Sleep and dreams of monks

French sleep scientists have studied a group of monks who have virtually no contact with the outside world and have taken a vow of silence.

The monks are of scientific interest owing to the tradition of having two sleep periods per night interrupted by a 2-3 hour prayer and psalm reading session.

The research group were interested in how the sleep-regulating circadian rhythm adjusts to this two sleep system.

It turns out that the automatic rising and falling of body temperature seemed to sync with the two-period sleep patterns but that the monks still had sleep problems (difficulty sleeping, waking, daytime sleepiness).

This suggests that they were not fully adjusted, even after decades of practice (the researchers report that “They all used several (two to six) alarm clocks”!)

Delightfully, the monks were also asked about their tendency to hallucinate and about the content of their dreams.

Although only ten individuals were studied, the answers are oddly appropriate for members of a silent, closed order.

Six monks had experienced mild (n = 4, ringing of the cell door at sleep offset or of the alarm clock, feeling that someone hit them briefly in the back, waking-up during the second sleep while mentally singing psalms) and moderate (n = 2, nightmarish, prolonged feeling of a demoniac presence at sleep onset after Matins) sleep-related hallucinations vs. one control (p = .06). Occasional nightmares were more frequent in monks than in controls.

All monks reported dreaming more often after than before the Matins [midnight prayers in between the two sleep periods], and to have conversations in their dreams. These conversations were rare (n = 3), hard to understand (n = 2), or frequent (n = 5). As for prayers, six monks were able to pray while dreaming, although it was rare, whereas two others dreamt of acts of piety, or imagined a disrupted liturgy, and finally two of them dreamt they were never monks.

Ring the Bell for Matins: Circadian Adaptation to Split Sleep by Cloistered Monks and Nuns 

Dec., 2011, Vol. 28, No. 10 , Pages 930-941 (doi:10.3109/07420528.2011.624436)
Isabelle Arnulf,1,2 Agnès Brion,1 Michel Pottier,1 and Jean-Louis Golmard3
1Sleep Disorders Unit, Pitié-Salpêtrière Hospital, APHP, Paris, France
2CRICM–Pierre and Marie Curie University, Inserm UMR_S 975, CNRS UMR 722, Paris, France
3Department of Biostatistics, Pitié-Salpêtrière Hospital, ER4, Pierre and Marie Curie University, Paris, France
Address correspondence to Dr. Isabelle Arnulf, Unité des Pathologies du Sommeil, Hôpital Pitié-Salpêtrière, 47–83 boulevard de l’Hôpital, 75651 Paris Cedex 13, France. Tel.: 00 33 1 42 16 77 01; Fax: 00 33 1 42 16 77 00; E-mail:

Cloistered monks and nuns adhere to a 10-century-old strict schedule with a common zeitgeber of a night split by a 2- to 3-h-long Office (Matins). The authors evaluated how the circadian core body temperature rhythm and sleep adapt in cloistered monks and nuns in two monasteries. Five monks and five nuns following the split-sleep night schedule for 5 to 46 yrs without interruption and 10 controls underwent interviews, sleep scales, and physical examination and produced a week-long sleep diary and actigraphy, plus 48-h recordings of core body temperature. The circadian rhythm of temperature was described by partial Fourier time-series analysis (with 12- and 24-h harmonics). The temperature peak and trough values and clock times did not differ between groups. However, the temperature rhythm was biphasic in monks and nuns, with an early decrease at 19:39 ± 4:30 h (median ± 95% interval), plateau or rise of temperature at 22:35 ± 00:23 h (while asleep) lasting 296 ± 39 min, followed by a second decrease after the Matins Office, and a classical morning rise. Although they required alarm clocks to wake-up for Matins at midnight, the body temperature rise anticipated the nocturnal awakening by 85 ± 15 min. Compared to the controls, the monks and nuns had an earlier sleep onset (20:05 ± 00:59 h vs. 00:00 ± 00:54 h, median ± 95% confidence interval, p = .0001) and offset (06:27 ± 0:22 h, vs. 07:37 ± 0:33 h, p = .0001), as well as a shorter sleep time (6.5 ± 0.6 vs. 7.6 ± 0.7 h, p = .05). They reported difficulties with sleep latency, sleep duration, and daytime function, and more frequent hypnagogic hallucinations. In contrast to their daytime silence, they experienced conversations (and occasionally prayers) in dreams. The biphasic temperature profile in monks and nuns suggests the human clock adapts to and even anticipates nocturnal awakenings. It resembles the biphasic sleep and rhythm of healthy volunteers transferred to a short (10-h) photoperiod and provides a living glance into the sleep pattern of medieval time. (Author correspondence:

About Tore Nielsen

Researcher at University of Montreal and Director of Dream & Nightmare Laboratory
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