Chapter 8: Wakefulness and Sleep PDF

G R O U P 1 P R E S E N T A T I O N C H A P T E R 8 Wakefulness and Sleep D E C E M B E R 2 0 , 2 0 2 4  MODULE 8.1 RHYTHMS OF WALKI...

G R O U P 1 P R E S E N T A T I O N C H A P T E R 8 Wakefulness and Sleep D E C E M B E R 2 0 , 2 0 2 4  MODULE 8.1 RHYTHMS OF WALKING AND SLEEPING Endogenous Rhythms Endogenous rhythms refer to biological cycles that are generated from within an organism, rather than being solely influenced by external environmental factors. These rhythms include: Endogenous Circadian Rhythms - These are daily cycles that last about 24 hours, regulating various physiological processes such as sleep-wake cycles, alertness, and hormonal changes. For example, even if a person stays awake all night, they will typically feel more alert in the morning due to their circadian rhythm. Endogenous Circannual Rhythms - These are yearly cycles that help organisms anticipate seasonal changes. For instance, migratory birds exhibit an endogenous circannual rhythm that prompts them to migrate at the appropriate times, even in stable environments where they lack seasonal cues.  Mechanisms of the Biological Clock Curt Richter (1967) introduced the concept that the brain generates its own rhythms called a “biological clock” and he reported that the biological clock is insensitive to most forms of interference. Blind or deaf animals generate circadian rhythms, although they slowly drift out of phase with the external world. The circadian rhythm remains surprisingly steady despite food or water deprivation, X-rays, tranquilizers, alcohol, anesthesia, lack of oxygen, most kinds of brain damage, or the removal of endocrine organs. Even an hour or more of induced hibernation often fails to reset the biological clock. Age differences in circadian rhythms  Suprachiasmatic Nucleus (SCN) Although cells throughout the body generate circadian rhythms, the main driver of rhythms for sleep and body temperature is the suprachiasmatic (soo-pruh-kie-as-MAT-ik) nucleus, or SCN, a part of the hypothalamus. It gets its name from its location just above (“supra”) the optic chiasm. The SCN generates circadian rhythms itself in a genetically controlled manner. If SCN neurons are disconnected from the rest of the brain or removed from the body and maintained in tissue culture, they continue to produce a circadian rhythm of action potentials. Even a single isolated SCN cell can maintain a circadian rhythm, although interactions among cells sharpen the accuracy of the rhythm. Biochemistry of Circadian rhythm The suprachiasmatic nucleus produces the circadian rhythm, but how? Research on production of the circadian rhythm began with insects. Studies on the fruit fly Drosophila found several genes responsible for a circadian rhythm. Two of these genes, known as period (abbreviated PER) and timeless (TIM), produce the proteins PER and TIM. The concentration of these two proteins, which promote sleep and inactivity oscillates over a day, based on feedback interactions among neurons.,  Melatonin The pineal gland releases the hormone melatonin. Melatonin is a widespread chemical, found in nearly all animals as well as in plants and bacteria. In all cases, it is released mostly at night. In diurnal animals like humans, it increases sleepiness. In nocturnal animals, it increases wakefulness. People who have pineal gland tumors sometimes stay awake for days at a time. In addition to regulating sleep and wakefulness, melatonin also helps control the onset of puberty and bodily adjustments to changes of season (such as hibernation). Melatonin secretion starts to increase about 2 or 3 hours before bedtime. Taking a melatonin pill in the evening has little effect on sleepiness because the pineal gland produces melatonin at that time anyway. However, people who take melatonin earlier start to become sleepy. In the process, it shifts the circadian rhythm such that the person starts to become sleepy earlier than usual the next day also. Melatonin pills are sometimes helpful for people who travel across time zones and need to sleep at an unaccustomed time.  MODULE 8.2 STAGES OF SLEEP AND BRAIN MECHANISMS  Sleep WHAT IS SLEEP ? Sleep is a natural state where the brain actively reduces its activity and responsiveness to the environment. It is not just a passive state; rather, it serves important functions for our health, such as restoration and memory processing.  Other Interruptions of Conciousness Coma - In contrast to sleep, a coma is an extended period of unconsciousness caused by factors like head trauma or disease. Individuals in a coma exhibit low brain activity and minimal response to stimuli, and they cannot be easily awakened. Vegetative State - This state involves alternating periods of sleep and moderate arousal, but individuals do not show awareness of their surroundings or purposeful behavior. They may respond to painful stimuli with autonomic responses, but they lack conscious awareness. Sleep and Other Interruptions of Conciousness Minimally Conscious State - This is a higher level of consciousness than a vegetative state, where individuals may exhibit brief periods of purposeful actions and limited speech comprehension. Brain Death - This condition is defined by the absence of brain activity and response to any stimuli. It is typically confirmed after a person shows no signs of brain activity for 24 hours. The Stages of Sleep Stage 1 Sleep - This is the lightest stage of sleep, where the EEG shows irregular, jagged, low-voltage waves. Brain activity is less than in relaxed wakefulness but higher than in deeper sleep stages. This stage is a transition between wakefulness and sleep. Stage 2 Sleep - Characterized by the presence of sleep spindles (bursts of 12- to 14-Hz waves) and K-complexes (sharp waves). This stage involves temporary inhibition of neuronal firing and is considered a deeper sleep than Stage 1. Stage 3 Sleep - This stage features slow-wave sleep, where the EEG shows large, slow waves. Heart rate, breathing rate, and brain activity decrease, indicating a deeper level of sleep. Neuronal activity is highly synchronized during this stage. The Stages of Sleep Stage 4 Sleep - Often combined with Stage 3 in modern classifications, this stage also exhibits slow-wave activity but with a higher proportion of slow waves compared to Stage 3. It represents the deepest level of sleep. REM Sleep (Rapid Eye Movement Sleep) - Also known as paradoxical sleep, this stage is characterized by high brain activity similar to wakefulness, but with relaxed neck muscles. It is during REM sleep that most dreaming occurs, and it plays a crucial role in memory consolidation. Michel Jouvet Paradoxical Experiment: Jouvet was studying the effects of removing the cerebral cortex on cats. or REM Sleep Observation: During periods of apparent sleep, the cats exhibited high brain activity but complete muscle relaxation. Discovery of Jouvet (1960) then recorded the same phenomenon in normal, intact cats and named it REM paradoxical sleep because it is deep sleep in some ways and light in others. (The term paradoxical means “apparently self-contradictory.”)  Nathaniel Kleitman and Eugene Aserinsky Paradoxical or REM Sleep Eye Movement Observation: They noticed rapid eye movements during sleep, a phenomenon previously overlooked. REM Sleep: They named this phase "rapid eye movement (REM) sleep." Synonymy: They later realized that REM sleep is equivalent to Jouvet's paradoxical sleep.. Researchers use the term REM sleep when referring to humans but often prefer the term paradoxical sleep for species that lack eye movements. The stages other than REM are known as non- REM (NREM) sleep CHARACTERISTICS OF REM REM sleep combines aspects of both deep and light Paradoxical sleep. the brain is highly active, similar to a waking state. or REM Sleep The body is paralyzed, preventing physical action. Heart rate, blood pressure, and breathing rate fluctuate. -associated with erections in males and vaginal moistening in females The entire sleep cycle, from light sleep to deep sleep and back to light sleep and REM, typically lasts around 90 minutes. In short, REM sleep combines aspects of deep sleep, light sleep, and features that are difficult to classify as deep or light. The pattern of sleep stages varies as a Paradoxical or REM Sleep function of age, health, and other factors The frequency of awakenings correlates with loss of cells in the hypothalamus, and with a tendency toward cognitive decline (Blackwell et al., 2014; Lim et al., 2014). REM is not the same thing as dreaming. REM becomes most common toward the end of the night’s increases. 1. Brain Activity in REM Sleep  Brain Activity in REM Sleep Researchers interested in the mechanisms of REM decided to use a PET scan to determine which brain areas increased or decreased their activity during REM. Although that research might sound simple, PET requires injecting a radioactive chemical. Imagine trying to give sleepers an injection without awakening them. Further, a PET scan yields a clear image only if the head remains motionless during data collection. If the person tosses or turns even slightly, the blurry image is worthless. To overcome these difficulties, researchers in two studies persuaded young people to sleep with their heads firmly attached to masks that did not permit any movement. They also inserted a cannula (plastic tube) into each person's arm so that they could inject radioactive chemicals at various times during the night. So imagine yourself in that setup. You have a cannula in your arm and your head is locked into position.  Brain Activity in REM Sleep Now try to sleep. Because the researchers foresaw the difficulty of sleeping under these conditions (i), they had their participants stay awake the entire previous night. Someone who is tired enough can sleep even under trying circumstances. (Maybe.) Now that you appreciate the heroic nature of the pro-cedures, here are the results: During REM sleep, activity increased in the pons (which triggers the onset of REM sleep) and the limbic system (which is important for emotional re-sponses). Activity decreased in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex but increased in parts of the parietal and temporal cortex (Braun et al., 1998; Maquet et al., 1996). REM sleep is associated with a distinctive pattern of high-amplitude electrical potentials known as PGO waves, for pons-geniculate-occipital (see Figure 8.16). Waves of neural activity are detected first in the pons, shortly afterward in the lateral geniculate nucleus of the thalamus, and then in the occipital cortex (Brooks & Bizzi,963; Laurent, Cespuglio, & Jouvet, 1974). A path of axons from the ventral medulla releasing GABA promotes REM sleep. Exciting or inhibiting these axons can initiate or stop REM. Apparently these axons initiate REM by inhibiting other inhibitory neurons—a case of excitation by a double negative (Weber et al., 2015). Several other transmitters also influence REM. Injections of the drug carba-chol, which stimulates acetylcholine synapses, quickly move a sleeper into REM sleep (Baghdoyan, Spotts, & Snyder, 1993). Note that acetylcholine is important for both wakefulness and REM sleep, states of brain arousal. Serotonin and norepinephrine interrupt REM sleep (Boutrel, Franc, Hen, Hamon, & Adrien, 1999; Singh & Mallick, 1996). Sleep Sleep needs vary genetically, with most adults Disorders needing 7.5 to 8 hours per night, though some can function well on just 3 hours. Research on mice with a mutant gene shows that increased sleep needs lead to similar negative effects when deprived as in normal mice. Feeling tired during the day indicates inadequate sleep, which impairs memory, attention, cognition, and emotional regulation, and raises the risk of depression. PGO waves are brain signals seen during REM sleep (Rapid Eye Movement sleep). They start in the pons (brainstem), go to the geniculate nucleus (thalamus), and finally reach the occipital cortex (visual area). These waves are synchronized with eye movements during REM sleep. Sleep Disorders INSOMNIA Insomnia is the inability to fall asleep or stay asleep, leading to poor sleep quality. Factors like noise, stress, physical discomfort, and medical conditions such as epilepsy, depression, or food intolerances can disrupt sleep. Worrying about morning routines or other stressors can contribute to difficulty sleeping. Phase-delayed rhythms make it hard to fall asleep, while phase-advanced rhythms cause early awakenings. Understanding the root cause is key to effective treatment. Sleep Disorders SLEEP APNEA Sleep apnea is a condition where breathing is impaired during sleep, causing frequent awakenings and leading to daytime sleepiness, impaired attention, and increased risk of stroke and heart problems. Sleep apnea is associated with neuron loss and deficiencies in learning, reasoning, attention, and impulse control, likely caused by repeated periods of low oxygen during sleep. Contributing factors include genetics, hormonal changes, age-related brain deterioration, obesity (particularly in middle-aged men), and narrower airways. Recommended approaches include weight loss, avoiding alcohol and tranquilizers, using CPAP (continuous positive airway pressure) devices, and in some cases, surgery to open breathing spaces or adjust the jawbone.  A continuous positive airway pressure (CPAP) mask The mask fits snugly over the nose and delivers air at a fixed pressure, strong enough to keep the breathing passages open. Sleep Disorders NARCOLEPSY Affecting 1 in 1,000 people, is marked by daytime sleepiness and can include cataplexy (muscle weakness triggered by emotions), sleep paralysis, and hypnagogic hallucinations— REM-like states intruding into wakefulness. It is linked to the loss of hypothalamic cells producing orexin, a neurotransmitter critical for maintaining wakefulness. This loss is likely due to an autoimmune reaction. Dogs and mice lacking orexin or its receptors exhibit similar symptoms, highlighting its role in the disorder. While no orexin-specific drugs exist, stimulant medications like methylphenidate (Ritalin) are commonly used to manage symptoms by enhancing dopamine and norepinephrine activity. Sleep Disorders PERIODIC LIMB MOVEMENT DISORDER Involves repeated, involuntary leg (and sometimes arm) movements during sleep, distinct from restless leg syndrome, which occurs while awake. Movements often occur every 20 to 30 seconds, lasting for minutes or hours, primarily during NREM sleep. This disorder is more common in middle-aged and older individuals and is problematic only when movements are persistent and disruptive. Occasional involuntary leg kicks, especially when falling asleep, are normal and not considered part of the disorder. Sleep Disorders REM BEHAVIOR DISORDER Involves vigorous physical movements during REM sleep, as if acting out dreams, due to a lack of normal muscle relaxation. Individuals often dream of defending themselves, leading to actions like punching, kicking, or leaping, which may result in injuries or property damage. Research in mice suggests the disorder may stem from inadequate inhibitory neurotransmission, particularly involving GABA and related neurotransmitters. Mice with deficient inhibitory transmission exhibit movements during REM sleep similar to those observed in humans with the disorder. Sleep Disorders NIGHT TERRORS, SLEEPWALKING, AND SEXSOMNIA Night Terrors: Intense episodes of anxiety during NREM sleep, often causing screaming awakenings, are more severe than nightmares and typically involve simple or no dream content, primarily affecting children. Sleepwalking: Common in children and often linked to other sleep difficulties like snoring or night terrors, sleepwalking occurs during slow-wave sleep, with actions that are poorly planned, sometimes dangerous, and rarely remembered. Sexsomnia: A sleep disorder where individuals engage in sexual behavior during sleep, often without recollection, potentially linked to sleepwalking or sleep apnea, and exacerbated by stress, medication, or unusual sleep conditions.  MODULE 8.3 WHY SLEEP? WHY REM? WHY DREAMS?  Functions of Sleep Sleep has many functions: - Resting muscles and conserving energy. - Supporting neuron repair and synapse reorganization (Vladyslav & Harris, 2013). - Strengthening memories. Lack of sleep can make you more stressed, worsen mental health, and impair performance (Minkel et al., 2012; van der Kloet et al., 2012). Sleep deprivation is as dangerous as drunk driving (Falleti et al., 2003) and even activates your immune system, mimicking illness (Matsumoto et al., 2001).  Sleep and Energy Conservation Sleep likely began with a simple function, to which evolution added more over time. Even bacteria, which lack a nervous system, follow cycles of activity and inactivity (Mihalcescu et al., 2004). A key hypothesis is that sleep's original purpose was to conserve energy (Kleitman, 1963; Siegel, 2009, 2012)Sleep functions similarly to hibernation, which is essential for survival during scarce food availability. Animals deprived of hibernation become as disturbed as humans deprived of sleep. Both processes help conserve energy in challenging conditions..  Hibernation: A Sleep-Like State Hibernation is similar to sleep but much deeper. Animals lower their body temperature close to the environment (but not enough for blood to freeze), drastically reduce heart rate, and shrink neuron cell bodies, with synapses disappearing and regenerating later (Peretti et al., 2015). Here are some interesting facts about hibernation: 1. Bears and Hibernation: Bears "hibernate" by sleeping most of the winter, slightly lowering their body temperature and slowing their metabolism. However, their state is less extreme than that of smaller animals like bats or squirrels (Tøien et al., 2011). 2. Hamsters Hibernate Too: Hamsters hibernate in cool, dim places during winter. If your hamster seems dead, check if it's just hibernating before assuming the worst..  Hibernation: A Sleep-Like State 3. Reptiles and Amphibians: Many reptiles and amphibians enter a hibernation-like state during winter, slowing metabolism and staying dormant until spring (Sanders et al., 2015). 4. Brief Waking Periods: Hibernating animals wake up every few days or weeks for a few hours. During these times, they mostly sleep (Barnes, 1996; Williams et al., 2012). 5. Hibernation and Longevity: Hibernation slows aging. Hamsters and fat-tailed dwarf lemurs that hibernate live significantly longer than non-hibernating relatives (Lyman et al., 1981; Blanco & Zehr, 2015). Hibernation also reduces vulnerability to infection and trauma, making procedures like brain injections less harmful during this state (Zhou et al., 2001).  Species Differences in Sleep Sleep patterns vary widely across species, depending on their environment and needs. Some species sleep much less or adapt their sleep to unique circumstances: 1. Cavefish: Mexican cavefish living in lightless caves sleep only 2–4 hours per day, unlike their surface-dwelling relatives, who sleep over 13 hours daily (Duboué et al., 2011, 2016). 2. Polar Animals: Near the poles, animals like sandpipers and reindeer reduce sleep during constant daylight in summer. Male sandpipers stay active for up to 23 hours a day while competing for mates, with no apparent harm (Lesku et al., 2012).  Species Differences in Sleep 3. Aquatic Mammals: Dolphins, whales, and seals can sleep with one brain hemisphere at a time, allowing them to surface for air or stay alert while swimming. After giving birth, dolphins and their calves stay awake for weeks without adverse effects (Rattenborg et al., 2000; Lyamin et al., 2005). 4. Swifts: Young European swifts can stay airborne for up to two years, gliding at night and possibly sleeping mid-flight. Their exact sleep patterns are unclear due to difficulty in measuring their brain activity (Bäckman & Alerstam, 2001). 5. Frigate Birds: Great frigate birds fly for weeks over the ocean, sleeping less than 45 minutes per night in short bursts, often with one brain hemisphere. On land, they sleep over 12 hours daily, showing how sleep adapts to environmental demands (Rattenborg et al., 2016).  Species Differences in Sleep - During migration, birds drastically reduce sleep, resting only about a third of their usual amount. They take brief daytime naps (less than 30 seconds) to compensate and still perform well on tasks. - Outside migration, the same birds perform poorly when sleep-deprived (Rattenborg et al., 2004; Fuchs et al., 2006). - How birds and other animals like dolphins or frigate birds temporarily lower their sleep needs remains unknown. This supports the idea that sleep primarily conserves energy rather than fulfilling an irreplaceable function. Sleep Pattern Across Species Animals' sleep habits align with their survival needs: Grazing Animals: Spend most of their time eating and sleep less. Carnivores: Eat quickly and sleep more. Prey and Predators: Prey animals sleep less to stay alert, while predators sleep more securely. Insect-Eating Bats: Feed during the evening when insects are active, then sleep the rest of the day.  Sleep and Memory Sleep is essential for improving memory and learning, as it helps solidify memories and uncover hidden insights. Sleep aids in creative problem-solving, particularly during REM sleep. The brain replays learning patterns during sleep, particularly in the hippocampus, forming new neural connections that strengthen memories. Sleep also helps clean up the brain by weakening less useful connections, enhancing the important ones formed during wakefulness. Functions of REM Sleep  Functions of REM Sleep An average person spends about a third of his or her life asleep and about a fifth of sleep in REM, totaling about 600 hours of REM per year. Presumably, REM serves a biological function. But what is it? One way to approach this question is to compare the people or animals with more REM to those with less. REM sleep is widespread in mammals and birds, indicating that it is part of our ancient evolutionary heritage. Some species, however, have far more than others. As a rule, the species with the most total sleep hours also have the highest percentage of REM sleep (Siegel, 1995). Cats spend up to 16 hours a day sleeping, much or most of it in REM sleep. Rabbits, guinea pigs, and sheep sleep less and spend little time in REM. Functions of REM Sleep Figure 8.20 illustrates the relationship between age and REM sleep for humans. The trend is the same for other mammalian species. Infants get more REM and more total sleep than adults do, confirming the pattern that more total sleep predicts a higher percentage of REM sleep. Among adult hu-mans, those who sleep 9 or more hours per night have the highest percentage of REM sleep, and those who sleep 5 or fewer hours have the least percentage. This pattern implies that although REM is no doubt important, NREM is more tightly regulated. The amount of NREM varies less among individuals and among species. One hypothesis is that REM is important for strengthening memory (Crick & Mitchison, 1983). Although memory consolidation does occur during REM, many people take antidepressant drugs that severely decrease REM sleep but cause no memory problems (Rasch, Pommer, Diekelmann, & Born, 2009). Research on laboratory animals indicates that antidepressant drugs sometimes even enhance memory (Parent, Habib, & Baker, 1999).  Functions of REM Sleep Another hypothesis sounds odd because we tend to imagine a glamorous role for REM sleep: David Maurice (1998) proposed that REM just shakes the eyeballs back and forth enough to get sufficient oxygen to the corneas of the eyes. The corneas, unlike the rest of the body, get oxygen directly from the surrounding air. During sleep, because they are shielded from the air, they deteriorate slightly (Hoffmann & Curio, 2003). They do get some oxygen from the fluid behind them (see Figure 5.1), but when the eyes are motionless, that fluid becomes stagnant. Moving the eyes increases the oxygen supply to the corneas. According to this view, REM is a way of arousing a sleeper just enough to shake the eyes back and forth, and the other manifestations of REM are just by- products. This idea makes sense of the fact that REM occurs mostly toward the end of the night's sleep, when the fluid behind the eyes would be the most stagnant. It also makes sense of the fact that individuals who spend more hours asleep devote a greater percentage of sleep to REM. (If you don't sleep long, you have less need to shake up the stagnant fluid.) However, as mentioned, many people take antidepressants that restrict REM sleep. They are not known to suffer damage to the cornea. Biological Perspective on Dreaming Dream research faces a special problem: All we know about dreams comes from people's self-reports, and researchers have no way to check the accuracy of those reports. In fact, we forget most dreams, and even when we do remember them, the details fade quickly.  Biological Perspective on Dreaming Biological Perspective on Dreaming The Activation-Synthesis Hypothesis According to the activation-synthesis hypothesis, a dream represents the brain's effort to make sense of sparse and distorted information. Dreams begin with periodic bursts of spontaneous activity in the pons— the PGO waves previously described —that activate some parts of the cortex but not others. The cortex combines this haphazard input with whatever other activity was already occurring and does its best to synthesize a story that makes sense of the information (Hobson & McCarley, 1977; Hobson, Pace-Schott, & Stickgold, 2000; McCarley & Hoffman, 1981). Consider how this theory handles a couple of common dreams. Most people have had occasional dreams of falling or flying. While you are asleep, you lie flat, unlike your posture for the rest of the day. Your brain in its partly aroused condition feels the vestibular sensation of your position and interprets it as flying or falling. Have you ever dreamed that you were trying to move but couldn't? Most people have. An interpretation based on the activation- synthesis theory is that during REM sleep (which accompanies most dreams), your motor cortex is inactive and your major postural muscles are virtually paralyzed. Biological Perspective on Dreaming That is, when you are dreaming, you really cannot move, you feel your lack of movement, and thus, you dream of failing to move. One criticism is that the theory's predictions are vague. If we dream about falling because of the vestibular sensations from lying down, why don't we always dream of falling? If we dream we cannot move because our muscles are paralyzed during REM sleep, why don't we always dream of being paralyzed? Furthermore, most dreams have no apparent connection to any current stimuli (Foulkes & Domhoff, 2014; Nir & Tononi, 2010).dream, and sudden scene changes are common. We also lose a sense of volition-that is, planning (Hobson, 2009). It seems that events just happen, without any intention on our part. Meanwhile, activity is relatively high in the inferior (lower) part of the parietal cortex, an area important for visuo-spatial perception. Patients with damage here fail to bind body sensations with vision. They also report no dreams. Fairly high activity is also found in the areas of visual cortex other than the primary visual cortex. Those areas are presumably important for the visual imagery that accompanies most dreams. Finally, activity is high in the hypothalamus, amygdala, and other areas important for emotions and motivations (Gvilia, Turner, McGinty, & Szymusiak, 2006). the idea is that either internal or external stimulation activates parts of the parietal, occipital, and temporal cortex. 'The arousal develops into a hallucinatory perception, with no sensory input from area Vl to override it. This idea, like the activation-synthesis hypothesis, is hard to test because it does not make specific predictions about who will have what dream and when. G R O U P 1 P R E S E N T A T I O N Thank you D E C E M B E R 2 0 , 2 0 2 4