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Biological Rhythms

Patterns of physiological changes that are driven by internal biological clocks, with typical free-running periods of approximately $\tau \rightarrow 24.2$ hours.

Zeitgebers

Environmental cues, such as light, that help synchronize biological rhythms to the solar day.

Suprachiasmatic Nucleus (SCN)

The master circadian pacemaker located in the anterior hypothalamus, regulating circadian rhythms.

Melanopsin

A photopigment found in intrinsically photosensitive retinal ganglion cells that mediates non-image-forming photoreception.

Electroencephalography (EEG)

A technique used to measure electrical activity in the brain during sleep.

Slow-Wave Sleep (N3)

A deep stage of sleep characterized by delta waves, associated with growth hormone secretion.

Two-Process Model

A model proposed by Alexander Borbély describing the regulation of sleep through homeostatic (Process S) and circadian (Process C) processes.

Insomnia Disorder

A sleep disorder characterized by difficulty falling asleep or staying asleep, often treated with cognitive behavioral therapy (CBT-I).

Narcolepsy Type 1

A sleep disorder caused by the loss of orexin/hypocretin neurons, leading to excessive daytime sleepiness and cataplexy.

Obstructive Sleep Apnea (OSA)

A condition marked by repeated upper airway collapse during sleep, resulting in disrupted sleep and other health issues.

Ultradian Rhythms

Biological cycles occurring in less than 24 hours, such as cycles of sleep stages.

Infradian Rhythms

Biological cycles occurring over more than 24 hours, such as the menstrual cycle or seasonal affective disorder.

Activation-Synthesis Hypothesis

A theory of dreaming suggesting that dreams result from the brain's attempt to make sense of neural activity during sleep.