Geneva, London – A team of scientists from different countries have unpicked the regions of the brain involved in dreaming and acting as the “Hallmark of Dreaming.”

Dreams had long been known to occur during different phases of sleeping, but researchers didn’t know the exact reason behind them. Dreams occur largely during rapid eye-movement (REM) sleep, a period of slumber involving fast brain activity, however, they have also been reported to occur in REM sleep characterized with low brain activity.

In previous studies, participants being woken during the REM sleep didn’t see dreams.

To collect more data on dreams and their characteristics during both phases, researcher Francesca Siclari and colleagues from the US, Switzerland and Italy, carried out a series of experiments involving 46 participants, each of whom had their brain activity recorded while they slept by electroencephalogram (EEG) – a noninvasive technique that involved placing up to 256 electrodes on the scalp and face to monitor the number and size of brainwaves of different speeds.

All involved participants were being woken at various points throughout the night and asked to report whether they had been dreaming. Analysis of the EEG recording revealed that dreaming was linked to a drop in low-frequency activity in a region at the back of the brain dubbed by the researchers the “posterior cortical hot zone.”

Researchers observed the brain’s activity and correctly predicted instances of dreaming and no dreaming 90% of the time.

In another experiment involving seven participants who were trained to describe their dreams in details, the researchers analyzed the brain activity during REM and found that dreaming about faces was linked to increased high-frequency activity in the region of the brain involved in face recognition, with dreams involving language or speech perception similarly linked to regions of the brain that handle such tasks when awake.