New research uncovers a brain-body network that creates our dreams
So much of the research into how and why we dream has focused on the brain rather than the body… with the possible exception of nightmares where physiological fear responses are clearly a part of the experience. My sense of dreaming has always been that it is deeply embodied, and dynamically responsive to both our thoughts and emotions in an intricate dance. This may indeed be the case as a team of Italian researchers propose activation of the brain-heart axis is a trigger for dreaming.
New research led by Mimmi Nardelli has uncovered what I have always suspected was there: a body-mind link that drives dreaming, a bi-directional link where the body affects our dreams, and our dreams affect our bodies. The research team at the University of Pisa performed a comprehensive analysis of physiological signals during dream-rich REM sleep with nine healthy dreamers tracking brain and nervous system dynamics associated with dream recall. They also looked at causal directions not just correlations. They concluded that “bodily changes play a crucial and causative role in conscious dream experience during REM sleep.”
Much of the physiological dream research conducted to date has focused on neural correlates of dreaming, but this study also examines its relationship with the central and autonomic nervous system using measures of heart rate variability and blood pressure, along with EEG (brain) signals. Heart rate variability is a reliable measure of the state of the autonomic nervous system, which governs the body’s responses to cues of threat and safety. Blood pressure can also indicate levels of sympathetic activation.
The authors of the study noted that previous studies of nervous system correlates focused on discriminating sleep stages – for example, several studies investigating heart rate variability dynamics found a shift from vagal to sympathetic activity during REM. According to the Polyvagal Theory developed by Stephen Porges, this would indicate a shift from a sense of safety to one in which the body mounts a response to threat. This study goes beyond study of sleep stages to uncover new information about the relationship between dreams and the body.
During the experiment, researchers woke participants up during REM sleep and asked about their dreams – did they recall one, and was it positive or negative? They captured physiological data from the minutes prior to awakening and compared instances of dream recall with those where no dream was recalled.
Dreams and emotions linked
Previous studies have shown that in dreaming, the right hemisphere of the brain, more associated with visuo-spatial functiong and non-conscious emotional perception, is more active during dreaming, while activity in the left frontal hemisphere, associated more with logic and executive functioning, decreases. These finding were supported in this study. With respect to heart rate variability, when a dream was recalled, an overall increase in sympathetic activity, and parallel decrease in vagal activity, was observed. The authors speculate that these findings indicate emotional arousal during dreaming.
In their study of changes in the nervous system over time in relation to dreaming, the authors found evidence to support a long-standing ‘activation-synthesis’ theory by Hobson and McCarley (1977) that dreaming arises from sensorimotor information relayed from the brain stem to the cerebral cortex. The current study suggest this is only half true. They found a bi-directional influence – a dynamic interchange from body to brain and brain to body.
The researchers wrote: “Results from the heart-to-brain interaction analysis suggest that the interactions between CNS and ANS associated with dreaming experience are bidirectional and exhibit dynamic changes.” They are quick to point out the results are preliminary because the sample size was small and low in statistical power. However, the study points to something I have come to believe about dreams: that their images are a picture of our embodied emotional state that impacts us deeply – and that we can also impact our dreams and how they unfold. They respond to us and we to them.
References
Hobson, J. A. & McCarley, R. W. (1977). The brain as a dream state generator: an activation-synthesis hypothesis of the dream process, The American journal of psychiatry.
Nardelli, M., Catrambone, V., Grandi, G., Banfi, T. (2021). Activation of brain-heart axis during REM sleep: a trigger for dreaming. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. https://doi.org/abs/10.1152/ajpregu.00306.2020