Lecture – 14 Dr. Zahoor Ali Shaikh SLEEP AND EEG
SLEEP What is Sleep ? • Sleep is a state when person is not aware of surrounding. Sleep is active process. It consist of two processes. 1. Non-Rapid Eye Movement (NREM) or slow wave sleep 2. Rapid Eye Movement (REM) or paradoxical sleep
What is Consciousness? • It is awareness of external world or surrounding. Level of Consciousness (states in decreasing order) • Maximum alertness • Wakefulness • Sleep • Coma
Level of Consciousness Maximum alertness • It depends on high activity level of central nervous system, reticular activating system (RAS). Wakefulness • Awake person is aware of surrounding.
Level of Consciousness Sleep • Sleep is an active process, brain overall activity is not reduced. • Sleeping people are not consciously aware of surrounding, but they have inward conscious experience e.g. dreams. • They can be aroused by external stimuli e.g. alarm. Coma • It is total unresponsiveness of a living person to external stimuli due to brain damage that interferes with RAS or severe depression of cerebral cortex.
RETICULAR FORMATION What is Reticular Formation? • It is network of interconnected neurons, which run through the entire brain-stem and into the thalamus. • Reticular formation receives all incoming sensory input.
RETICULAR FORMATION [cont] • Ascending fibers originating from reticular formation carry signals upwards to arouse and activate the cerebral cortex. These fibers are called Reticular Activating System.
RETICULAR FORMATION • RAS controls the cortical alertness. • Fibers descending from cortex especially motor cortex can activate RAS. • Centers that govern sleep are within the brain-stem, but recent evidence suggest that the center for slow sleep (NREM) lie in the hypothalamus.
SLEEP • Two types of Sleep i). NREM Sleep or slow wave sleep ii). REM sleep or paradoxical sleep • We spend 80% time in NREM sleep and 20% time in REM sleep. • They are characterized by different EEG patterns and different behavior. We will discuss each one.
i).NREM Sleep or slow wave sleep • Slow wave sleep has four stages. During these stages ( I- IV) there is progressive slowing of EEG waves and EEG waves become high amplitude, hence it is called Slow wave sleep. • NREM Stages are called: Stage I Stage II Stage III Stage IV
NREM Sleep or slow wave sleep Stage I • At one set of sleep, Stage I is referred as drowsiness or pre-stage of sleep. Stage II • Light sleep. Stage III and IV • Deep sleep
NREM Sleep or slow wave sleep • At one set of sleep, we move from light sleep of Stage I to deep sleep of Stage IV during a period of 60-70mins . • After Stage I to IV of NREM sleep, we get 10-20 mins episode of REM or paradoxical sleep. • Then we reverse to NREM – REM cycle again.
NREM Sleep or slow wave sleep • A person has 5-6 cycles of sleep i.e. NREM-REM, again NREM-REM throughout the night. • Time for each stage of sleep during one cycle: Stage I – 3-5% [5-10mins] Stage II – 50-60% [30-40mins] Stage III & IV – 10-20% [10-20mins] REM sleep – 10-20% [10-20mins] • Note – Time for REM sleep increases during each cycle.
REM SLEEP • During REM sleep, rapid eye movement occur. • Muscle tone throughout body is decreased • EEG pattern during REM cycle abruptly gets similar to that of wake, alert person, although person is in sleep, therefore, it is called paradoxical sleep (person sleeping but EEG pattern is like awake person).
SLEEP • Infants spend more time in REM sleep. New born sleeps about 16-20 hrs/day. • In children, NREM and REM become 50% each. During childhood, child sleeps 10-15 hrs/day.
SLEEP • Adult person needs 6-9 hours of sleep. He spends 80% time in NREM sleep and 20% in REM sleep • In elderly NREM Stage IV (deep sleep) and REM sleep decreases. Old person sleeps 5-6 hrs
Electroencephalogram What is EEG? • EEG is the record of electrical activity of brain (superficial layer i.e. the dendrites of pyramidal cells) by placing the electrodes on the scalp. • We record EEG with electrodes over the scalp. • We record different types of waves during different stages of sleep.
Electroencephalogram • German physiologist and psychiatrist Hans Berger recorded the first human EEG in 1924. • It is one of the most remarkable development in the history of clinical neurology Hans Berger
EEG Waves recorded are • Alpha wave -- 8 – 13 Hz. • Beta wave -- >13 Hz. (14 – 30 Hz.) • Theta wave -- 4 – 7.5 Hz. • Delta waves – 1 – 3.5 Hz. • D T A B
Alpha wave • rhythmic, 8-13 Hz • mostly on occipital lobe • 20-200 μ V • normal, • relaxed awake rhythm with eyes closed
Beta wave • irregular, 14-30 Hz • mostly on temporal and frontal lobe • Recorded during mental activity, awake person (eyes open). • excitement
Theta wave • rhythmic, 4-7 Hz • Stage II and Stage III sleep
Delta wave • slow, < 3.5 Hz • Stage III, IV sleep
EEG WAVES DURING DIFFERENT STAGES OF SLEEP • NREM SLEEP Stage I– high frequency EEG activity alpha, replaced by slower waves Stage II – slow waves theta (θ) Stage III - Theta (θ) - Delta(δ) waves Stage IV – Delta(δ) waves • REM • Rapid low voltage, EEG activity like stage I of NREM. • Eye movements are recorded. • Person is in deep sleep, difficult to wake.
BEHAVIORAL PATTERN DURING SLEEP • Night mares occur in stage III and IV. • People especially children walk and talk during stage III and IV. • Dream occur during REM sleep. Brain imaging during REM sleep shows increase activity in visual area and limbic system and decreased activity in Prefrontal area reflecting dreams are related to emotional memory bank but not to thinking.
SLEEP WAKE CYCLE • Sleep wake cycle is controlled by three neural system. 1. Arousal system – regulated by group of neuron in hypothalamus and involves reticular activating system (RAS) originating in brain-stem. 2. Slow wave sleep center (NREM) – In the hypothalamus, it has neurons that induce sleep. 3. REM sleep center in the brain-stem – it has neurons which become active during REM sleep
FUNCTIONS OF SLEEP What is Function of Sleep? • It is not clear. We spend 1/3 of our life sleeping. • During Sleep brain cells are not resting, but there is change in the activity.
What is the purpose of NREM and REM sleep? Theories are 1. During metabolic activity of neuron and glial cells, Adenosine is produced from the ATP during awake state (increased adenosine when we are awake more). • Adenosine inhibits arousal center, this can bring NREM sleep (injection of adenosine induces normal sleep).
What is the purpose of NREM and REM sleep? [cont] • During sleep , Adenosine level decreases as brain uses this adenosine for replenishing its limited energy stores. • Caffeine blocks adenosine receptors in the brain, therefore causes wakefulness.
What is the purpose of NREM and REM sleep? [cont] 2.Restoration and recovery proposal During awake, brain neuron release neurotransmitter Norepinephrine and Serotonin. • But during REM sleep, these neurotransmitters are not released, therefore, it restores receptor sensitivity.
What is the purpose of NREM and REM sleep? [cont] 3.Sleep is necessary for learning and memory This may explain Why infants need so much sleep.
SLEEP DISORDERS • Insomnia - Insomnia is difficulty in getting sleep - 10-15% of population suffer from insomnia - cause of Insomnia- may be anxiety, too much coffee, tea, soft drink, stimulants, drugs , travelling . • Narcolepsy • Rare disorder affects 0.5% population. • Person suddenly falls asleep at odd moments. • May occur frequently throughout the day. • Sleep Apnea syndrome - person not breathing for a while, snoring , obesity, little sleep.
EEG showing sleep spindle STAGE II K - complex Sleep Spindle
USE OF EEG • EEG is useful in diagnosis of 1. Epilepsy 2. Sleep Disorders 3. Brain death [used in some centers]
POLYSOMNOGRAPHY • Polysomnography is a series of tests performed on a patient with sleep disorders e.g. sleep apnea, narcolepsy • It is over night procedure and includes monitoring of ECG, blood pressure, air flow, blood oxygen level, EEG, eye movements, and movements of respiratory muscle and limbs
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