A recent sleep study shows that when we recall our dreams, we experience the same brainwave activity that we experience when we remember events in waking life.
The results of the study by Cristina Marzano, Michele Ferrara, Luigi de Gennaro and their colleagues at the University of Rome were published in the Journal of Neuroscience in May 2011.
65 students were chosen as subjects for this sleep study.
As the subjects slept, their brainwaves were recorded.
30 of the subjects were awakened during REM sleep, while 35 were awakened during Stage N2 of NREM sleep. (Dreaming occurs during all sleep stages, although the content of REM dreams is usually different from the content of NREM dreams.)
In the morning, the subjects were asked to fill out a diary in which they reported on the quality of their sleep and stated whether they remembered having any dreams, and if so, how many dreams they remembered.
Of the 30 subjects who were awakened during REM sleep, 20 remembered dreaming and 10 did not.
Of the 35 subjects who were awakened during NREM sleep, 20 recalled dreaming and 15 did not.
The study revealed that the type of brain wave activity the subjects exhibited when they were awakened could be used to predict whether they would remember their dreams.
Subjects with higher levels of theta wave activity in the frontal region of the brain when they were awakened during REM sleep were more likely to remember their dreams. As the level of theta wave activity increased, the number of dreams they remembered was also likely to increase.
Theta waves are low frequency waves, with a frequency of about 5 to 7 Hertz (Hz - cycles per second).
When subjects were awakened during NREM sleep, they were more likely to remember their dreams if they had lower levels of alpha wave activity in the right temporal region of the brain. As the level of alpha wave activity decreased, the number of dreams that they were likely to remember increased.
Alpha waves have a frequency of about 8 to 12 Hz.
These brainwave patterns match the same patterns that are used when you create episodic memories - memories of things that happened to you and the feelings that were associated them.
Examples of episodic memories are what how long your commute home from work was yesterday, and what it was like; what happened on your birthday last year and whether you had a good time; and what you had for dinner last Thursday and how it tasted.
It has previously been shown that in waking life, theta wave activity in the frontal area of the brain increases - just as it increases before an REM dream is remembered - when episodic memories are encoded (stored in memory for later recall).
Lower levels of alpha wave activity - as occur before an NREM dream is remembered - are associated with a better ability to encode memories of words and faces and to encode episodic memories.
Increases in alpha wave activity are associated with a decline with the ability to recall waking life memories.
The results of this study indicate that we use the same parts of our brains to remember our dreams that we use to form episodic memories in our waking lives.
It provides support for the Continuity Hypothesis of Dreams, which states that when you dream, you are continuing the thought processes that you have been experiencing in waking life.