* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Bio Chap 15 - mlfarrispsych
Neuroanatomy wikipedia , lookup
State-dependent memory wikipedia , lookup
Types of artificial neural networks wikipedia , lookup
Lunar effect wikipedia , lookup
Nervous system network models wikipedia , lookup
Time perception wikipedia , lookup
Recurrent neural network wikipedia , lookup
Artificial general intelligence wikipedia , lookup
Emotion and memory wikipedia , lookup
Neuroesthetics wikipedia , lookup
Memory consolidation wikipedia , lookup
Neuroscience in space wikipedia , lookup
Brain Rules wikipedia , lookup
Circadian rhythm wikipedia , lookup
Optogenetics wikipedia , lookup
Biology of depression wikipedia , lookup
Neural oscillation wikipedia , lookup
Neuroeconomics wikipedia , lookup
Dual consciousness wikipedia , lookup
Neural engineering wikipedia , lookup
Consciousness wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Development of the nervous system wikipedia , lookup
Hard problem of consciousness wikipedia , lookup
Philosophy of experience wikipedia , lookup
Animal consciousness wikipedia , lookup
Metastability in the brain wikipedia , lookup
Artificial consciousness wikipedia , lookup
Delayed sleep phase disorder wikipedia , lookup
Sleep apnea wikipedia , lookup
Neuroscience of sleep wikipedia , lookup
Sleep paralysis wikipedia , lookup
Obstructive sleep apnea wikipedia , lookup
Sleep and memory wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Sleep deprivation wikipedia , lookup
Sleep medicine wikipedia , lookup
Rapid eye movement sleep wikipedia , lookup
Effects of sleep deprivation on cognitive performance wikipedia , lookup
Start School Later movement wikipedia , lookup
SLEEP AND CONSCIOUSNESS CHAPTER 15 Sleep and dreaming The neural basis of consciousness Sleep and Dreaming • The Function of Sleep – The fact that species with higher metabolic rates typically spend more time in sleep supports the hypothesis that sleep is restorative. – The Adaptive Hypothesis. • The amount of sleep an animal engages in depends on the availability of food and on safety considerations. • For example, predators (lions) and animals that can hide (bats) sleep a lot. • Vulnerable animals without shelter (cattle) and those that need to spend hours feeding (elephants) sleep very little. Time Spent in Sleep for Different Species Figure 15.1 Sleep and Dreaming Performance deficits show the importance of sleep. – Deprivation Studies • Performance declines in shift workers. • In long-term deprivation studies, performance declines at night and recovers somewhat during the day. – Night-Time Accidents • Driving accidents peak at 2 a.m • The Chernobyl meltdown, the Bhopal chemical plant leakage, and the Exxon Valdez oil spill occurred in the early morning hours. – Traveling eastward across time zones decreases performance. • For example, west coast teams playing in the east won fewer games than east coast teams playing in the west. Sleep and Dreaming • A circadian rhythm is a rhythm that is about a day in length. – The main biological clock in mammals is the suprachiasmatic nucleus (SCN) of the hypothalamus. • Lesioning the SCN in rats abolishes the normal 24hour rhythms of sleep, activity, body temperature, drinking, and steroid secretion. • The SCN is entrained to the day-night cycle by zeitgebers (“time-givers”); the most important zeitgeber is light. ◊ The Suprachiasmatic Nucleus Figure 15.2 (a) In the rat, the SCN is active during lights-on (its sleep period), but (b) not during darkness. Sleep and Dreaming • In isolation studies, subjects typically follow a longer sleep-wake cycle. – For example, Greenpeace volunteers living in isolation during the 4 months of darkness of the Antarctic winter had a sleep/wake cycle of approximately 25 hours. – Some researchers believe the clock is linked to the 24.8-hour lunar cycle. – But subject control of room lighting may create an artifact. • Bright light at the end of the day lengthens the cycle. • When light was kept too dim to influence the cycle, the sleepwake period averaged 24.18 hours. Sleep & Wake Periods During Isolation Figure 15.3 Sleep and Dreaming The SCN regulates the pineal gland’s secretion of melatonin, a hormone that induces sleepiness. Melatonin is often used to combat jet lag and to treat insomnia in shift workers and in the blind. Light resets the clock by suppressing melatonin secretion. Light information reaches the SCN by way of the retinohypothalamic pathway. Ganglion cells in the retina contain melanopsin, which is a lightsensitive substance, or photopigment. This system explains why some blind individuals entrain to light. Melanopsin in Ganglion Cells Figure 15.4 The cells were labeled with a fluorescent substance that reacts to melanopsin. Sleep and Dreaming • Ultradian rhythms are those that are shorter than a day in length. – Hormone production, urinary output, alertness, and other functions follow regular cycles throughout the day. – One example of an ultradian rhythm is the basic rest and activity cycle, which is a rhythm that is about 90-100 minutes long. – Alertness, daydreaming, and EEG activity follow this cycle. – This cycle also extends into sleep, with 90-minute variations in arousal. ◊ Sleep and Dreaming The most important measure of sleep activity is the electroencephalogram, or EEG. When a person is awake, the EEG is a mix of alpha (8-12 Hz) and beta (13-30 Hz) waves. As the person slips into the light first stage of sleep, the EEG shifts to theta (4-7 Hz) waves. – About 10 minutes later Stage 2 begins, indicated by: • sleep spindles, brief bursts of 12- to 14-Hz waves; • K complexes, sharp, high amplitude waves that occur once a minute. Stages 3 and 4 are known as slow wave sleep and are characterized by large, slow delta waves at a frequency of 1-3 Hz. EEG and the Stages of Sleep Figure 15.5 Sleep and Dreaming • After stage 4 the sleeper moves rather quickly back through the stages in reverse order. • But rather than returning to Stage 1, the sleeper enters REM sleep. – REM, or rapid eye movement sleep is so called because the eyes dart back and forth horizontally during this stage. – REM sleep increases over the night and deep slow wave sleep decreases. – Most dreaming occurs during REM sleep. – Non-REM dreams are described by subjects as “thinking” and are less vivid and less hallucinatory. Time Spent in Various Sleep Stages Figure 15.6 Sleep and Dreaming Activation-Synthesis Hypothesis Dreams are a by-product that results when the brain uses information from memory to make sense of random neural activity generated by the brain stem. One hypothesis of REM sleep function is that it promotes neural development during childhood. REM sleep makes up 50% of sleep during infancy and decreases until adolescence, when it reaches adult levels Excitation that spreads through the brain from the pons during REM sleep encourages differentiation, maturation, and myelination in higher brain centers. Sleep and Dreaming REM Sleep and Memory REM sleep increases following learning, and REM deprivation after learning reduces retention. The amount of REM sleep corresponds to the quality of learning. Replay of activity that occurred during learning is synchronized with theta activity in the hippocampus. After 4-7 days—the time required for memories to become independent of the hippocampus—replay shifts out of phase with theta. This may be a period of memory erasure. (Remember that out-ofphase stimulation produces long-term depression.) According to the reverse learning hypothesis, the brain achieves efficiency by purging memories during REM sleep. Sleep and Dreaming • Non-REM Sleep and Memory – Enhancing slow potentials (using TMS) improved recall of word associations learned before sleep. – According to Ribeiro, non-REM sleep is a period of recall (replay) and REM sleep is a period of consolidation. – A 60-90 minute nap containing both REM and non-REM sleep produces significant improvement in learned performance. – Overnight improvement on a learning task was correlated with the percentage of slow-wave sleep during the first quarter of the night and the percentage of REM sleep during the final quarter. Sleep and Dreaming • Sleep Controls – Adenosine accumulates during waking in the basal forebrain area and inhibits arousal neurons there. – Adenosine also stimulates sleep in the preoptic area. • This area also responds to warming and probably accounts for fever-induced sleepiness. – Neurons in the ventrolateral preoptic area double their firing during sleep. • They inhibit neurons in arousal areas. • Different parts induce REM and non-REM sleep. The pons sends impulses to the magnocellular nucleus of the medulla to produce the atonia of REM sleep. Brain Mechanisms of Sleep Figure 15.9 Sleep and Dreaming • The arousal system consists of two major pathways. – The PPT/LDT • enables transmission through the thalamus to the cortex • and shifts the EEG to high-frequency, low amplitude activity. (This pathway also is active in the shift to REM sleep.) ◊ Sleep and Dreaming – The second pathway activates the cortex to receive inputs from the thalamus. • The locus coeruleus and raphé nuclei are active during waking, relatively quiet during non-REM, and almost silent during REM. • The tuberomamillary nucleus and the basal forebrain area arouse the cortex. • Neurons in the lateral hypothalamus send orexin-releasing axons to several arousal centers. • Orexin may stabilize the system by preventing inappropriate switching into sleep. Activity in the (a) locus coeruleus and (b) raphé nuclei from waking to post-REM. Arousal Structures of Sleep and Waking Figure 15.10 Sleep and Dreaming – REM sleep is characterized by PGO waves • They travel from the pons through the lateral geniculate nucleus of the thalamus to the occipital area. • They apparently initiate the EEG desynchrony of REM sleep. • They may account for the visual imagery of dreaming. Sleep and Dreaming • Insomnia is the inability to sleep or to obtain adequate quality sleep, to the extent that the person feels inadequately rested. – Insomnia has also been linked to health conditions such as obesity and decreased longevity. – Insomnia is • linked to stress; • more common in people with affective disorders; • often made worse by the use of sleeping pills; • related to your chronotype, which indicates how your internal clock is synchronized to the 24-hr day. Chronotype and Sleep Disruption Figure 15.14 (a) Ordinarily, a person falls asleep when body temperature (shown in red) is decreasing and awakens as it is rising. (b) If body temperature is phase delayed, the person has trouble falling asleep. (c) If body temperature is phase advanced, the person wakes up early. Sleep and Dreaming Bedwetting, night terrors, and sleep walking occur during slow wave sleep. Although sleepwalking is most frequent in childhood, about 3% to 8% of adults sleepwalk. Sleepwalking is at least partially genetic, and can be triggered by stress, alcohol, and sleep deprivation. Sleepwalking has even been used as a defense in crimes committed, allegedly, during a sleepwalking episode. Sleep-related eating disorder is a condition in which people raid the refrigerator while they are asleep, often consuming junk food and gaining considerable weight. ◊ Sleep and Dreaming Narcolepsy is a disorder in which individuals fall asleep suddenly during the daytime and go directly into REM sleep. People with narcolepsy do not have clear boundaries between sleep and waking, possibly due to abnormalities in the orexin system. Narcoleptic dogs have a mutated orexin receptor gene . • In humans, orexin-secreting neurons apparently are destroyed by an autoimmune reaction, due to an HLA immune system gene. Another symptom of narcolepsy is cataplexy, in which the person falls to the floor paralyzed but fully awake. Cataplexy in a Dog Figure 15.15 Sleep and Dreaming REM sleep behavior disorder is almost the opposite of cataplexy. People with this disorder lack the usual REM atonia and are uncharacteristically physically active during REM sleep, often to the point of injuring themselves or their bed partners. It is often associated with a neurological disorder, such as Parkinson’s disease or a brain stem tumor. Lewy bodies in the medulla may affect the ability of the magnocellular nucleus to produce the atonia of REM sleep. ◊ Sleep and Dreaming • How conscious are we during sleep? – According to Francis Crick, REM sleep is a state of diminished consciousness and we are unconscious during non-REM sleep. – Lucid dreamers are semi-conscious; they are aware they are dreaming and can manipulate their dreams. – Sleepwalkers engage in many activities during non-REM sleep that we would expect to see only in the waking state, such as driving a car and eating. • One solution is to think of sleep as a different state of consciousness along a continuum of consciousness. The Neural Basis of Consciousness • Consciousness – refers to a state: a person is conscious or unconscious; – indicates a sense of conscious experience, or awareness of something. • Consciousness varies in level, with coma and deep anesthesia on one extreme, alert wakefulness on the other, and sleep in between. • There are also altered states of consciousness, including hypnosis, trances, and meditative states. • Most researchers agree that consciousness involves awareness, attention, and a sense of self. The Neural Basis of Consciousness • Several brain areas are considered important in awareness. – The prefrontal cortex—it is active when a subject becomes aware of a relationship between stimuli. – The hippocampus, due to its role in declarative learning. – The parietal lobes—its ability to locate objects in space is considered necessary for combining an object’s features into a conscious whole. • Example: A patient with parietal lobe damage often attributed an object’s color or movement to another object. The Neural Basis of Consciousness – Researchers have concluded that binding an object’s characteristics involves synchronization of neural activity. • For example, while viewing a moving object activity becomes synchronized between V1 and V5 (which processes movement). • Synchronization involves brain activity in the gamma range (30 - 90 Hz). – However, much of behavior occurs outside awareness. • Use of proprioceptive cues to maintain posture. • Blindsight detection of “unseen” objects. • Learning without awareness. The Neural Basis of Consciousness • Attention involves focusing on some neural inputs to the exclusion of others. – The Cheshire cat effect demonstrates how powerful attention is. – The four-fold increase in car accidents while drivers are using a mobile phone demonstrates that attention allocates limited resources. • There are two attention networks. – The dorsal network allocates attention under goal-directed control. – The ventral network responds to stimulus demands. The Neural Basis of Consciousness – The anterior cingulate cortex (ACC) may play an executive role in allocating attention. • About 1 out of every 5 ACC neurons increases or decreases firing during attention-demanding tasks. • The ACC is active when the subject must rapidly read color names printed in a non-congruent color (“green” printed in blue). • The researchers believe the ACC modulates activity in attentional pathways to focus attention on the word’s meaning and suppress attention to its color. ◊ The Neural Basis of Consciousness An important aspect of consciousness is a sense of self. – The sense of self includes • identity – what we refer to as “I” • and a sense of agency, the attribution of an action or effect to ourselves. Mirror recognition studies suggest that sense of self develops around 15 months of age. – A few other species share this sense of self. • Chimps, orangutans, elephants, porpoises, and even magpies can recognize themselves in a mirror. • Monkeys do not even, after 17 years of exposure. The Neural Basis of Consciousness • What are the neural correlates of sense of self? – Damage to frontal-temporal areas that impairs episodic memory can produce a detachment from the self. – People with damage to the ACC and the insula may treat their mirror image as a companion, intruder, or stalker. – The insula and inferior parietal cortex appear to distinguish between self as agent and other as agent. • When subjects perceived they were controlling movements on a computer, activity increased in the insula; activity shifted to the inferior parietal cortex when the experimenter controlled. • Schizophrenics who believe their behavior is controlled by others show heightened parietal lobe activity. The Neural Basis of Consciousness Body image is an important aspect of the sense of self; we identify our body with our self. – Body image: • is so strong that it persists in the face of amputation, resulting in phantom limb in 80% of amputees. • is so strong that an amputee whose phantom arm extended to the side had to walk sideways through doors. • appears to be inborn, because even children born with missing limbs experience phantoms. Body image resides primarily in parietal areas; damage or malfunction leads to illusions such as denial that a limb is paralyzed and out-of-body experience. The Neural Basis of Consciousness • Long-term memory is essential to the sense of self. – People who have lost their past memories have an impaired sense of self. – Korsakoff’s patients often confabulate, replacing missing memories. As Sacks said, one patient had to “make himself (and his world) up every moment.” – Memory of the past “is what makes us us”—McGaugh – Short-term memory loss has less effect. • HM, for example, had many years of memories as a background for interpreting current experience. ◊ The Neural Basis of Consciousness • Researchers believe that mirror neurons contribute to development of one’s theory of mind, which involves a distinction between self and others. – Inability of the anterior cingulate cortex to regulate mirror neuron activity may explain autistic individuals’ deficiencies in theory of mind. – Mirror neurons are important in assessing others’ intention. • Mirror neurons distinguished between the apparent intent of a model reaching for food to eat versus reaching to clean up. The Neural Basis of Consciousness • Severing the corpus callosum to control seizures creates a unique disorder of self. – The hemispheres often engage in independent or even conflicting behavior. • One man shook his wife with his left hand (controlled by the more emotional right hemisphere) while his right hand tried to restrain the left. • When the right hand is performing a spatial task, the left hand (controlled by the more spatially capable right hemisphere) sometimes intercedes. ◊ The Neural Basis of Consciousness • The left hemisphere can give an accurate explanation why the right hand chose a picture of a chicken; but it says the left hand chose the shovel “to clean out the chicken shed” (rather than to shovel snow). According to Gazzaniga, the left hemisphere is the “brain interpreter” that integrates all ongoing cognitive processes; the right hemisphere has a more primitive form of consciousness. But researchers who consider the right hemisphere as “less conscious” may be confusing consciousness with the ability to verbalize the content of consciousness. The Neural Basis of Consciousness Dissociative identity disorder involves shifts in consciousness and behavior that appear to be distinct personalities. Childhood physical and/or sexual abuse is reported in 90-95% of cases. The development of alternate personalities might be a way the child escapes from persistent abuse. Alters can differ in handedness, response to medications, immune reactions, and physiological measures such as heart rate. The hippocampus increases and decreases activity when switching, consistent with Bowen’s view that state-dependent learning is involved. The Neural Basis of Consciousness • Most theories of consciousness assume that consciousness involves a widely distributed network. – As subjects become conscious of a visuallypresented stimulus, activity spreads from visual to prefrontal areas and then through most of the brain. – One hypothesis is that gamma oscillations generated by a feedback loop between the thalamus and cortex binds sensory information into awareness. – In addition, activity in the default mode network varies with levels of consciousness. Awareness and Arousal in Consciousness Figure 15.27 • The various states of consciousness can be described along two continua, awareness and arousal. The Neural Basis of Consciousness Brain damage produces various deficiencies in consciousness; these must be understood and assessed to determine prognosis and potential for communication. Coma: unarousable and unresponsive to stimulation Vegetative state: reflexive responses to stimulation and sleep cycling, but no voluntary interaction Minimal consciousness: some voluntary responses but inability to communicate reliably Locked-in syndrome: full consciousness, but mostly uncommunicative because of paralysis (due to brain stem lesions) Vegetative patients have communicated with researchers by producing distinctive patterns of brain activity. PET Scans of Various Levels of Consciousness