A new study on men in Germany indicates that hypnotic suggestions presented before a 90-minute afternoon nap and aimed at promoting slow-wave sleep led to the increase in the release of prolactin and aldosterone. It also reduced the predominance of the sympathetic side of the autonomic nervous system. The study was published in Communications Biology.
Sleep is a fundamental biological process that plays a crucial role in a number of health aspects by modulating immune functions, growth, cardiovascular activity, metabolism, and other functions. It supports brain functions such as attention, memory, emotional regulation, and problem solving. It also regulates the activity of the autonomic nervous system, thus having a wide-reaching effect on the whole body.
Sleep occurs in several stages, the deepest of which is slow-wave sleep. Slow-wave sleep is thought to play a major role in regulating the release of various hormones including the growth hormone, cortisol, prolactin and aldosterone. It also regulates the autonomic nervous system by reducing the activity of the sympathetic side of this system, the part of the system that is the most active when the organism is under stress or physically active.
Hypnosis, “a state of consciousness involving focused attention and reduced peripheral awareness” has been used in the past to treat sleep disorders and regulate sleep quality. In this study, Luciana Besedovsky and her colleagues wanted to explore whether hypnosis use to enhance slow-wave sleep can also invoke changes to endocrine and autonomic nervous system parameters.
“Twenty-three healthy young, medium- to high-hypnotizable men participated in two experimental sessions, each encompassing a 90-min afternoon nap in the sleep lab. In one session, participants listened to an audio tape that included hypnotic suggestions to sleep deeper (Hypnosis condition) while falling asleep, whereas in the other session, they listened to a neutral control text (Control condition). Sleep was recorded polysomnographically, including electrocardiography for determination of heart-rate variability (HRV),” the researchers explained.
The researchers took participants’ blood samples 90 minutes before the sleep session, every 5 minutes after that for 90 minutes, and 10 and 20 minutes after the sleep session was over. Participants were selected for participation by their suggestibility to hypnosis (required to score at least 7 on the Harvard Group Scale of Hypnotic Susceptibility).
Results showed that hypnotic suggestion increased the absolute time spent in slow-wave sleep by almost one half compared to controls. Total sleep time, duration of sleep (wake after sleep onset), time to fall asleep (sleep onset latency), and subjective quality of sleep remained unchanged.
Growth hormone levels were also strongly increased in the hypnotic suggestion group, compared to control. “The increase started at around 40 min after turning lights off, reaching a maximal difference relative to control of more than 400% after 75 min. Furthermore, increases in growth hormone levels from the Hypnosis to the Control condition were correlated with increases in the time spent in slow-wave sleep. Prolactin and aldosterone levels were also increased, albeit to a lesser extent,” the researchers wrote.
Lymphocyte counts were not affected by the experimental treatment, but examination of autonomic system activity showed a shift towards reduced predominance of the sympathetic part of the autonomic nervous system.
“This simple to use hypnotic technique does not only promote central nervous slow-wave sleep, but also impacts the major downstream mediators of the peripheral effects of sleep, demonstrating the physiological significance and validity of this method of slow-wave sleep enhancement,” the researchers explained. “Since the affected parameters serve various essential physiological functions, including regulation of growth, metabolism, immunity, tissue repair, and cardiovascular activity, the present findings open up a wide range of potential applications of the employed hypnotic suggestions.”
The study sheds light on the relationship between psychological states and important physiological factors. However, it should be noted that the study sample was small and all participants were healthy young men selected for their suggestibility to hypnosis. Women are known to have different sleep architecture with more slow-wave sleep, so study results on them might have been different. Results might also differ on people of other ages, cultures and less susceptibility to hypnosis.
The hypnotic suggestion audio clip used in the study can be downloaded in the .mp3 format from the University of Freiburg website.
The study, “Hypnotic enhancement of slow-wave sleep increases sleep-associated hormone secretion and reduces sympathetic predominance in healthy humans”, was authored by Luciana Besedovsky, Maren Cordi, Laura Wißlicen, Estefanía Martínez-Albert, Jan Born, and Björn Rasch.
