Scientists have identified a specific pattern of activity at the back of the brain which could then predict whether a person was having a dream. Their findings confirm that dreaming can occur both during rapid-eye movement (REM) sleep and non-REM (NREM) sleep.
Researchers have traditionally associated dreaming with the high-frequency brain activity they observed during REM sleep, and which appeared similar to the kind of brain activity seen when people were awake. In contrast, low-frequency brain activity during NREM sleep was interpreted as an absence of dreams.
However, many studies have shown that when people are awakened during NREM sleep, they are able to report dream experiences, while a minority of subjects deny having any dreams during REM sleep.
"The influential notion that dreaming is synonymous with REM sleep has dominated for the past several decades, despite the increasing number of studies suggesting that dream reports can be obtained from every stage of sleep, albeit less often", study co-author Lampros Perogamvros told IBTimes UK.
"Indeed, previous studies showed that up to 70% of NREM sleep awakenings yield reports of dream experiences".
These different cases challenged scientists' understanding of the neural correlates of dreams.
In a study now published in the journal Nature Neuroscience, scientists have used a technique known as high-density electroencephalography which records electric activity to investigate the link between brain activity and dreams.
They compared what happens to the brain when people report dreaming during REM and non-REM sleep.
Waking up the dreamers
The scientists recruited 32 participants and recorded their brain activity while they slept. They woke them up at various points during the night and asked them whether they had dreamt – and if so, what the dream was about.
They were quickly able to pick out a pattern of brain activity associated with dreaming in a region at the back of the brain (which the authors called ''the posterior cortical hot zone'').
This pattern – decreased strength of low-frequency brain activity and increased strength of high-frequency activity - could be seen when people reported dreaming, both during REM and NREM sleep. Whether the participants were able to recall the content of the dream didn't change anything.
Spotting this combination of decreased low-frequency and increased high-frequency activity strength at the back of the brain subsequently helped scientists predict, in real time, when people were dreaming during NREM sleep, with about 90% accuracy.
In future studies, the authors would like to answer even more questions, such as whether dreaming has a specific function.