If you are puzzled over why we remember some dreams but not others, you can blame it on your brain mechanism.
According to Luigi De Gennaro at the University of Rome, Italy, it is the brain mechanism that controls whether we remember or forget things when we are awake is involved.
To test it De Gennaro and his team used an electroencephalogram (EEG) to monitor the brain activity of 65 students as they slept: 30 who habitually wake up while in rapid eye movement (REM) sleep, and 35 who usually wake in stage 2 non-REM sleep. About two-thirds of both groups recalled dreams during the study.
Those who woke during REM sleep and successfully recalled their dreams were more likely to demonstrate a pattern of EEG oscillations called theta waves in frontal and prefrontal cortex areas - the parts of the brain where our most advanced thinking occurs.
"The kind of EEG oscillations and the cortical region involved are the same as those important for recalling memories in awake subjects," New Scientist quoted De Gennaro as saying.
In non-REM wakers, those who remembered their dreams had patterns of alpha wave activity in the right temporal lobe - involved in recognising emotional events - that resembled activity known to be key for recall while awake.
The upshot is that even when we are asleep, the same parts of our brains are on the alert for things to remember. These are often events that are emotionally charged and that the brain deems important, whether we are awake or not.
De Gennero said the results are the first evidence that the physiology by which memories are stored is the same whether we are awake or asleep.
The study has been published in the Journal of Neuroscience.