For most people the following experience will sound familiar: Just before you fall asleep, you suddenly feel like you’re falling into a deep ravine followed by a violent shock that instantly jolts you back to conscienceness. What causes this strange convulsion and why does it occurs only occasionally?
“Falling asleep is not a matter of turning a button on or off,” explains neuroscientist Ysbrand van der Werf, who works at the Sleep and Cognition Group of the Dutch Institute for Neuroscience (VUmc). “The different parts of the brain don’t fall asleep simultaneously, but one after the other, and this process varies every day depending on the circumstances and what you’ve done that day. For example, if you’re exhausted, all parts of the brain fall asleep at the same time. But if you’re lying in an uncomfortable position, or are stressed, then the transition may take longer.”
In those few minutes between sleeping and awake, the brain areas that control muscles can already be asleep, while the brain areas that process sensory information (perception) are still awake. Van der Werf: “When you fall asleep, your muscles relax and this relaxation is registered in another part of the brain that might still be awake. In a reflex you then tighten all your muscles.”
The most fascinating part is perhaps that one second just before you wake up, in which you feel like you’re falling into the deep. According to van der Werf, it remains unclear if people are actually experiencing this, or that they think they have experienced this due to a reconstruction created by their brain after the sudden wake up.
Three quarters of people occasionally suffer from these so called hypnagogic shocks, but it’s no reason for concern, according to Van der Werf. “It is a benign phenomenon that does not disturb sleep.”
Source: De Volkskrant
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Another research of Ysbrand van der Werf, published in Nature: Van Der Werf, Y., Altena, E., Schoonheim, M., Sanz-Arigita, E., Vis, J., De Rijke, W., & Van Someren, E. (2009). Sleep benefits subsequent hippocampal functioning Nature Neuroscience, 12 (2), 122-123 DOI: 10.1038/nn.2253