Oct. 12, 2000 -- The stuff dreams are made of does not come from one's conscious memories. A clever study showing that people with severe amnesia can have the same dreams as normal people sheds new light on how we dream -- and why.
"What we're really looking at here is the age-old mind/body problem," says Harvard researcher Robert Stickgold, PhD. "We think of our mind as being ours, but there are real ways in which the brain has a set of rules of its own."
Stickgold and co-workers set out to explore the role played by conscious memory systems in the birth of dream images. To do so, they had people play a silent, black-and-white computer version of the game Tetris, which calls for a player to rotate blocks of various shapes and to fit them into place at an ever-faster pace. Each person played the game two hours a day for three days. Each night -- just as the players were falling asleep -- a researcher woke them and asked what they were seeing.
Three groups of players participated in the study. The first two groups were healthy people -- 12 who were new to the game and 10 who had played it many times before. Most interesting, however, was the third group: five people with amnesia. These patients have extensive damage to the parts of the brain responsible for conscious memory. Experts call this episodic or declarative memory -- the kind of memory that allows one to remember whether one saw a bicycle the day before. The amnesia patients, however, have intact procedural memory -- the kind of unconscious memory that allows one to remember how to ride a bicycle.
The players with normal memories got much better at playing the game. The people with amnesia did not. This suggests that Tetris skill involves conscious memory but not procedural memory. But when waked, the amnesia patients were just as likely to report seeing falling Tetris blocks as the healthy novice players -- even though they had no conscious memory of ever having played the game. What makes this particularly striking is that the players were waked just as they were falling asleep. During this very early period of sleep, people feel as though they are awake. Indeed, dreams that occur during this time are called hypnagogic hallucinations to distinguish them from the generally more surreal dreams that occur in later sleep. "We thought if there's one part of sleep that depends on episodic memories -- which amnesiacs lack -- it is sleep onset," Stickgold says.
These results suggest that the images one sees during dreaming have nothing to do with conscious memory. Another finding supports this conclusion -- most of the Tetris players who saw falling Tetris blocks in their dreams did so not on the first day of play, but on the second day. Moreover, some of the expert Tetris players saw falling blocks in color with music playing -- just as they did when they played a different version of the game years before.
The study provides the best experimental support yet for the theory that dreams arise as the sleeping brain -- without help from the conscious mind -- strengthens the connections between different brain circuits that were created during learning. Because the players remembered only the falling blocks, and not the computer keyboard or other details unimportant for learning the game, the study also suggests that the brain strengthens only those circuits that appear to be most appropriate.
"In the process of reinforcing those circuits, their contents intrude on our awareness while we sleep -- in a nutshell, that's why we dream," Lee J. Kavanau, PhD, tells WebMD. "Our dreams are simply the contents of circuits that are activated. Most researchers believe that there is no method to it. Dreams don't necessarily serve any specific function -- but that doesn't mean that what's in them doesn't have any significance." Kavanau, emeritus professor at the University of California at Los Angeles' department of organismic biology, ecology, and evolution, did not participate in the Harvard study.
Michael Schredl, PhD, a sleep researcher at the Central Institute of Mental Health in Mannheim, Germany, was present when Stickgold earlier this year presented his findings at a conference of his peers. "Most people think that dreaming has to do with memory, and that the pictures of the dream are images that relate to waking-life experience," Schredl tells WebMD. "Therefore, it may be surprising if you ask a person about their waking-life experience and they don't remember it, but find that they can dream about it. On the other hand, when you work with people such as sexual abuse victims in early childhood, you can see that the images in dreams can reflect things that the person is not consciously aware of -- people dream of things they cannot remember in waking life. The dream memory system is not the same that the waking consciousness has access to."
Schredl says his work convinces him that dreaming is a holistic experience that involves far more than the conscious mind. He sees support for this idea in the Harvard study. "I think this study is quite in line with the idea that a dream is a holistic experience, not just the reproduction of declarative memory," he says. "Research shows that emotionally salient things for a person's life are reflected in dreams. If you use dreams in psychotherapy, you can help a person understand his or her life better."