Lec 3 Sleep Disorders and Neuropsychology PDF

Sleep disorders and Neuropsychology Dr. Amna Aurooj In neuroscience, the sleep cycle is a complex and crucial process that involves different stages of sleep, regulated by neural and physiological mechanisms. Understanding the sleep cycle from a neuroscience perspective requires exploring the brain...

Sleep disorders and Neuropsychology Dr. Amna Aurooj In neuroscience, the sleep cycle is a complex and crucial process that involves different stages of sleep, regulated by neural and physiological mechanisms. Understanding the sleep cycle from a neuroscience perspective requires exploring the brain structures, neurochemicals, and processes involved in transitioning through different sleep stages. 1. Sleep Stages: The sleep cycle consists of Non-Rapid Eye Movement (NREM) sleep and Rapid Eye Movement (REM) sleep. These two states alternate in cycles throughout the night. a) NREM Sleep:  Stage 1 (N1): This is the transition stage between wakefulness and sleep. It is a light sleep stage where the brain produces theta waves (3-8 Hz). People in this stage may experience hypnagogic hallucinations or sudden muscle contractions (hypnic jerks).  Stage 2 (N2): A deeper stage of light sleep, marked by sleep spindles (sudden bursts of brain activity) and K-complexes (high-amplitude waves). This stage occupies about 50% of the sleep cycle.  Stage 3 (N3): Also known as deep sleep or slow-wave sleep (SWS), this stage is characterized by delta waves (0.5-4 Hz), which are large, slow brain waves. This stage is crucial for restorative functions such as tissue growth and repair, immune function, and memory consolidation. b) REM Sleep:  REM sleep is the stage where most vivid dreams occur. It is marked by rapid movement of the eyes, low muscle tone (atonia), and brain activity that resembles wakefulness, with beta waves (12-30 Hz). This stage is associated with learning, memory, and emotional regulation.  REM sleep occupies about 20-25% of the sleep cycle in adults and typically occurs 90 minutes after falling asleep, repeating multiple times during the night. 2. Sleep Cycle Dynamics:  The sleep cycle lasts about 90 minutes on average, with NREM and REM alternating in a regular pattern. A typical night’s sleep consists of 4 to 6 sleep cycles, with more deep  sleep (NREM stage 3) occurring in the first half of the night and longer REM stages later in the night.  Sleep architecture changes throughout the lifespan, with infants having more REM sleep, while older adults experience shorter sleep cycles with fewer deep sleep stages. 3. Neuroscience of Sleep: Sleep is regulated by several brain regions and neurochemicals: a) Brain Regions:  Suprachiasmatic Nucleus (SCN): Located in the hypothalamus, the SCN serves as the body's biological clock or circadian pacemaker, regulating the sleep-wake cycle based on light-dark cues. The SCN controls melatonin release from the pineal gland and orchestrates sleep timing.  Hypothalamus: It plays a crucial role in regulating sleep through the release of sleep- promoting substances (e.g., GABA) and the activation of sleep-inducing brain areas.  Reticular Activating System (RAS): A network in the brainstem that regulates wakefulness and arousal. The RAS promotes wakefulness when activated, whereas its suppression facilitates sleep.  Thalamus: During NREM sleep, the thalamus blocks sensory information from reaching the cortex, allowing the brain to focus on internal processes rather than external stimuli.  Amygdala: Active during REM sleep, the amygdala is involved in processing emotions and may contribute to emotional regulation through dreaming. b) Neurotransmitters:  GABA (Gamma-Aminobutyric Acid): An inhibitory neurotransmitter that reduces neuronal activity and plays a key role in initiating sleep and maintaining NREM sleep.  Adenosine: A byproduct of energy consumption, adenosine builds up in the brain during wakefulness and promotes sleep by inhibiting wake-promoting neurons.  Melatonin: Produced by the pineal gland, melatonin is a hormone that signals the onset of sleep and regulates the circadian rhythm.  Orexin (Hypocretin): Produced in the hypothalamus, orexin promotes wakefulness and prevents transitions to REM sleep. Dysfunction in orexin signaling is linked to narcolepsy.   Acetylcholine: High levels of acetylcholine are present during REM sleep, facilitating dream-related brain activity and memory processing.  Serotonin and Norepinephrine: Both neurotransmitters are active during wakefulness but suppressed during REM sleep, affecting mood and alertness. 4. Sleep Disorders: Disruptions to normal sleep patterns or the sleep cycle can lead to a variety of sleep disorders, which have important neurological implications:  Parasomnias: Disorders that involve abnormal behaviors during sleep, such as sleepwalking, night terrors, sleep paralysis. These can lead to injury and sleep disruption, impacting cognitive performance and emotional stability.  Circadian Rhythm Disorders: These disorders affect the timing of sleep, often leading to difficulties falling asleep or waking up at socially appropriate times. Jet lag, shift work disorder, and delayed sleep phase syndrome are examples, often resulting in cognitive impairment and mood disturbances.  Insomnia: Difficulty falling asleep, staying asleep, or waking up too early. Chronic insomnia can lead to cognitive impairments, such as difficulties with attention, memory, and executive functioning.  Sleep Apnea: Characterized by repeated interruptions in breathing during sleep, often due to airway obstruction (obstructive sleep apnea) or a central nervous system issue (central sleep apnea), leading to frequent awakenings and decreased REM and deep sleep. It leads to fragmented sleep, excessive daytime sleepiness, and cognitive deficits, particularly in attention and memory.