The period marks a shift toward a circadian-centered understanding of sleep, integrating internal pacemakers with environmental cues to explain timing, sleep architecture, and dream phenomenology. The discovery of melatonin as a pineal regulator and the delineation of exogenous versus endogenous influences fostered a unified framework for circadian biology and sleep research, while laboratory studies highlighted how context shapes sleep measurements. Historical Significance: These breakthroughs established the circadian paradigm as the organizing principle of sleep research, catalyzing cross-species clock studies and the development of chronobiology as a field. They informed methodological standards and spurred subsequent explorations into sleep architecture, dream theory, and pineal biology, guiding decades of pharmacological and therapeutic work.