Eye movement during sleep is evidence that we are really staring at the pictures our brains have conjured up in our dreams. Because the brain processes them with the same neurons that handle wakefulness, these visuals fool us into thinking they’re genuine. Until data from our senses shakes us out of it.
According to a recent study out of the University of California, San Francisco, when our eyes move during rapid eye movement (REM) sleep, we’re really gazing at objects in the dream world that our brains have built.
The researchers add that this discovery opens a window into the cognitive processes of the sleeping brain, illuminating not just the nature of dreaming but also the function of the imagination during sleep.
Since the 1950s, the stage of sleep characterized by rapid eye movement (REM) has been recognized as the time during which dreaming takes place. However, experts are still debating what the eyes are for.
Based on the findings of the latest studies, it is now clear that our eye movements during sleep are not random but rather connected with events in the dream world. The study’s primary author, Massimo Scanziani, and his colleagues found that the same brain regions used to interpret real-world information and dream imagery did so throughout sleep and awake in mice.
Scanziani believes this discovery “gives us insight into the cognitive processes that occur when the brain is sleeping” and answers a question that has intrigued scientists for decades.
Some specialists in the second part of the twentieth century speculated that these rapid eye movement (REM) movements could occur in response to scenes in the dream world, but there has been no method to establish this.
Results from the possible studies (seeing where dreamers’ eyes went and then asking them when they woke up where they were gazing in the dream) were contradictory. As a result, many scientists have assumed that REM movements just happen randomly, with no particular purpose other than to keep the eyelids moist while sleeping.
Scanziani and Yuta Senzai, with somewhat more sophisticated technologies, have resolved this uncertainty about eye movements. They were able to determine this by studying the activity of “head direction” cells in the mouse brain during rapid eye movement (REM) sleep.
Neurons called head direction cells (HD cells) are spread throughout the brain and are responsible for processing sensory data; their firing rates rise only when an animal’s head is oriented in a certain direction. It is believed that all mammals have this kind of neuron, which has been identified in rodents, primates, mice, chinchillas, and bats.
These HD neurons function like compasses, guiding the animal around its surroundings based not on the Earth’s magnetic field but on landmarks and the animal’s own movements.
HD cells are thought to form the neuronal substrate for the direction the organism perceives it is going in its surroundings, making them crucial for accurate navigation.
The study’s authors examined the mouse thalamic head-address system (HD), a neuronal population whose activity guides both the awake mice’s “actual” perception as they investigate their surroundings and the dreamy “virtual” vision of sleeping mice.
The group monitored the mouse’s eye movements in real time and compared them to the data captured from these HD cells concerning the mouse’s head orientations. This allowed him to find that, much as when the mouse is up and moving, the direction of the eye movements corresponded with what the mouse’s internal compass suggested during REM sleep.
According to the findings, the mouse’s eye movements are synchronized with the events unfolding in its dream simulation. This suggests that our dream pictures are analyzed by the same neurons that are active while we are awake and processing real-world events.
Scanziani provides a crucial nuance: although our awake brain uses the same neurons to analyze dream imagery, our unconscious mind allows us to mix things that are physically impossible during sleep (for example, when we dream that we fly).
Just how is it even possible? Since there are no external stimuli to wake us up from dreaming, sleep may lead to disorientation. Scanziani argues that this is why the dream is an idealized, unified, and deceptive reality.
How these different parts of the brain coordinate to create the seemingly natural ability to generate the impossible is something that Scanziani wishes to investigate more. “It’s crucial to know how the mind is continually revised in light of new information,” he argues.
How our experiences shape our unique mental representations of the world may be better understood by learning more about the processes that enable us to coordinate so many diverse sections of the brain during sleep, as Scanziani puts it.
