Sleep & Dreams

1. Sleep & Dreams • Circadian Rhythm: Attention and memory peak in a cyclic fashion over a 25-hour cycle. About age 20 (later for women) we move from being night-loving owls to morning-loving larks (Roenneberg et al., 2004).There is a cost: Larks do better in school, take more initiatives, and are less vulnerable to depression. (Randler, 2009).Sleep isn't just one thing. There are four distinct sleep stages. One of the most important in terms of evolutionary psychology is Rapid Eye Movement (REM) sleep.Discovered by Aserinsky in 1952. Birds and mammals exhibit REM sleep; reptiles and amphibians do not.

2. Sleep & Dreams • Memorize Fig 8.2!  We begin in Waking Beta, move into Waking Alpha (think of late-night infomercials when you're too tired to change the channel),  go to REM sleep, then into NREM-1 (hallucinations of floating, alien abductions, etc.), then to NREM-2, finally to true deep sleep NREM-3.Children wet the bed in NREM-3. Sleepwalking and sleeptalking also occurs in NREM-3. • REM has a strong biological/evolutionary dimension not well understood. Many men trouble with erectile dysfunction have sleep-related erections.The motor cortex is active during REM sleep, but the brainstem blocks the messages. This immobility may linger as  you awaken from REM, creating sleep paralysis.Internally active, yet externally immobilized.

3. Sleep & Dreams • The sleep cycle repeats itself every 90 minutes or so.During the night, NREM-3 grows shorter.REM and NREM-2 periods grow longer.By morning we have dreamt for 100 minutes in REM.37% of people report rarely or never having dreams that they can remember the next morning.Yet even they more than 80% of the time recall a dream after being awakend (Moore, 2004). • We sleep about 600 hours a year, with 1500 dreams yearly, or 100,000 over a typical lifetime. REM protective paralysis and REM sleep itself must have profound benefits.

4. Sleep & Dreams • The Biological Clock (Fig. 8.5): Light striking the retina signals the suprachiasmatic nucleus (located in the hypothalamus) to suppress the pineal gland's production of the sleep hormone called melatonin. At night, the SCN quiets down, allowing the pineal gland to release melatonin into the bloodstream.Sleep patterns have a strong genetic influence (Hor & Tafti, 2009).Artificial light delays sleep (Cziesler et al. 1999).

5. Why Do We Sleep? • Sleep patterns fill an ecological niche; we were daylight and dusk hunter-gatherers.Sleep restores and repairs brain tissue. Free radicals are toxic to neurons. Sleeps prunes unused connections, which explains why newborns sleep the most; their brains are constantly being re-organized. (Gilestro, 2009)Sleep consolidates memories, but strengthening and stabilizing neural memory traces. • People trained to perform a task recall it better after a night's sleep, better than after several hours awake.After sleeping well, seniors remember more.Neural activity during slow-wave sleep re-enacts and promotes recall of prior novel experiences.Deep sleep releases pituitary growth hormone

6. Sleep Disorders • The brain keeps an accurate account of sleep debt for at least two weeks.REM and NREM-2 sleep occur mostly in the final hours of the night, and help strengthen the neural connections that produce 'muscle memory'.Sleep loss is a predictor of depression. Young people who slept 5 hours or less a night had a 71% higher risk of depression. (Gangswisch, 2010).Try the Table 8.1 test (Maas, 1999) yourself.Sleep deprivation increases ghrelin, a hunger-arousing hormone, and decreases the appetite-suppressing hormone leptin.It increases cortisol, a stress hormone that stimulates the body to make fat. (Chen, 2008)

7. Sleep Disorders • Sleep deprivation can suppress immune cell reaction. Cohen et al. 2009: Volunteers (-7 hrs sleep), infected with a cold virus, were 3 times more likely to develop a cold  than those of +8 hrs. Sleep deprivation slows reaction time and increase errors on visual attention tasks (Lim & Donges, 2010)Canadian traffic accidents, Fig. 8.7How sleep deprivation affects us: Fig. 8.8

8. Sleep Disorders • Insomnia is defined as persistent problems in falling or staying asleep (Irwin et al., 2006)Insomnia sufferers typically overestimate how long it takes them to fall asleep.They underestimate how long they have actually slept.Narcolepsy is a sudden attack of sleepiness, lasting about five minutes.A narcoleptic may collapse directly in REM sleep, with a loss of muscular tension.Taheri et al. 2002: There can be a relative absence of a hypothalamic neural centre that produces orexin (hypocretin), a neurotransmitter linked to alertness.

9. Sleep Disorders • Sleep apnea: a condition where the sufferer intermittently stops breathing during sleep. After an airless minute, blood oxygen deprivation arouses them, and they wake up to snort air.They are deprived of slow-wave NREM-3 sleep.Sleep apnea is correlated to (but not caused by) obesity.Night terror occur during the first few hours of NREM-3 sleep, doubling heart and breathing rates.

10. Dreams • REM dreams are hallucinations of the sleeping mind: vivid, emotional, and bizarre. 8 in 10 dreams are marked by at least one negative event or emotion (Domhoff, 2007).Only 1 in 10 dreams and 1 in 30 dreams have sexual content for young men and young women.More commonly, dreams incorporate traces of the previous day's non-sexual experiences and preoccupations.We still monitor the environment while we sleep. Sensory stimuli--a particular odor or a phone's ringing--may be instantly and ingeniously woven into the dream story. Dement & Wolpert, 1958.We do not remember recorded information when asleep.

11. Why Do We Dream? • Freud: wish fulfilment in dreams' manifest content vs. latent content.To file away memories. People who hear unusual phrases or learn to find hidden visual images before bedtime remember less the next morning if awakened every time they begin REM sleep that if awakened during other sleep stages. (Karni & Sagi, 1994).To develop and preserve neural pathways.  Fig. 8.9Hobson, 1977: To make sense of neural static. A standing theory is that dreams erupt from neural activation spreading upward from the brainstem. Dreams are the brains (cerebral hemispheres') attempt to make sense of it.Limbic systems are highly active, while frontal lobes are not.

12. Why Do We Dream? • To reflect cognitive development. Domhoff, 2010: As children grow, dreams overlap with waking cognition and feature coherent speech. Dreams engage neural networks that are also active during daydreaming. Table 8.3 will be on the next exam.REM sleep rebound: Deprived of REM sleep, people will return morequickly to it when falling back into sleep. When finally allowed to sleep undisturbed, they literally sleep like babies.Withdrawing REM-suppressing sleep medications also increases REM sleep, but brings on nightmares.Mammals and birds, but not fish and reptiles, have REM sleep; the former havebrains that grow and learn after birth.