Involuntary eye movements made during sleep may reflect the changing visual scenery of our dreams, according to new research.
Since the 1960s, researchers have been trying to join the dots between the involuntary eye movements made during sleep, spikes in brain activity and the imagery of our dreamscapes, with little success.
But a study from an international team of scientists suggests that the eye movements are linked to the moment that the images of a dream switch. The findings offer new insight into what’s going on deep inside the visual brain during sleep.
As we nod off our brain starts to cycle through a number of stages of sleep. In the 1950s two scientists discovered that the eyes periodically darted about frantically. They called this stage rapid eye movement (REM) and it has since been found to be the most active phase of sleep, with brain waves spiking and in which we are believed to experience vivid dreams.
In the latest study, led by Dr Yuval Nir from the University of Tel Aviv, researchers explored the relationship between the eye movements of sleep and activity in the brain’s visual system.
They monitored the brain activity of 19 patients with epilepsy at the University of California, Los Angeles (UCLA) medical centre in the US. Electrodes inserted into the brains of the test subjects provided researchers with a rare glimpse into what individual brain cells, or neurons, are doing during sleep. The patients’ electroencephalography (EEG), eye movements and muscle tone were also recorded.
The results showed that Rapid eye movements during sleep correlated with spikes in the activity of brain cells in the medial temporal lobe, the part of the brain associated with vision and memories. This brain activity is similar to that exhibited by someone after they view images of famous people or places.
Dr Nir said: “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.”
Senior author, Dr Itzhak Fried, Professor of Neurosurgery and Psychiatry & Biobehavioral Sciences at UCLA, said: “The research findings suggest that rapid eye movements represent the moment the brain encounters a new image in a dream, similar to the brain activity exhibited when one encounters visual images while awake.”
Dr Nir added: “How and why eye movements occur are important, and these moments represent privileged windows of opportunity for the study of brain activity.”The research was published in the journal Nature Communications.