Rapid Eye Movements which occurs during sleep is an indication that the person is dreaming and brain is capturing visual images with darting eyes.
When a person is in the REMs (Rapid Eye Movement sleep) phase, the eyes move rapidly and randomly. For decades, scientists hypothesized that during this phase of sleep a person would experience an animated dream sequence which is similar to how a person views the world while they are awake.
Although scientists had hypothesized about REMs for a long time, they did not have proper evidence to prove this phase.
In a new study, conducted by researchers at Tel Aviv University in Israel, scientists from France and Israel came together to investigate the actual details of REMs. Scientists were able to demonstrate that each movement of the eye reflects a new visual information in our dreams which means that the brain captures visual images when the eyes are moving during sleep and the person is actually able to see a new image in the dream world.
According to New Scientist, co-author Yuval Nir, of the Sackler School of Medicine at Tel Aviv University, said: “People who were woken up when their eyes were moving from left to right would say they were dreaming about tennis, for example.”
For instance, scientists believed that in case of people who act out of their dreams, the eye movements were in sync with their actions.
Some five years back, in 2010, scientists had investigated people who had REM sleep behavior disorder. In this disorder, most of the times people physically act out of their dreams and hence their eye movements match with their action almost 80 percent of the times. The study has been published in the journal Brain. The disorder was explained with an example, wherein during the study it was observed that a man who smoked in his dream would physically appear to hold a cigarette and even put it out in an ashtray. His eye and head movements also indicated that he was focusing on the cigarette which he was putting out in an ashtray as per his dreams.
During REM sleep, it was observed that a person experiences low paralysis throughout the body and there is hardly any movements in the body. On the contrary, the neuron activity of the brain becomes very much intense and it is pretty similar to that when a person is fully awake. This according to scientists is the reason for the electrical brain activity.
Over a span of four years, Nir and his colleagues carried out invasive methods on 19 epileptic patients at the UCLA Medical Center and were able to record the actual activity of the brain from within the brain.
Normally scientists stick to non-invasive methods and study the brain from scalp to see through the brain’s behavior during sleep and check if it was linked to more of physical movement or processing of the visual images.
However, in this recent study, scientists used invasive methods and inserted electrodes deep inside various regions of the brains of the epileptic volunteers, most importantly the medial temporal lobe, as this is the region which is responsible for producing reaction to images.
According to researchers, the invasive procedure was inevitable as all the 19 patients were being prepared for surgery which involved the surgical cut down of the seizure-causing areas of their brains.
The brain activity was monitored for a period of 10 days and then the recordings from the electrodes were used for study and interpretation.
In a press release Nir said: “We focused on the electrical activities of individual neurons in the medial temporal lobe, a set of brain regions that serve as a bridge between visual recognition and memories. [P]rior research had shown that neurons in these regions become active shortly after we view pictures of famous people and places, such as Jennifer Aniston or the Eiffel Tower — even when we close our eyes and imagine these concepts.”
The research study comprised of three different settings:
- REM sleep brain activity
- Wakeful eye movements in darkness
- Wakeful fixed-gaze visual processing
The brain activity of these epileptic patients was then compared across the three settings. The volunteers were made to sleep and the brain activity of around 40 neurons in each of the volunteer was recorded by the research team. With the help of EEG (electroencephalogram) electrodes that were placed on the scalp of each volunteer, the research team measured the signals emitted from the brain. Simultaneously they even tracked the eye and muscle movements of each volunteer. When the patients came out of their sleep and were fully awake, they were shown an image which was associated with a memory.
Researchers observed that during the REMs phase, the brain cells in the medial temporal lobe would always reflect same activity irrespective of the different settings which the patient was during the study. Meaning regardless of whether the patient is awake or asleep or fixated their gaze on the images that were presented to them during the study, the neurons which were present in the hippocampus have shown to be bombarded with activity during the REMs phase of sleep and the activity was seen more often in a scenario when the brain cells were processing new visual images.
Thus Nir concluded: “The electrical brain activity during rapid eye movements in sleep were highly similar to those occurring when people were presented with new images. Many neurons — including those in the hippocampus — showed a sudden burst of activity shortly after eye movements in sleep, typically observed when these cells are ‘busy’ processing new images.”
During a news release, Dr. Itzhak Fried, senior author of the study and a professor of neurosurgery at the David Geffen School of Medicine at UCL, said: “This electrical pattern closely resembles what happens when we view something new in waking life. We suspect rapid eye movements reflect the instant when the brain encounters a new image in a dream.”
Researchers thus concluded that rapid eye movements when a person is asleep indicated the moment when that person is actually encountering some new image in their dream. Researchers further suggest that this moment is pretty similar to the situation when a person would see a new photo while they are awake.
The only difference here is that, during the study researchers did not wake up their patients hence it is not clear as to what exactly they were dreaming; however the study revealed that the brain keeps switching between different mental images during the REMs phase.
The details of study and findings have been published in Nature Communications.