Brain Electrical Activity, Sleep Stages, and Epilepsy

Comprehensive vocabulary flashcards covering brain electrical rhythms (EEG waveforms), physiological origins, sleep stages, sleep regulatory centers and disorders, and clinical classification of epilepsy and seizures.

Electroencephalogram (EEG)

A noninvasive recording technique using scalp electrodes that detects small electrical voltage differences over time generated by brain activity.

Physiological Origin of EEG Waves

Primarily the summed excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) occurring in aligned cortical pyramidal neurons, rather than individual action potentials.

Neuronal Synchrony (EEG Detection)

The coordinated simultaneous activity of large populations of aligned cortical neurons necessary to produce electrical signals large enough to conduct through the skull and scalp.

Delta Waves

Slow EEG brain waves with a frequency of $0.5\text{--}4\,\text{Hz}$ that originate in cortical neurons and predominate during deep NREM sleep (stage N3).

Theta Waves

EEG rhythms with a frequency of $4\text{--}8\,\text{Hz}$, characteristically observed during drowsiness, light sleep, and daydreaming.

Alpha Waves

EEG rhythms with a frequency of $8\text{--}13\,\text{Hz}$ associated with relaxed wakefulness with eyes closed (posterior alpha rhythm); they disappear if cortical connections to the thalamus are transected.

Beta Waves

Low-amplitude, fast EEG brain waves with a frequency of $13\text{--}30\,\text{Hz}$ reflecting an alert, aroused brain engaged in active mental cognition or task performance.

Polysomnography

A diagnostic sleep study combining EEG with recordings of eye movements, muscle tone, and other physiological signals to identify sleep architecture, stages, and disorders.

Sleep

A reversible state of unconsciousness from which an individual can be aroused by sensory or other environmental stimuli.

Non-REM (NREM) Sleep

Restorative, slow-wave quiet sleep comprising approximately $75\text{--}80\%$ of a typical night, divided into stages N1, N2, and N3, with concurrent reductions in blood pressure, heart rate, and basal metabolism.

Sleep Spindles and K-complexes

Distinctive episodic EEG waveforms that characterize stage N2 of non-rapid eye movement (NREM) sleep.

Stage N3 Sleep

The deepest slow-wave stage of NREM sleep, characterized by prominent delta waves, reduced autonomic activity, and essential support for physical restoration.

REM (Rapid Eye Movement) Sleep

Active or paradoxical sleep making up $20\text{--}25\%$ of sleep that recurs roughly every $90\,\text{min}$, featuring low-amplitude mixed-frequency EEG activity, rapid eye movements, profound skeletal muscle atonia, and vivid dreaming.

Raphe Nuclei

Serotonergic neuronal clusters in the brainstem responsible for the genesis and maintenance of slow-wave (NREM) sleep.

Locus Coeruleus

A noradrenergic nucleus situated beneath the floor of the fourth ventricle within the brainstem reticular formation that participates in regulating REM sleep and wakefulness.

Circadian Rhythm

An endogenous, natural biological cycle that repeats approximately every $24\,\text{hours}$ to synchronize sleep-wake patterns and hormonal fluctuations with environmental light-dark changes.

Suprachiasmatic Nucleus (SCN)

The primary master circadian clock located in the hypothalamus that receives photic input via the retino-hypothalamic tract to orchestrate circadian timing and suppress daytime melatonin release.

Melatonin

An endocrine hormone synthesized from tryptophan by pinealocytes in the pineal gland; its production is suppressed by sunlight, rises during the evening, and peaks in the middle of the night.

$MT_1$ and $MT_2$ Receptors

G-protein-coupled receptors located on SCN neurons and peripheral cells through which melatonin and $MT_1$ agonists act to promote sleep and regulate the circadian sleep-wake cycle.

Orexin (Hypocretin)

A hypothalamic neuropeptide secreted by lateral hypothalamic neurons that stabilizes wakefulness and prevents inappropriate, sudden intrusions of REM sleep.

Somnambulism (Sleepwalking)

An NREM parasomnia characterized by incomplete arousal from stage N3 deep sleep during the first third of the night, leading to motor ambulation with diminished consciousness and subsequent amnesia.

Narcolepsy (Gelineau's Syndrome)

A central disorder of hypersomnolence caused by deficient hypothalamic orexin signaling, marked by excessive daytime sleepiness, cataplexy, sleep paralysis, and vivid hypnagogic or hypnopompic hallucinations.

Cataplexy

An emotion-triggered, abrupt loss of voluntary muscle tone characteristic of type 1 narcolepsy, caused by the abnormal intrusion of REM-associated muscle atonia into wakefulness.

REM Sleep Behavior Disorder (RBD)

A REM parasomnia wherein patients physically enact dreams due to a pathological failure of normal REM skeletal muscle atonia, carrying a significant risk of physical trauma.

Fatal Familial Insomnia

A rare, inherited prion disease causing progressive thalamic degeneration, gliosis, profound intractable insomnia, dementia, and death.

Epileptic Seizure

A transient clinical event resulting from abnormal, excessive, or hypersynchronous neuronal electrical discharges in the brain.

Epilepsy

A chronic neurological disorder characterized by an enduring predisposition to recurrent unprovoked seizures, typically diagnosed following $\ge 2$ unprovoked seizures occurring $>24\,\text{hours}$ apart.

Paroxysmal Depolarization Shift (PDS)

A prominent, sustained cellular depolarization of epileptogenic neurons accompanied by a burst of high-frequency action potentials and subsequent afterhyperpolarization, representing the cellular substrate of an interictal spike.

Absence Seizure (Petit Mal)

A generalized nonmotor seizure marked by brief, sudden behavioral arrests, staring spells, and immediate return of awareness, typically accompanied on EEG by classic $\sim 3\,\text{Hz}$ spike-and-wave discharges.

Temporal Lobe Seizure (Psychomotor Epilepsy)

A focal seizure arising within the temporal lobe, frequently presenting with altered awareness, automatisms, and square-wave or notched electrical patterns on EEG.

Generalized Tonic-Clonic Seizure (Grand Mal)

A major convulsive seizure presenting with sustained full-body stiffening (tonic phase) followed by rhythmic bilateral jerking (clonic phase), culminating in postictal stupor and marked EEG suppression.

Status Epilepticus

A life-threatening medical emergency defined by a continuous convulsive seizure lasting $\ge 5\,\text{minutes}$ or recurrent seizures occurring without recovery of consciousness between episodes.

Benign Rolandic Epilepsy

A common pediatric focal epilepsy syndrome that typically emerges in childhood (beginning as early as $6\,\text{months}$) and characteristically remits spontaneously between ages $5\text{--}13$.