restricted sleep during the week The Neuroscience School 16 To summarize so far: 1. Sleep is governed primarily by our our circadian rhythm, or biological clock. Over the course of a night, brain activity fluctuates between REM and NREM sleep. 2. The National Sleep Foundations recommends that adults get between 7 and 9 hours of sleep per night, yet surveys are showing that we are getting less sleep than we used to. A big contributor is screen time. 3. Sleep enhances learning and memory. A period of post-learning sleep enhances our ability to retain declarative information and improves performance in procedural skills. 4. Restricted sleep leads to reduced alertness and micro sleeps that can have devastating effects. 5. Chronic restricted sleep reduces our ability to sustain attention that does not return to baseline even after 3 nights of normal sleep. 6. Restricted sleep also produces a decrease in physiological alertness and attempting to recover lost sleep from a work week by extending sleep on a weekend is likely insufficient for recuperating impaired alertness and sustained attention.