Lecture 20- Sleep and Arousal.pdf

Sleep & Arousal Dr. Kelly Roballo Learning Objectives 1. Describe the behavioral, EEG, and other characteristics of the stages of slow-wave sleep and rapid-eyemovement (REM) sleep. 2. Describe the neurochemical systems important for the regulation of sleep and waking. 3. Describe narcolepsy and sl...

Sleep & Arousal Dr. Kelly Roballo Learning Objectives 1. Describe the behavioral, EEG, and other characteristics of the stages of slow-wave sleep and rapid-eyemovement (REM) sleep. 2. Describe the neurochemical systems important for the regulation of sleep and waking. 3. Describe narcolepsy and sleep apnea. 4. Describe the changes in the sleep cycle across the life cycle. 5. Describe insomnia and restless leg syndrome. Sleep • Sleep is defined by the normal suspension of consciousness and specific brain wave criteria • Getting too little sleep creates a “sleep debt” that must be repaid in the following days Purves, Neuroscience 4th ed. • One function of sleep is to replenish brain glycogen levels, which fall during the waking hours Purves, Neuroscience 4th ed. • In humans, lack of sleep leads to impaired memory and reduced cognitive abilities and, if the deprivation persists, mood swings and often hallucinations • Genetic disease “fatal familial insomnia” appears in middle age, is characterized by hallucinations, seizures, loss of motor control, and the inability to enter a state of deep sleep—patients die within several years of onset *Clinical Correlation The Circadian Cycle of Sleep and Wakefulness Humans have an internal ‘clock’ that operates even in the absence of external information about the time of day The principal circadian clock, the suprachiasmatic nucleus (SCN), is located in the hypothalamus Hastings, M.H., Maywood, E.S. & Brancaccio, M. Generation of circadian rhythms in the suprachiasmatic Purves, Neuroscience 4th ed. nucleus. Nat Rev Neurosci 19, 453–469 (2018). https://doi.org/10.1038/s41583-018-0026-z • The receptors that sense the light changes are located within the ganglion cell layer of retina • these photoreceptors contain melanopsin, and are depolarized by light (rods and cones) • the axons runs the retinohypothalamic tract, which projects to the suprachiasmatic nucleus (SCN) of the anterior hypothalamus Purves, Neuroscience 4th ed. Brain Waves: Alpha and Beta Alpha waves • occur at 8 -13 Hz • mostly from occipital cortex but can also be found in frontal and parietal regions as well • occur during quiet resting states of cerebration, they disappear when there is a specific mental activity (opening of the eyes, intense mental concentration or stress) or during sleep • will not occur without cortical connection to thalamus Beta waves • occur at 14 - 80 Hz • occur during intense mental activity or stress Brain Waves: Theta and Delta Theta waves Delta waves • occur at 4 - 7 Hz • recorded from parietal and temporal regions in children • occur during emotional stress in adults particularly in response to disappointment or frustration • all waves below 3.5 Hz • occur during deep sleep; thought to be activity of the cortex independent of signals from lower brain areas Brain Waves Guyton & Hall, Medical Physiology, 11th ed. BRAIN WAVE EYE MOVEMENT MUSCLE TONE Prominent posterior alpha (8-12 Hz) rapid high Rapid CNS responses, regular breathing Alpha disappears; theta slowing (4-7 Hz) slow, rolling moderate Slow CNS responses, periodic breathing, sleep apnea 2 K-complexes, 12-14 Hz Sleep spindles none low Subjective sleep onset, decreased seizure threshold, sleep apnea 3 20% of EEG is delta activity low High arousal threshold, night terrors and sleep walking, regular breathing 4 50% of EEG is delta activity very low Rhythm but, hypo-ventilation; dreams, muscle paralysis, low ventilatory drive, sleep apnea BRAIN STATE Wake 1 REM none rapid Low voltage, mixed frequency PHYSIOLOGY & PATHOLOGY Stages of Sleep drowsiness light sleep slow wave sleep non-REM Purves, Neuroscience 4th ed. • The typical 8 hours of sleep comprise several cycles alternating between nonREM and REM sleep • The amount of REM sleep decreases by age • REM sleep is characterized by dreaming • Since most muscles are inactive during REM sleep, the motor responses to dreams are relatively minor • The relative physical paralysis during REM sleep arises from increased activity in GABAergic neurons in the pontine reticular formation Non-REM sleep • Slow, rolling eye movements • Decreases in muscle tone, heart rate, breathing, blood pressure • Decrease in metabolic rate, body temperature Purves, Neuroscience 4th ed. • Abnormalities in delta sleep, or deep sleep, are common in individuals with depression. • Delta sleep begins in sleep stage 3, and by sleep stage 4 delta waves make up more than 50% of the EEG recording. • This disturbance in delta sleep may not allow a depressed individual ample opportunity to physically restore the body • In depression, multiple awakenings are common. • Patients with depression shows a shortened period of REM latency. • REM latency is the elapsed time between onset of sleep and the first REM sleep. *Clinical Correlation • The circuitry involved in the decreased sensation and muscle paralysis of the REM sleep Purves, Neuroscience 4th ed. REM stage • The increase in limbic system activity, coupled with a marked decrease in the influence of the frontal cortex during REM sleep explains some characteristics of dreams Purves, Neuroscience 4th ed. Important nuclei in regulation of the sleep-wake cycle Purves, Neuroscience 4th ed. Hypothalamic nuclei involved in sleep • Activation of VLPO neurons contributes to the onset of sleep • lesions tends to produce insomnia Purves, Neuroscience 4th ed. Blumenfeld, Neuroanatomy NonREM n During nonREM sleep, GABAergic neurons inhibit histaminergic neurons. This removes histaminergic activation from the forebrain and from brainstem cholinergic neurons. Certain regions of the medulla may also play a role in nonREM sleep Blumenfeld, Neuroanatomy REM n During REM sleep, REM-on cells and REM-waking-on cells in the pontine reticular formation interact with other brainstem circuits to activate cholinergic inputs to the thalamus, inhibit tonic muscle activity, activate phasic eye movements Thalamocortical Interactions In the tonic firing state, thalamic neurons transmit information to the cortex that is encoding peripheral stimuli In the oscillatory mode, they become synchronized with those in the cortex, “disconnecting” the cortex from outside world Purves, Neuroscience 4th ed. Thalamocortical Feedback Loop Purves, Neuroscience 4th ed. In Summary… • The control of sleep and wakefulness depends on brainstem and hypothalamic modulation of the thalamus and cortex • It is the thalamocortical loop that generates the EEG signature of mental function along the continuum of deep sleep to high alert Purves, Neuroscience 4th ed. Sleep disorders • Insomnia, is the inability to sleep for a sufficient length of time • Stress, jet lag, too much caffeine • Depression: impaired balance between modulatory systems that control the sleep cycles • Sleep apnea, is a pattern of interrupted breathing during sleep • The airway collapses during breathing, and blocks the airway *Clinical Correlation Sleep apnea • Patients awake frequently and never descend into stages III or IV sleep Purves, Neuroscience 4th ed. Sleep disorders • Restless Leg syndrome, represents with unpleasant prickling, or tingling sensations in one or both legs and feet, and an urge to move them about to obtain relief • In severe cases, benzodiazepins may help • Narcolepsy, represents with frequent “REM sleep attacks” (lasting 30 sec to 30 min) during the day • They enter REM sleep from wakefulness without going through non-REM sleep *Clinical Correlation Thank you Neural Circuits Governing Sleep • The saccade-like eye movements of REM sleep arise because endogenously generated signals from the pontine reticular formation are transmitted to the motor region of the superior colliculus • Specific EEG waves of REM sleep originate in the pontine reticular formation and propagate through the lateral geniculate nucleus of the thalamus to the occipital cortex • Pontine-geniculo-occipital (PGO) waves