Why Do We Remain Still While We Sleep?

Why does our body remain inactive during sleep? We often experience vivid dreams which the brain encounters as real experiences. Yet, we remain still while we are busy fighting James Bond in our heads.

Scientists are closing in on the mechanism that prevents our muscles from being active during REM sleep, termed ‘sleep paralysis’. If you have ever twitched or kicked in your sleep, you have experienced an instance of a temporary loss of sleep paralysis (though this is usually experienced in periods of light sleep). Researchers at the University of Toronto have now discovered two chemicals that ‘switch off’ regions of the brain that activate muscle cells during deep sleep.

Some Brain Biology

Our muscles are ‘paralysed’ during sleep to protect the body from potential injury.

How does the brain transmit signals? Chains of brain cells, called neurons, are arrayed from head to tail from the origin of the brain signal to the destination. Each neuron releases chemicals called neurotransmitters which then activate the next neuron. This neuron in turn activates the next neuron, and so on till the signal reaches the target region (for example, motor regions that activate muscles).

In this experiment, receptors for two neurotransmitters—GABA and glycine— were blocked in trigeminal neurons of mice. These are the neurons which activate facial muscles. On blocking these receptors, the mice were found to exhibit muscle activity even during deep sleep, meaning that these two chemicals are essential in maintaining the passivity of muscles during sleep. Moreover, both these chemicals had to be blocked simultaneously for the muscles to start moving. This also means that these two chemicals work independently of each other.

Potential for Treating ‘Sleep Paralysis’ Disorders

This result could play an important role in the research on REM sleep disorders in which patients act out their dreams. We potentially have molecular targets that could be aimed at to treat these disorders. Moreover, “understanding the precise mechanism behind these chemicals’ role in REM sleep disorder is particularly important because about 80 percent of people who have it eventually develop a neurodegenerative disease, such as Parkinson’s disease,” study author Peever said.

Published by

Shweta Ramdas

Beginning life as a grad student studying human genetics.