Posted by: beagle4 | February 6, 2011

Amnesiacs key to understanding content of dreams

Have you ever played a video game for so long that you started to dream about it? The internet has provided thousands of sites providing extremely addicting games. My personal favorite is Poppit, an online game where you pop colored balloons that are next to each other in an attempt to pop all of the prizes within the balloons. I usually would play this game for hours straight, and when I finally go to sleep I have dreams about popping balloons and performing 5-10 moves shifting the balloons in my head. What type of memory controls the types of content provided in your dreams?

Robert Stickgold (also in the Nova documentary I watched earlier) and his colleagues at Harvard Medical School conducted an experiment in 2000 in an attempt to understand the content of dreams. The experiment set up by Stickgold studied three different sets of subjects (27 total) to play the common game of Tetris over the course of three days. Of the 27 subjects: 12 were beginners and had never played the game before the experiment, 10 were experts who played between 50 and 500 hours of Tetris, and 5 were amensiacs that had no short-term memory due to lesions in the hippocampus. (Amnesiacs can retain new information temporarily, they generally forget it a few minutes later.)

During hypnagogic sleep (transitional state between wakefulness and sleep) the hippocampus stores recent, episodic memories about individual events and replays the information for the neocortex (location of the brain that stores permanent memories). During REM the opposite occurs, information flows from the neocortex back to the hippocampus.

The results of the experiment showed that 17 of the subjects reported seeing the Tetris shapes move and rotate while they slept. In addition, most of these reports occurred after the second night. The beginner players increased their overall  scores drastically as shown from the graph below, and 9 of 12 of which experienced reported seeing falling pieces. However, images of the score, picture surrounding the pieces, and finger placement on the keyboard was not seen during these dreams. Most surprisingly, three of the five amnesiacs described having similar dreams which was not something Stickgold expected. Based off the results, Stickgold believes dreams come from implicit memories and not declarative memory. One class of implicit memory is found in the procedural memory system, which allows you to still be able to ride a bike after years without doing so, and allow you to know where the keys on a keyboard are located without looking. Another type of implicit memory is semantic knowledge which involves general, abstract concepts (the reason why only the tetris shapes and colors were seen).

By dreaming of the game even if it was just about the pieces, the subject was able to increase their score. All it takes is to sleep. This is why most people recommend getting a good night sleep as preparation for a test. Stickgold’s experiment helps identify the content provided in dreams. By analyzing amnesiacs the type of memory content present in dreams has been identified. Although most of the amnesiacs did not remember the game from one day to the next and had to be taught the rules all over again, the Tetris dreams seemed to affect their waking behavior. One even put her fingers on the correct keys before the game, even though they didn’t remember how to play. It is possible that dreams can help play a big role to provide a solution to the disease of amnesia.

I found a video produced in 2010 of Robert Stickgold discussing dreams. It is a long video, so if you are interested I recommend watching from 11:16. In the video Stickgold discusses a similar experiment he conducted with a maze game, as well as an experiment providing a list of words to remember. For both experiments he had two different sets of test subjects: one set took the test hours after hearing the words/playing with the maze, and the other set took the test the next morning after sleeping. The group that slept did better than the group that did not sleep.

On a side note: I found two articles discussing the Tetris experiment, one from Scientific America and one from MSNBC. The Scientific America, a journal focused towards more scientific readers, article provided more insight to the actual experiment conducted, and provided more graphs of the results. On the other hand, the MSNBC, focused on providing news, article focused on more of the overall findings and conclusion of the experiment. It also provided multiple direct quotes from Robert Stickgold. Both articles have different audiences and adjusted their writing style for the audience. Different information about the experiment was revealed based on what the author thought was necessary.

Now just close your eyes and dream…



  1. I have never dreamed about a video game, but I have fallen back asleep after turning my alarm clock off, and thought about not falling back asleep (but always seem to fall back alseep) so much that I woke up to an alarm clock in my dream. Kinda the same thing. Has this ever happened to anyone else?

    • Hm interesting. I’ve had sounds in my dream progressively get louder and louder, and when I finally wake up I realize that the sound was my alarm clock going off. I usually wake up a couple minutes before my alarm clock ever goes off in the morning.

  2. Great post–tons of information and really interesting stuff. I often dream I’m snowboarding after I’ve been snowboarding, and startle awake when I feel like I’m falling. I’m guessing it’s the same principle.

  3. […] recall and evaluate a daily sequence of events during dreams similar to the way humans can. (In a previous post I discussed how humans can learn and recall during dreams with the Tetris experiment.) In the […]

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