Why we dream has long baffled scientists, with multiple theories emerging over their purpose. However, they might have worked out where dreams come from in the brain after discovering REM (rapid eye movement) sleep is very similar to the brain activity seen during waking vision.
Their findings, published in the journal Nature Communication, suggest REM in sleep could be the changing scenery of a dream and explains why people waking from this phase of sleep often report vivid dreams. "Current results may imply that REMs during sleep reflect a change of the visual imagery in dreams, but future studies are needed to unequivocally establish this possibility," the scientists wrote.
Researchers recorded the brain activity of 19 epilepsy patients, examining the medial temporal lobe and neocortex during sleep and wakefulness and during visual stimulation. Their findings showed that during wakefulness and REM sleep, there was distinctive brain activity. Individual neurons were seen to have reduced activity prior to REMs, while increases were recorded immediately after – a similar patter to that seen when participants were presented with an image while awake.
The international team of scientists came from Tel Aviv University, France's Laboratoire de Sciences Cognitives et Psycholinguistique and Brain-Cognition-Behaviour Doctoral School, the University of Wisconsin Madison and UCLA.
Corresponding author Yuval Nir told IBTimes UK that they used epilepsy patients because they provided the opportunity to record high-quality data of electrical activity from inside the human brain – the patients had agreed to take part in the study while taking part in different treatments that required this sort of monitoring.
He also said they believe the results could be generalised to the population as they discarded any measurements that were diagnosed as a seizure onset zone and only included those from healthy tissue. They avoided measurements taken when patients suffered from a seizure. "We tried to be very careful," Nir said. "These results are tapping on a unique opportunity where these epilepsy patients are treated and brain activity monitored for clinical reasons, so we do the best we can with those data."
The team was also not able to gather dream reports, which would have provided a greater insight into the nature of the dreams during REM. The participants involved were on hospital wards and many had been for brain surgery.
Nir said: "They're sometimes in pain and very uncomfortable and they're very brave to volunteer with our research. On top of all that to wake them up five times per night to ask what they were dreaming about – we have to be sensitive and remember we're working with people in a delicate situation."
However, he said if they could get this information in future research, it could be the "holy grail" of dream study. Nir said: "I wish we had such data. Previous research has established that individual neurons in the brain can respond to very specific pictures, like Jennifer Aniston or the Eiffel Tower.
"In principal, we could track activity of that specific neuron to see what dreaming and moving the eyes at that specific moment that neuron is active and then wake up the person to see what they were dreaming about... Conceptually speaking, that should be possible and that would be the holy grail of such research. That would be something to try to do in the future with patients that express a specific interest in the study and were happy to out."
Nir said they are also looking to understand the relationship between the brain activity during different states of consciousness, for example wakefulness, sleeping and under anaesthesia.
What are dreams?
While the findings do not explain what dreams are or why we have them, Nir said there are several important implications that can be inferred from the study. He said the time points when the eye moves are significant and you can see a recess in brain activity – which could be used to identify memory formation and therefore boost memories. "It gives us an important clue that even spontaneously, those moments are like privileged time windows where there's a natural reset and maybe we can tap into that reset," Nir said.
An example of this could be someone suffering from post-traumatic stress disorder (PTSD) – by identifying these memories, scientists could one day zoom on these time points to perform focused manipulation of brain activity during dream sleep.
In addition, they can now measure the frequency of the activity of these neurons. Nir added: "For example they don't burst after each and every eye movement, they do so after a percentage. So if we were to find in a certain individual that neurons pattern we see is very similar, like the same snapshot repeating, that would be sort of the mental experience of repeated images in a dream."