Re-experiencing old dreams while being wide awake might seem like some kind of fiction, but a new study revealed that it's possible. Researchers at Toulouse University Hospital in France found that stimulating the temporal lobe – part of the brain that's responsible for long-term memory and dreaming – can allow the person to relive the experiences they've had in the sleep.
The phenomenon known as déjà-rêvé meaning 'already dreamed' is seen in people suffering from epilepsy. There are reports of them remembering old dreams during seizures or electrical brain stimulation (EBS).
However, there was no neuroscientific evidence to support the existence of déjà-rêvé and was commonly mixed up with déjà-vu. With the new study, the researchers explained: "This study demonstrates that déjà-rêvé is a heterogeneous entity that is different from déjà-vu, the historical "dreamy state" definition and other experiential phenomena."
They added: "This may be relevant for clinical practice as it points to temporal lobe dysfunction and could be valuable for studying the neural substrates of dreams."
Researchers collected the data of dream recalling sequences of the epileptic patients (2003–2015). The content of the déjà-rêvé and the location of EBS were analyzed, scientists mentioned in their research paper.
In the study, the researchers analyzed déjà-rêvé induced by EBS in epileptic patients undergoing pre-neurosurgical assessment. They reviewed all the reported déjà-rêvé induced by EBS to clarify its definition, its phenomenology, and its content.
"EBS-induced déjà rêvé could be an interesting approach to better understanding physiological dreams that cannot be reproduced under laboratory conditions," said the study authors.
"Most studies focus on REM (rapid-eye movements) sleep period and dream reports obtained by awakening a sleeping subject. However, non-REM sleep dreams account for a significant portion of all typical dreams and several factors might render dream reports less trustworthy — especially the sleep stage before awakening — when compared with reports of waking experience," they added.
Three Kinds of Déjà Rêvé
The study states that there are three kinds of déjà rêvé. One of it is referred as "episodic-like" -- where a patient can spontaneously specify that they had a certain dream on a certain date.
"'I saw something, a dream, a nightmare I had a couple years ago. A dream of an object lying on a table," said one of the study participants.
Another one is referred as "familiarity-like" – where a patient recollects a vague dream or elements of the dream. One subject explained that they had a vision of a scene from a recent dream.
The last type is "dreamy-state" -- where the subject will have a feeling of being in a dream or nightmare. A subject tried to explain it as feeling like they passed out and floating.
Déjà rêvé is still a new phenomenon, but the recent study is the first step to explain the dreamy feelings people have.
The findings were published in the journal Brain Stimulation.