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Brain Scans Help Decode Sleepers' Dreams

Scientists from Japan reported at a conference last week how brain scans helped them decode the visual content of volunteers' dreams as they slept. They suggest their findings support the idea that dreaming and perception share the same brain circuits.

Study leader Yukiyasu Kamitani of the ATR Computational Neuroscience Laboratories in Kyoto, and colleagues, used functional magnetic resonance imaging (fMRI) to scan the brains of three male volunteers as they slept, while also recording electroencephalograms (EEG) of their brain waves.

They presented their findings at Neuroscience 2012 in New Orleans on Sunday 14 October. Dreaming Research Dreaming is a subjective experience that is often accompanied by visual content. However, little if anything is known about the brain circuits involved.

Previous studies have tried to link physiological states with dreaming, but have not been able to show links between specific visual contents of dreams and patterns of brain activity.

(Nevertheless, there have been some remarkable discoveries, such as that of the German scientists who reported in the July 2012 online issue of SLEEP, how they compared brain scans taken during "lucid dream" episodes, to brain scans taken during normal dream states, and found which centers of the brain become active when we are aware of ourselves, the so-called state of "metaconsciousness".) Neural Decoding Kamitani and colleagues decided to see if they could use a new technique called neural decoding, which infers specific contents of visual experience from patterns of brain activity. For example, the method shows how particular brain activity patterns are tied to the recognition of specific objects.

They wondered if it might be possible to use it to look at brain activity during sleep, and thereby decode the visual content of dreams.

Thus using fMRI and EEG, they took brain scans and recorded brain waves of the three men as they slept.

They woke the men up when their EEGs showed a particular pattern, and asked them to freely describe their visual experiences just before awakening, and then asked them to go back to sleep. On some occasions it meant waking them up ten times per hour.

Each volunteer reported having visual dreams just before waking six or seven times per hour. The researchers repeated the procedure until they collected over 200 dream reports over a total of 30 to 45 hours of experiment time for each volunteer. The experiment took several days for each participant.

Most of the volunteers described dreaming about everyday things, but some dreams were more unusual, for example one described being in conversation with a famous actor.

The researchers looked for key words that appeared frequently in the content of the volunteers' dream reports and arrived at 20 categories, including words like "female", "male", "car", and "computer".

Then, using photographs to represent each category, they scanned the volunteers' brains again as they looked at the images, and compared them with those taken just before the participants were woken up during the dream experiments.

They analyzed activity in several brain areas, including V1, V2 and V3, which play a role in the early stage of visual processing, such as encoding basic characteristics like contrast and orientation. They also analyzed activity in areas involved in higher order visual processing (around LOC, FFA, and PPA), which are important for object recognition. Predicting Dream Content When they analyzed their results, the researchers found the decoding performance was "significantly higher than chance level in the higher visual areas".

"We built a model to predict whether each category of content was present in the dreams," says Kamitani, in a report on the study by Nature News.

"By analysing the brain activity during the nine seconds before we woke the subjects, we could predict whether a man is in the dream or not, for instance, with an accuracy of 75 - 80%," he adds.

He and his colleagues conclude their study shows that:

"... fMRI signals in the visual cortex, especially in the higher visual areas, represent specific visual contents of dreams, allowing for the prediction of dream contents. Furthermore, it supports the hypothesis that dreaming and perception may share neural representations in the higher visual areas."

The team now plans to do the same kind of experiment with rapid eye movement (REM) sleep, which also involves dreaming. They suggest knowing more about the content of dreaming will help us work out what it is for.

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