When I was 13, I punched a wall. It wasn’t an act of teenage rebellion; I was lost in a dream. As someone who experiences lucid dreams, my nighttime escapades are usually vivid and often under my control. However, this particular dream took a turn. I found myself boxing a faceless opponent in a fight for my life, and in a moment of lost control, I struck the wall. The pain in my fist jolted me awake.
There are times when my dreams are so intensely detailed that I wake up feeling drained, leading me to question whether I’d be better off without them.
Thanks to recent advancements in neuroscience, that possibility might not be too far off.
Experts are currently witnessing a renaissance in our understanding of REM — rapid eye movement — sleep. This stage of sleep is linked to our most vivid dreams and is thought to play a crucial role in learning and even influence migraines. The regulation of REM sleep is significant in sleep disorders like narcolepsy, where the lines between wakefulness and dreaming blur. In the past couple of years, researchers have made significant progress in deciphering the neural pathways that control REM sleep.
For example, just three weeks ago, a study published in the journal Nature showcased how scientists developed a light switch to turn REM sleep on and off in mice. Led by UC Berkeley neuroscientist Yang Dan, the researchers employed optogenetics, a method that allows individual neurons to be activated using laser light from a fiber optic implant. In this study, the mice were genetically modified to possess light-sensitive neurons in their brain stem.
REM sleep was first identified in the early 1950s, and during that decade, groundbreaking research by Michel Jouvet revealed the significance of the brain stem in REM sleep. Jouvet’s studies demonstrated that lesions in the brain could disrupt the neural pathways responsible for one of the hallmark features of REM sleep: muscle paralysis, also known as muscle atonia.
REM sleep is the final stage in a cycle of five stages that we experience while sleeping. As individuals progress through the initial four stages of non-REM sleep, their slumber deepens. Muscle movements become less frequent, and brain waves slow down, interspersed with occasional bursts of rapid waves called sleep spindles. We remain in deep, non-REM sleep until our minds suddenly shift into REM sleep. At this point, brain waves change again, becoming fast and irregular. Our eyes move rapidly, and our muscles become entirely paralyzed.
Muscle atonia prevents us from acting out our dreams, and it was previously thought that the brain stem neurons responsible for this paralysis were distinct from those that induce other aspects of REM sleep. However, Dan and her team discovered a cluster of neurons in the ventral medulla—a section of the brain stem—that can perform both functions.
When these neurons were activated using laser light, they induced REM sleep rapidly within 30 seconds, as observed through electroencephalogram (EEG) and electromyogram (EMG) scans.
“What’s surprising about their study is that when they activated and inactivated the area, they didn’t get what you expect: muscle paralysis or movement during REM,” noted John Peever, a neuroscientist at the University of Toronto who was not part of the research. “Instead, they found that stimulation could actually alter the length and frequency of REM sleep.”
The researchers conducted this experiment on nearly 100 different mice and discovered that toggling these neurons prompted the transition from non-REM sleep to REM sleep 93 percent of the time. The duration of REM sleep was also affected.
The light switch, however, cannot make a mouse transition directly from being awake to REM sleep, which is a hallmark of narcolepsy—a condition where both animals and humans unexpectedly fall into deep sleep. According to Dan, these brain cells appear to act as a switch for REM when mice are already in a sleep state.
When REM walls crumble
Alright, the findings with the mice are fascinating, but what implications do they have for humans? If my most vivid dreams happen during REM sleep, could this knowledge be used to turn them off?
Peever mentioned that the REM neurocircuits in the brain stem likely don’t influence the content of dreams, but these nerves do seem to play a role in either promoting or limiting REM sleep. Additionally, he noted that clinical data from postmortem brains indicates that the area affected by Dan’s team shows degeneration in individuals with REM sleep behavior disorder. Those with this disorder experience a loss of muscle paralysis during REM and often act out their dreams with complex movements.
