Chapter 59: States of Brain Activity—Sleep, Brain Waves, Epilepsy, Psychoses

 

To read more check out Chapter  43:

https://mednotesbyrazaullah.blogspot.com/2026/09/chapter-43-aviation-high-altitude-and.html

Sleep States and Types

Brain activity fluctuates through distinct states such as wakefulness, sleep, extreme excitement, and various mood levels driven by internal activating or inhibiting forces. Sleep is specifically defined as a state of reversible unconsciousness from which a person can be aroused by sensory or other stimuli, distinguishing it entirely from permanent coma. Normal sleep cycles alternate between two completely different types: slow-wave sleep and rapid eye movement (REM) sleep.  

Slow-wave sleep constitutes the deep, highly restful sleep experienced during the first hour after prolonged wakefulness, characterized by reduced metabolic rate, blood pressure, and muscle tone. REM sleep accounts for roughly 25 percent of sleep time in young adults, recurring every 90 minutes in association with vivid dreaming, high brain metabolism, and active desynchronized EEG patterns resembling wakefulness.  

Mechanisms and Physiological Functions of Sleep

Sleep is driven by active inhibitory brain centers rather than mere passive fatigue of the reticular activating system. The midline raphe nuclei in the lower pons and medulla secrete serotonin to promote sleep, while experimental lesions in these areas induce intense, fatal wakefulness. Additional sleep-promoting regions include the nucleus of the tractus solitarius and the rostral hypothalamus.  

• Slow-wave sleep produces deep rest with decreased blood pressure.  
• REM sleep exhibits desynchronized brain waves and active dreaming.  
• Raphe nuclei neurons secrete serotonin to promote sleep states.  
• Serotonin synthesis blockers prevent sleep for several days.  
• Cerebrospinal fluid of sleep-deprived animals contains active sleep peptides.  
• Brain acetylcholine neurons trigger periodic episodes of REM sleep.  
• Sleep deprivation progressively degrades cognitive and physical performance.  
• Sleep restores neural balance among overactive central nervous system centers.  

Electroencephalogram (EEG) and Brain Wave Patterns

Continuous electrical activity recorded from the scalp generates an electroencephalogram (EEG), reflecting the synchronous firing of millions of underlying cortical neurons. Healthy individuals display four primary types of brain waves categorized by frequency and voltage ranges during different behavioral and cognitive states.  

• Alpha waves show 8 to 13 cycles per second in resting adults.  
• Opening eyes replaces alpha waves with desynchronized beta waves.  
• Beta waves exceed 14 cycles per second during mental activity.  
• Theta waves range from 4 to 7 cycles per second normally.  
• Delta waves drop below 3.5 cycles during deep sleep or coma.  
• Thalamocortical feedback circuits generate synchronized alpha wave oscillations.  
• Cortical networks can sustain delta waves independently of lower structures.  
• EEG progression tracks sleep stages from light spindles to delta waves.  

Clinical Epileptic Seizures and Discharge Patterns

Epilepsy involves uncontrolled, excessive electrical discharges originating from hypersensitive neuronal circuitry within the central nervous system. Clinical classifications divide epileptic events into grand mal attacks affecting the entire brain, petit mal absence syndromes involving the thalamocortical system, and focal seizures emerging from localized structural lesions.  

• Grand mal seizures cause generalized tonic-clonic muscle spasms and stupor.  
• High-voltage, high-frequency synchronous discharges mark grand mal EEG traces.  
• Neuronal fatigue and active inhibition terminate grand mal episodes.  
• Petit mal epilepsy produces brief 3 to 30 second unconsciousness.  
• Spike and dome EEG patterns characterize petit mal absence seizures.  
• Focal epilepsy arises from local scar tissue, tumors, or trauma.  
• Jacksonian epilepsy manifests as a progressive march of muscle contractions.  
• Psychomotor seizures involve limbic structures and cause transient behavioral amnesia.  

Neurotransmitter Imbalances in Psychoses and Mood Disorders

Many psychiatric conditions and neurodegenerative dementias stem from localized functional abnormalities or diminished activities within specific monoaminergic and amino acid neurotransmitter systems. Pharmacological agents targeting these chemical pathways successfully manage diverse behavioral symptoms and cognitive disturbances.  

• Mental depression correlates with reduced brain norepinephrine and serotonin activity.  
• Tricyclic antidepressants block monoamine reuptake to prolong neurotransmitter action.  
• Monoamine oxidase inhibitors prevent neurotransmitter destruction to relieve depression.  
• Lithium salts effectively treat the manic phase of bipolar disorders.  
• Schizophrenia involves prefrontal glutamate dysfunction and mesolimbic dopamine excess.  
• Antipsychotic drugs decrease dopamine secretion or postsynaptic receptor effects.  
• Hippocampal shrinkage frequently accompanies chronic schizophrenic brain pathology.  
• Electroconvulsive therapy enhances central norepinephrine transmission to counter depression.  

Alzheimer’s Disease and Neurodegenerative Pathology

Alzheimer’s disease is a progressive, fatal neurodegenerative disorder characterized by premature brain aging, severe amnesic memory impairment, language deterioration, and visuospatial deficits. Pathologically, the disease involves widespread neuronal loss within limbic memory pathways and the abnormal accumulation of beta-amyloid peptides forming extracellular amyloid plaques throughout the neocortex, hippocampus, and subcortical structures.  

• Alzheimer’s disease represents the most common form of dementia.  
• Prevalence doubles approximately every 5 years past age 60.  
• Beta-amyloid peptide accumulates extensively into characteristic cerebral amyloid plaques.  
• Genetic mutations linked to the disease increase beta-amyloid production.  
• Trisomy 21 patients develop Alzheimer neuropathology by midlife.  
• Apolipoprotein E gene variations accelerate amyloid deposition risks.  
• Transgenic animal models overexpressing amyloid display learning deficits.  
• Hypertension and cerebrovascular disease exacerbate cognitive decline in Alzheimer patients.