Decoded: Why you remember dreams

London, Feb 17 (IANS) Don't know why you can't remember the dreams while your wife can recall most of those?

The reason for dreaming is still a mystery, but scientists have now found out the differences between the 'high-dream recallers' - who recall dreams regularly - and 'low-dream recallers' who recall dreams rarely.

The secret lies at the temporo-parietal junction of the brain - an information-processing hub - which is more active in high dream recallers.

"Increased activity in this brain region might facilitate attention orienting toward external stimuli and promote intra-sleep wakefulness, thereby facilitating the encoding of dreams in memory," said the study by Perrine Ruby a research fellow at the Lyon Neuroscience Research Centre in France.

The high-dream recallers also awaken more frequently in their sleep than low-dream recallers.

"The sleeping brain is not capable of memorising new information; it needs to awaken to be able to do that," explained Ruby.

High-dream recallers, both while awake and while asleep, showed stronger spontaneous brain activity in the medial prefrontal cortex (mPFC) and in the temporo-parietal junction (TPJ) - an area of the brain involved in attention orienting toward external stimuli.

This may explain why high-dream recallers are more reactive to environmental stimuli, awaken more during sleep, and thus better encode dreams in memory than low-dream recallers, said the study.

The researchers used Positron Emission Tomography (PET), an imaging technique that uses a radioactive substance, to measure the spontaneous brain activity of 41 volunteers during wakefulness and sleep.

The volunteers were classified into two groups: 21 high-dream recallers who recalled dreams 5.2 mornings per week in average, and 20 low-dream recallers who reported 2 dreams per month in average.

The findings suggest that high and low-dream recallers differ in dream memorisation but do not exclude that they also differ in dream production.

It is possible that high-dream recallers produce a larger amount of dreaming than low dream recallers, added the study published in the journal Neuropsychopharmacology.