Conférences CRNL Christian Cajochen "Tuned to Time: How Rhythms and Light Modulate Melatonin Secretion, Sleep and Dream Recall"

Astract

Human sleep and wakefulness are shaped by interacting circadian and ultradian rhythms, homeostatic sleep pressure, and environmental influences operating across different timescales. This talk will explore how these processes regulate circadian physiology, sleep propensity and dreaming.

The first part will focus on the non-visual effects of light, mediated primarily by intrinsically photosensitive retinal ganglion cells, on melatonin rhythms and sleep onset latency. Evidence will highlight seasonal variation in these responses, even under controlled laboratory conditions. The second part will draw on ultrashort sleep-wake protocols to examine how the circadian system promotes wakefulness and sleep, with particular emphasis on REM sleep and dream recall. EEG features associated with successful dream recall will be discussed alongside differences in the emotional content of dreams recalled after NREM and REM awakenings, including findings in women with major depression.

Finally, emerging evidence for possible lunar modulation of human sleep will be critically considered, acknowledging the uncertainties surrounding this debated topic. Together, these findings illustrate how internal regulatory processes and environmental cycles shape both the physiology and subjective experience of sleep.