Glossary

1. Canonical physiological sleep states according to polysomnography

“Light Sleep”

•Stage 1: closed eyes, slow eye-rolling movements, EEG alpha waves (8–12 Hz) subside, slower theta waves (4–8 Hz) arrive.

•Stage 2: eye movements cease, 12–14 Hz bursts (sleep spindles) and brief high voltage waves (K-complexes) occur. “Deep Sleep” or “Slow-Wave Sleep”

•Stage 3: a mixture of sleep spindles and high-amplitude, slow frequency delta waves (0.5–4 Hz).

•Stage 4: delta waves almost exclusively.

•REM (Rapid Eye Movement) or “Paradoxical Sleep”: fast-frequency, low-amplitude waves, limb muscles paralyzed, eyes closed with rapid eye movements.

2. Phenomenological sleep terms

•Sleep mentation: sleep thoughts and images.

•Dreaming: immersion in the imagined dreamworld; “immersive spatiotemporal hallucination” (Windt 2010).

•Lucid Dreaming: knowing that one is dreaming while dreaming; being able to direct one’s attention to the dream as a dream (Windt & Metzinger 2007).

•Dreamless sleep (Western conception): sleep lacking mentation.

•Dreamless sleep (Indian conception): sleep lacking mentation; phenomenal character of peaceful, non-intentional awareness.

•Lucid dreamless sleep (Indian conception): sleep lacking mentation; phenomenal character of peaceful, non-intentional awareness; non-conceptual meta-awareness (“witness consciousness”) of the dreamless sleep state.

Glossary of Indian philosophical systems

CONSCIOUSNESS IN DREAMLESS SLEEP
Yoga	•Yoga Sūtras, traditionally ascribed to Patañjali, though authorship is uncertain (c. 3^rd–4^th century CE). The commentary attributed to Vyāsa may in fact have been written by Patañjali.
Advaita Vedānta (Advaitins)	•Śaṇkara (788–820 CE). •Sureśvara (c. 9^th century CE). •Madhusūdana (c. 16^th century CE).
Buddhism	•The Theravāda school postulates a basal and passive “life continuum” or “factor of existence” consciousness (bhavaṅga) that occurs in dreamless sleep (c. 3^rd century BCE–2^nd century CE). •The Yogācāra school postulates a basal “store consciousness” (ālaya-vijñāna), which persists in dreamless sleep (c. 4^th century CE).
NO CONSCIOUSNESS IN DREAMLESS SLEEP
Nyāya (Nyaiyāyikas)	•Nyāya Sūtras, authored by Gautama (c. 2^nd century BCE). •Vātsyāyana (c. 450 CE). Udyotakara (c. 550 CE ). •Udayana (c. 10^th century CE).