Electroencephalogram and Sleep

Introduction

The electroencephalogram provides a noninvasive record of the brain’s electrical activity and is an essential tool for studying sleep. Analysis of brain wave patterns helps identify different sleep stages, evaluate sleep disorders, and understand the physiological importance of restorative slow-wave sleep and rapid eye movement sleep.

Electroencephalogram

• The electroencephalogram is a recording of the brain’s spontaneous electrical activity obtained from electrodes placed on the scalp.
• It primarily reflects the summed postsynaptic potentials generated by large populations of cortical neurons.
• The recorded electrical signals arise mainly from synchronized excitatory and inhibitory synaptic activity rather than individual action potentials.
• Cortical electrical activity is strongly influenced by inputs from the thalamus and the brainstem reticular activating system.
• These inputs synchronize cortical neurons and generate characteristic rhythmic brain wave patterns.
• Electroencephalography is the technique used to record the electroencephalogram.
• The recording is obtained using an instrument called an electroencephalograph.
• Electroencephalography is an important diagnostic tool for evaluating epilepsy, altered consciousness, and sleep disorders.
• It is also widely used to study normal brain function and different stages of sleep.

Procedure of Recording

• Electroencephalography records the brain’s electrical activity using surface electrodes placed on the scalp.
• Because electroencephalogram signals are of very low amplitude, they require amplification before recording.
• Recordings may use bipolar leads, which compare potentials between two active electrodes.
• They may also use unipolar (referential) leads, which compare one active electrode with a reference electrode.
• Silver or silver–silver chloride disc electrodes are commonly used because they provide stable electrical recordings.
• The subject is positioned comfortably with adequate head support to minimize movement artifacts.
• Electrodes are placed at standardized scalp locations according to the International 10–20 System.
• Multiple channels record electrical activity simultaneously from different cortical regions.
• Modern digital electroencephalography systems store, process, and analyze recordings using computer software.
• Standardized recording techniques improve reproducibility and facilitate accurate clinical interpretation of electroencephalogram findings.

EEG Waves

• Electroencephalogram waves are characterized by their frequency and amplitude.
• In healthy adults, frequencies usually range from 1 to 30 hertz, while amplitudes typically range from 20 to 100 microvolts.
• The electroencephalogram changes according to the level of consciousness and cortical activity.
• During wakefulness and alertness, brain waves are predominantly high in frequency and low in amplitude because cortical neurons discharge asynchronously.
• During deep sleep, waves become lower in frequency and higher in amplitude due to synchronized neuronal activity.
• Persistent absence of cerebral electrical activity, when interpreted with appropriate clinical criteria, supports the diagnosis of brain death.
• Electroencephalogram rhythms are classified into alpha, beta, theta, and delta waves.

Alpha Rhythm

• Alpha rhythm is the dominant pattern in a relaxed, awake adult with the eyes closed.
• Alpha waves have a frequency of 8–13 hertz and an amplitude of approximately 50–100 microvolts.
• They are most prominent over the parietal and occipital regions of the scalp.
• Opening the eyes or engaging in mental activity suppresses alpha waves.
• This phenomenon is called alpha block or desynchronization and reflects increased cortical activation.

Alpha Block

• Alpha block is a normal physiological response indicating alertness.
• The frequency of alpha waves is influenced by metabolic and physiological factors.

Factors affecting α Wave Frequency

• Hypoglycemia, hypothermia, elevated arterial pressure, and reduced glucocorticoid levels tend to decrease alpha frequency.
• In contrast, increased body temperature, higher blood glucose levels, reduced arterial pressure, and elevated glucocorticoid levels generally increase alpha wave frequency.
• Interpretation of electroencephalogram patterns must always be correlated with the individual’s clinical state.

Beta Rhythm

• Beta waves have a frequency of 13–30 hertz and a low amplitude of approximately 5–10 microvolts.
• Beta activity is most prominent during wakefulness when the eyes are open and the individual is mentally alert.
• These waves are commonly recorded over the frontal and parietal regions of the cerebral cortex.
• Increased beta activity is associated with active thinking, concentration, and sensory processing.

Theta Rhythm

• Theta waves have a frequency of 4–8 hertz and a relatively high amplitude.
• They are a normal finding in infants and young children.
• Theta activity also appears during light to moderate non-rapid eye movement sleep in healthy adults.
• Persistent theta waves during wakefulness in adults may indicate drowsiness or underlying neurological dysfunction, although they may also occur transiently under certain physiological conditions.

Delta Rhythm

• Delta waves have the lowest frequency, ranging from 0.5–4 hertz, and the highest amplitude, usually 20–200 microvolts.
• Delta activity predominates during deep non-rapid eye movement sleep.
• The presence of persistent delta waves in an awake adult usually suggests significant cerebral dysfunction or structural brain disease.

EEG Rhythms in Infants and Children

• Electroencephalogram patterns change progressively with normal brain maturation.
• Newborns and infants show predominantly irregular low-frequency activity with intermittent faster rhythms.
• During childhood, theta activity becomes more prominent.
• With increasing age, alpha rhythm gradually develops and becomes the dominant resting rhythm by adolescence.
• In healthy adults, alpha activity is most prominent over the occipital region when the eyes are closed.

Neural Basis of EEG

• The electroencephalogram mainly reflects the summed postsynaptic potentials generated by cortical pyramidal neurons.
• These neurons are arranged in parallel, with their apical dendrites oriented perpendicular to the cortical surface.
• Excitatory and inhibitory synaptic activity generates extracellular current flow around these neurons.
• This electrical activity produces a dipole between regions of current entry and current exit.
• Simultaneous activation of large numbers of similarly oriented pyramidal neurons generates electrical fields that are detected by scalp electrodes.
• Synchronization of neuronal activity increases electroencephalogram amplitude, whereas asynchronous activity produces low-amplitude, high-frequency waveforms.

Sleep and EEG

• Sleep is a reversible physiological state of reduced awareness from which an individual can be awakened by appropriate sensory stimuli.
• It is essential for normal physical growth, brain function, tissue repair, memory consolidation, and overall health.
• Wakefulness is maintained by the reticular activating system, whereas sleep begins when the activity of this system decreases.
• Sleep is produced through coordinated interactions between the brainstem, hypothalamus, and cerebral cortex.
• Normal sleep occurs in recurring cycles throughout the night.
• Each sleep stage has characteristic electroencephalogram, autonomic, and endocrine changes.
• Sleep is broadly classified into non-rapid eye movement sleep and rapid eye movement sleep.
• Non-rapid eye movement sleep is also called slow-wave sleep because of its characteristic electroencephalogram pattern.
• Rapid eye movement sleep is called paradoxical sleep because brain activity resembles wakefulness despite reduced skeletal muscle tone.
• Alternation between these two phases is essential for restorative sleep and normal neurological function.

Sleep Cycles

• Normal sleep is organized into repeated sleep cycles that occur throughout the night.
• Each cycle lasts approximately 70–90 minutes, with an average duration of about 90 minutes.
• A typical adult experiences 4–6 sleep cycles during 7–8 hours of sleep.
• Sleep usually begins with non-rapid eye movement sleep.
• Non-rapid eye movement sleep progresses through increasingly deeper stages before transitioning to rapid eye movement sleep.
• After deep sleep, the brain enters the rapid eye movement sleep phase.
• Completion of rapid eye movement sleep marks the end of one sleep cycle.
• The next cycle begins again with the lightest stage of non-rapid eye movement sleep.
• Deep non-rapid eye movement sleep predominates during the first half of the night.
• In contrast, rapid eye movement sleep becomes progressively longer during the later part of sleep.
• The first rapid eye movement episode usually occurs about 70–90 minutes after sleep onset.
• In healthy adults, rapid eye movement sleep accounts for approximately 20–25% of total sleep time.
• The proportion of individual sleep stages varies with age, health status, and individual physiological characteristics.
• This cyclic organization is essential for normal physical restoration, memory consolidation, and optimal brain function.

Slow Wave Sleep (Non-REM Sleep)

• Non-rapid eye movement sleep consists of progressively deeper stages that promote physical restoration and recovery.
• As sleep deepens, the electroencephalogram shows progressively lower frequencies and higher amplitudes due to increased neuronal synchronization.
• Arousal becomes progressively more difficult in the deeper stages of non-rapid eye movement sleep.

Stage 1

• Stage 1 is the transition between wakefulness and sleep.
• It is characterized by drowsiness and replacement of relaxed wakeful activity with low-amplitude mixed-frequency brain waves.
• Muscle activity and awareness of the surroundings begin to decrease.

Stage 2

• Stage 2 represents stable light sleep and occupies the largest proportion of total sleep time in healthy adults.
• The characteristic electroencephalogram features of this stage are sleep spindles and K-complexes.

Sleep Spindles

• Sleep spindles are brief bursts of 12–14 hertz rhythmic activity that last approximately 0.5–2 seconds.
• They are believed to support memory consolidation and reduce responses to external sensory stimuli.
• K-complexes are high-amplitude waveforms that help maintain sleep despite external disturbances.

K-Complexes

K-complexes are high-amplitude electroencephalogram waves occurring intermittently during Stage 2 sleep.

Stage 3

• Stage 3 is characterized by moderately deep non-rapid eye movement sleep with slower, higher-amplitude electroencephalogram waves.

Stage 4

Stage 4 represents the deepest stage of non-rapid eye movement sleep and is dominated by delta waves.

Autonomic and other Changes during Slow Wave Sleep

• Delta activity is widespread across the cerebral cortex during this stage.
• Arousal is most difficult during deep slow-wave sleep because the threshold for awakening is highest.
• Deep sleep is especially important for physical restoration and recovery.
• During slow-wave sleep, heart rate, blood pressure, and body temperature decrease.
• Respiration becomes slow, regular, and energy efficient.
• Gastrointestinal activity increases because of enhanced parasympathetic activity.
• Skeletal muscle tone is reduced, but complete muscle paralysis does not occur.
• Rapid eye movements are absent throughout non-rapid eye movement sleep.

Control Mechanisms of Slow Wave Sleep

• Slow-wave sleep is regulated by coordinated neural circuits and chemical messengers that reduce cortical arousal.
• These mechanisms promote restorative sleep and maintain the normal sleep–wake cycle.

Neural Control Mechanisms

Neural regulation can be divided into afferent, central, and circadian mechanisms.

Afferent Control

• Repetitive, monotonous sensory stimulation with low-frequency input reduces cortical activation and facilitates sleep onset.
• This effect is mediated through brainstem pathways that activate sleep-promoting centers.
• Several brain regions participate in the generation of slow-wave sleep.

Central Control

• The preoptic area of the anterior hypothalamus is a major sleep-promoting center.
• Neurons in this region inhibit wake-promoting pathways and facilitate non-rapid eye movement sleep.
• The medullary reticular formation also contributes to the initiation and maintenance of slow-wave sleep.
• Thalamic networks synchronize cortical activity, producing the characteristic slow, high-amplitude electroencephalogram waves.

Circadian Control

• The suprachiasmatic nucleus of the hypothalamus functions as the biological clock.
• It receives light information from the retina through the retinohypothalamic pathway.
• This input synchronizes the sleep–wake cycle with the environmental light–dark cycle.
• Damage to the suprachiasmatic nucleus disrupts circadian rhythms and alters normal sleep patterns.

Chemical Control Mechanisms

• Neurotransmitters and neuromodulators play essential roles in sleep regulation.
• Serotonin released from the raphe nuclei contributes to the regulation of non-rapid eye movement sleep.
• Noradrenaline released from the locus coeruleus promotes wakefulness and cortical activation.
• Reduced noradrenergic activity favors the onset of sleep.
• Increased catecholamine activity enhances alertness and suppresses sleep.
• Acetylcholine released from pontine neurons contributes mainly to cortical activation and plays a greater role during rapid eye movement sleep than during slow-wave sleep.
• Adenosine accumulates in the brain during prolonged wakefulness.
• Rising adenosine levels increase sleep pressure and facilitate sleep onset.
• Caffeine promotes wakefulness by blocking adenosine receptors.
• Prostaglandin D₂ promotes sleep by acting on sleep-regulating regions of the hypothalamus.
• In contrast, prostaglandin E₂ favors wakefulness and reduces slow-wave sleep.
• Balanced interactions among neurotransmitters determine transitions between wakefulness and different sleep stages.
• Normal slow-wave sleep supports tissue repair, immune function, energy conservation, and memory consolidation.
• Disturbances in these neural or chemical mechanisms can produce insomnia, fragmented sleep, or circadian rhythm disorders.
• Proper synchronization of sleep-regulating pathways is essential for maintaining healthy cognitive and physiological function.

Table 136.1: Differences between NREM and REM sleep.

Feature	Non-Rapid Eye Movement Sleep	Rapid Eye Movement Sleep
Position in sleep cycle	Begins each normal sleep cycle	Follows non-rapid eye movement sleep
Proportion of sleep	About 75–80% of total sleep	About 20–25% of total sleep
Autonomic activity	Reduced heart rate, blood pressure, and respiration	Variable heart rate, blood pressure, and respiration with increased sympathetic activity
Eye movements	Absent	Rapid eye movements present
Dreaming	Less vivid and less frequently recalled	Vivid dreams with better recall
Muscle tone	Reduced	Markedly suppressed except for eye and respiratory muscles
Electroencephalogram	High-amplitude, slow waves in deep sleep	Low-amplitude, high-frequency activity resembling wakefulness
Primary control	Sleep-promoting hypothalamic pathways	Pontine sleep-generating circuits

Paradoxical Sleep (REM Sleep)

• Rapid eye movement sleep begins after a period of non-rapid eye movement sleep and recurs cyclically throughout the night.
• It usually lasts 10–20 minutes in early sleep cycles and becomes progressively longer toward morning.
• The electroencephalogram changes abruptly from slow, synchronized waves to low-amplitude, high-frequency activity resembling wakefulness.
• Despite the wake-like electroencephalogram, awakening from this stage requires relatively strong sensory stimulation.
• This combination of active brain waves and reduced responsiveness gives rise to the term paradoxical sleep.

Features of Paradoxical Sleep

• Rapid, conjugate eye movements occur beneath the closed eyelids.
• For this reason, paradoxical sleep is also known as rapid eye movement sleep.
• Characteristic ponto-geniculo-occipital spikes appear during this stage.
• These electrical discharges originate in the pons and propagate through the lateral geniculate nucleus to the occipital cortex.
• Rapid eye movement sleep is closely associated with vivid dreaming.
• Dreams experienced during this stage are usually detailed and are more easily remembered after awakening.
• The autonomic nervous system becomes more active during rapid eye movement sleep.
• Heart rate, blood pressure, and respiratory rate become variable and may increase intermittently.
• Respiration often becomes irregular because of fluctuations in autonomic activity.
• Penile erection commonly occurs during rapid eye movement sleep in healthy males and reflects normal autonomic function.
• Assessment of nocturnal penile tumescence may help distinguish psychogenic from organic erectile dysfunction.
• A prominent feature of rapid eye movement sleep is marked skeletal muscle atonia.
• This muscle inhibition prevents most voluntary body movements during dreaming.
• The extraocular muscles remain active to produce rapid eye movements.
• Respiratory muscles and middle ear muscles are also spared from complete paralysis.
• Muscle atonia is produced by active inhibition of spinal motor neurons through brainstem pathways.
• Stretch reflexes are markedly suppressed during this stage.
• Rapid eye movement sleep is important for emotional regulation, memory processing, learning, and normal brain development.
• Recurrent alternation between non-rapid eye movement sleep and rapid eye movement sleep is essential for healthy sleep architecture and optimal neurological function.

Mechanisms for Paradoxical Sleep

Neural Mechanisms

• Rapid eye movement sleep is generated primarily by neuronal circuits within the pontine reticular formation.
• Brain imaging studies show increased activity in the pons, amygdala, and cingulate cortex during this sleep stage.
• The characteristic rapid eye movements are initiated by ponto-geniculo-occipital spikes arising from the pons.
• These signals spread to visual pathways and contribute to the physiological features of rapid eye movement sleep.

Chemical Mechanisms

• Acetylcholine plays a major role in initiating and maintaining rapid eye movement sleep.
• Increased cholinergic activity promotes cortical activation and prolongs rapid eye movement sleep.
• Monoaminergic neurotransmitters, including serotonin and noradrenaline, generally show reduced activity during this stage.
• The interaction between cholinergic and monoaminergic systems regulates transitions between sleep stages.
• Drugs that suppress cholinergic transmission reduce rapid eye movement sleep.
• Many sedative medications, including barbiturates, decrease the duration of rapid eye movement sleep and alter normal sleep architecture.

Effect of Age on Sleep

• Sleep patterns change progressively with advancing age.
• Newborns and infants usually sleep 18–20 hours daily, with approximately 50% of sleep occurring as rapid eye movement sleep.

Functions of Sleep

• The duration of rapid eye movement sleep and deep slow-wave sleep gradually decreases during adulthood and aging.
• Adequate sleep is essential for maintaining normal physical and mental health.
• Sleep restores energy stores and promotes recovery of the brain and body.
• It improves attention, concentration, decision-making, and overall cognitive performance.
• Sleep plays a vital role in learning, memory consolidation, and long-term information retention.
• Increased growth hormone secretion during deep non-rapid eye movement sleep supports tissue growth and repair.
• Dreaming occurs predominantly during rapid eye movement sleep and contributes to normal brain function and emotional processing.
• Chronic sleep deprivation impairs physical performance, cognitive function, mood, and metabolic health.

Theories of Sleep

Sleep-Wake Cycle

• The sleep–wake cycle is a rhythmic alternation between wakefulness and sleep that follows a predictable daily pattern.
• This cycle is synchronized with the environmental light–dark cycle and is regulated by circadian mechanisms.
• Sleep results from coordinated interactions between neural circuits, neurotransmitters, and circadian signals.
• Several physiological mechanisms have been proposed to explain sleep regulation.
• Important concepts include the roles of the circadian rhythm, pineal gland, thalamocortical networks, and neurochemical modulation.

Circadian Rhythm

• The suprachiasmatic nucleus of the hypothalamus functions as the body’s biological clock.
• It is located immediately above the optic chiasm and generates endogenous circadian rhythms.
• Light information from the retina reaches the suprachiasmatic nucleus through the retinohypothalamic tract.
• This pathway synchronizes internal biological rhythms with the external day–night cycle.
• Exposure to bright light during daytime reinforces normal circadian timing.
• Bright light during the evening delays the onset of sleep by shifting the circadian clock.
• Early morning light advances the circadian rhythm and promotes earlier sleep onset on the following night.
• Reduced retinal light input after sunset decreases stimulation of the suprachiasmatic nucleus.
• This change facilitates activation of sleep-promoting pathways and supports sleep initiation.
• The suprachiasmatic nucleus coordinates neural and hormonal signals that regulate daily variations in sleep and wakefulness.
• It also synchronizes other physiological rhythms, including body temperature, hormone secretion, and metabolism.
• The pineal gland contributes to circadian regulation by secreting melatonin, particularly during darkness.
• Melatonin promotes sleep by signaling the onset of the biological night.
• Thalamocortical circuits generate synchronized electrical activity characteristic of non-rapid eye movement sleep.
• Changes in neurotransmitters, including acetylcholine, serotonin, noradrenaline, histamine, and adenosine, regulate transitions between wakefulness and different sleep stages.
• Balanced interaction among these neural systems maintains normal sleep architecture.
• Circadian timing differs among species because some animals are predominantly active during the day, whereas others are active at night.
• In humans, proper alignment of the circadian rhythm with the light–dark cycle is essential for healthy sleep, cognitive performance, and overall physiological function.

Role of Pineal Gland

• The pineal gland is an important neuroendocrine organ involved in regulation of the circadian rhythm and sleep.
• It functions in close association with the hypothalamic suprachiasmatic nucleus, the body’s biological clock.
• Light information reaches the suprachiasmatic nucleus through the retinohypothalamic pathway.
• Circadian signals are transmitted through sympathetic pathways to the pineal gland.
• Sympathetic nerve terminals release noradrenaline, which stimulates melatonin synthesis by pinealocytes.
• Melatonin secretion increases during darkness and decreases with exposure to light.
• Plasma melatonin levels are highest during the evening and early part of the night.
• Melatonin acts on specific receptors within the brain to promote sleep and synchronize the sleep–wake cycle.
• It also helps coordinate circadian rhythms of hormone secretion, body temperature, and other physiological functions.
• Melatonin receptors are classified mainly as MT1 and MT2, which mediate its physiological actions.
• Normal melatonin secretion depends on an intact retina, hypothalamus, sympathetic pathway, and pineal gland.
• Disruption of this pathway may contribute to circadian rhythm disorders, insomnia, and sleep disturbances.
• The pineal gland is relatively larger during infancy and gradually undergoes age-related involution.

Role of Thalamocortical Loop

• The thalamocortical loop is an important neural network regulating the sleep–wake cycle.
• Reciprocal connections between the thalamus and cerebral cortex generate rhythmic electrical activity.
• Thalamic reticular neurons synchronize cortical activity during sleep.
• During wakefulness, thalamocortical neurons produce high-frequency, low-amplitude electrical activity.
• During sleep, neuronal firing becomes slower and more synchronized, generating characteristic sleep rhythms.
• Gamma oscillations are associated with sensory processing, attention, and cortical integration during wakefulness.
• Coordinated thalamocortical activity enables normal transitions between wakefulness and different sleep stages.

Role of Neurochemicals in Brainstem

• The sleep–wake cycle is regulated by interactions among several brainstem and hypothalamic neurotransmitters.
• Neurons of the reticular activating system release noradrenaline, serotonin, and acetylcholine to modulate cortical activity.
• Noradrenaline from the locus coeruleus and serotonin from the raphe nuclei promote wakefulness and help regulate transitions between sleep stages.
• Acetylcholine increases cortical activation and is most active during wakefulness and rapid eye movement sleep.
• Reduced activity of noradrenergic and serotonergic neurons facilitates the onset of rapid eye movement sleep.
• In the hypothalamus, histamine released from the tuberomammillary nucleus promotes alertness and wakefulness.
• Gamma-aminobutyric acid released from neurons in the preoptic area inhibits wake-promoting centers and facilitates sleep onset.
• Balanced interactions among acetylcholine, noradrenaline, serotonin, histamine, and gamma-aminobutyric acid maintain normal sleep architecture and regulate transitions between wakefulness, non-rapid eye movement sleep, and rapid eye movement sleep.

Clinical Usage of EEG

Diagnosis of Various Types of Epilepsies

• Electroencephalography is an important, noninvasive investigation for assessing abnormal electrical activity of the brain.
• It is widely used in the diagnosis of epilepsy, sleep disorders, and other neurological conditions.
• Epilepsy is characterized by recurrent seizures caused by excessive, synchronized neuronal discharges within the cerebral cortex.
• During a seizure, the electroencephalogram records characteristic abnormal waveforms that help identify the type of epilepsy.
• Generalized seizures involve both cerebral hemispheres and are usually associated with impaired consciousness.
• Generalized tonic–clonic seizures show widespread abnormal electrical activity with characteristic changes during the tonic and clonic phases.
• Absence seizures produce brief episodes of impaired awareness with minimal motor activity.
• Their electroencephalogram typically demonstrates generalized 3-hertz spike-and-wave complexes.
• Focal seizures originate from a localized cortical region, and electroencephalogram findings help identify the epileptogenic focus.
• The clinical manifestations of focal seizures depend on the affected cortical area.
• A normal electroencephalogram between seizures does not exclude a diagnosis of epilepsy.

Intracranial Space Occupying Lesion

• Brain tumors usually alter electroencephalogram activity indirectly by compressing or disrupting adjacent cortical neurons.
• Such lesions may produce focal slowing or other localized abnormalities that help identify the affected cerebral region.
• Subdural hematoma and other intracranial collections can similarly produce localized electroencephalogram changes.

Diagnosis of Sleep Disturbances

• Electroencephalography is an essential component of sleep evaluation.
• Characteristic brain wave patterns distinguish normal sleep stages and identify abnormalities in sleep architecture.
• It is commonly combined with other physiological recordings in polysomnography to investigate sleep disorders.
• Interpretation of electroencephalogram findings should always be integrated with clinical history, neurological examination, and neuroimaging when appropriate.

Sleep Disorders

• Sleep disorders are disturbances in the quality, timing, or regulation of normal sleep.
• Different disorders occur preferentially during non-rapid eye movement sleep or rapid eye movement sleep.
• Sleepwalking, night terrors, and nocturnal enuresis are commonly associated with deep non-rapid eye movement sleep.
• Bruxism and rapid eye movement sleep behavior disorder are more commonly related to rapid eye movement sleep.

Insomnia

• Insomnia is the persistent inability to initiate or maintain adequate sleep despite sufficient opportunity for sleep.
• Primary insomnia occurs without an identifiable medical cause.
• Secondary insomnia develops because of medical illnesses, psychiatric disorders, medications, or substance use.
• Chronic insomnia impairs daytime alertness, memory, mood, and cognitive performance.

Narcolepsy

• Narcolepsy is a neurological disorder characterized by excessive daytime sleepiness and sudden episodes of sleep.
• Rapid eye movement sleep may occur soon after sleep onset, unlike the normal sleep sequence.
• Many patients experience cataplexy, which is a sudden, brief loss of muscle tone triggered by strong emotions while consciousness is preserved.
• Some individuals also experience transient sleep paralysis at sleep onset or upon awakening.
• Narcolepsy is strongly associated with reduced orexin (hypocretin) production by neurons of the lateral hypothalamus.

Bruxism

• Bruxism is involuntary grinding or clenching of the teeth during sleep.
• It is caused by repetitive contractions of the jaw muscles and may result in tooth wear, jaw pain, and temporomandibular joint dysfunction.

Nocturnal Enuresis

• Nocturnal enuresis is involuntary urination during sleep after the age at which bladder control is normally expected.
• It is more common in children and usually improves with age.
• Episodes typically occur during deep non-rapid eye movement sleep in the early part of the night.
• Delayed maturation of bladder control mechanisms, nocturnal polyuria, and impaired arousal contribute to this condition.
• Evaluation of persistent sleep disorders may require polysomnography, clinical assessment, and appropriate neurological or psychiatric investigations.
• Early recognition and treatment improve sleep quality, daytime function, and overall health.

Parasomnic Disturbances

• Parasomnias are a group of sleep disorders characterized by abnormal movements, behaviors, emotions, or sensory experiences that occur exclusively or predominantly during sleep or during transitions between sleep and wakefulness.
• These disorders usually arise during non-rapid eye movement sleep, rapid eye movement sleep, or the transition between sleep and wakefulness.
• Common parasomnias include sleep starts, sensory paroxysms, nocturnal paroxysmal dystonia, sleep paralysis, night terrors, nightmares, sleepwalking, and rapid eye movement sleep behavior disorder.

Somnolescent Starts

• Sleep starts are sudden, brief involuntary muscle jerks that occur at the onset of sleep or during the early stages of non-rapid eye movement sleep.
• These movements commonly involve one or both legs or the trunk, while the upper limbs are affected less frequently.
• Some individuals experience a sensation of falling or other vivid sensory perceptions at the same time.
• Sleep starts are benign and should be distinguished from nocturnal epilepsy and other seizure disorders.

Sensory Paroxysms

• Sensory paroxysms consist of sudden abnormal sensory experiences that occur during sleep.
• Affected individuals may awaken with the sensation that an unusual feeling is spreading throughout the body.
• Common experiences include bright flashes of light, loud crashing sounds, or sensations of spinning, floating, or being lifted.
• These episodes are often associated with transient dysfunction of the vestibular system, which is responsible for balance and spatial orientation.

Nocturnal Paroxysmal Dystonia

• Nocturnal paroxysmal dystonia is characterized by sudden episodes of abnormal involuntary movements during non-rapid eye movement sleep.
• The movements may include dystonic, choreiform, or ballistic patterns involving different parts of the body.
• Individuals may appear awake with fearful facial expressions despite remaining asleep.
• The disorder can occur at any age and affects both males and females.

Sleep Paralysis

• Sleep paralysis is a temporary inability to perform voluntary muscle movements during the transition between sleep and wakefulness.
• It most commonly occurs at the end of rapid eye movement sleep when normal muscle paralysis persists briefly after awakening.
• Eye movements and respiratory muscle function remain intact during the episode.
• Consciousness is preserved, and the condition usually resolves spontaneously within a few seconds to minutes.

Night Terrors and Nightmares

• Night terrors occur predominantly in children and usually arise during deep non-rapid eye movement sleep, particularly in the first third of the night.
• The affected individual suddenly awakens with intense fear, rapid heart rate, rapid breathing, and marked autonomic activation.
• Episodes generally last one to two minutes, after which the individual returns to sleep.
• Most children have little or no memory of the event on awakening.
• Nightmares are disturbing dreams that occur during rapid eye movement sleep and are usually remembered after awakening.

Somnambulism

• Sleepwalking is characterized by walking or performing complex activities while remaining asleep.
• The individual may sit up, leave the bed, walk with the eyes open, or perform simple routine activities without conscious awareness.
• Sleepwalking usually occurs during deep non-rapid eye movement sleep in the first third of the night.
• Individuals typically do not respond appropriately to external stimuli during an episode.
• Complete amnesia for the event is common after awakening.
• Sleepwalking is usually benign in children but may occasionally result in injury or complex behaviors in adults.

REM Sleep Behavior Disorder

• Rapid eye movement sleep behavior disorder is characterized by vigorous motor activity during rapid eye movement sleep.
• The normal muscle paralysis of rapid eye movement sleep is absent, allowing individuals to physically act out vivid dreams.
• Behaviors may include shouting, punching, kicking, or other forceful movements.
• The disorder is more common in older adults and may cause injury to the affected individual or the bed partner.
• Early recognition is important because this disorder may be associated with underlying neurodegenerative diseases.

Obstructive Sleep Apnea

• Obstructive sleep apnea is a common sleep disorder that occurs mainly in middle-aged and older adults, although it can affect individuals of any age.
• The disorder is characterized by repeated episodes of complete or partial upper airway obstruction during sleep.
• Each episode of apnea or marked reduction in airflow usually lasts 10 seconds or longer despite continued respiratory effort.
• Relaxation of the pharyngeal muscles during sleep narrows or blocks the upper airway.
• Sleep becomes fragmented because each episode is terminated by brief arousal, which restores airway patency.
• Stage 1 non-rapid eye movement sleep increases, whereas deep non-rapid eye movement sleep is significantly reduced.
• Recurrent sleep disruption decreases overall sleep quality and reduces restorative sleep.
• Common manifestations include loud snoring, witnessed apneic episodes, excessive daytime sleepiness, morning headache, impaired concentration, and fatigue.
• Untreated obstructive sleep apnea increases the risk of hypertension, cardiovascular disease, stroke, metabolic disorders, and road traffic accidents.

Hypersomnia (Excessive Sleep)

• Hypersomnia is characterized by excessive sleep duration or persistent daytime sleepiness despite apparently adequate sleep.
• It may result from disorders affecting the brainstem reticular activating system, hypothalamus, or other sleep-regulating neural pathways.
• Damage to these regions can disturb the normal balance between sleep-promoting and wake-promoting mechanisms.
• Hypersomnia differs from excessive sleep caused by infections, medication use, or sleep deprivation.
• Appropriate evaluation is essential to identify the underlying neurological or systemic cause and to guide treatment.