The Oddity of Dreams / Study with amnesiacs suggests how brain uses various types of memories
IF PEOPLE CAN'T recall a recent event, will they still
dream about it? According to a new study, the answer-a surprising yes-is
raising a slew of questions about where dreams come from, what they mean and
what role they play in learning and memory.
Dr. Robert Stickgold, a psychiatrist at Harvard Medical School in Boston
and the lead author of the research effort, said the combination of the popular
computer game Tetris and a group of volunteers, including some with amnesia,
has paved the way for future scientific studies of dreams.
"The studies with the amnesiacs have given us for the first time the
ability to look at where in the brain our dreams come from," Stickgold said in
a phone interview. "It's sort of like a 'Where's Waldo?' experiment."
In the study, reported Oct. 13 in the journal Science, Stickgold and his
team spent three days training 27 volunteers to play the computer game Tetris,
which requires spatial reasoning to properly arrange a series of falling
blocks. The study included 10 Tetris experts, 12 novices with no previous
experience and five people with amnesia who had to be retaught the game each
time they played it.
After morning and evening playing sessions on the first two days, 17 of the
volunteers reported dreaming of falling or rotating Tetris blocks in the first
hour of their slumber. To the surprise of the scientists, those dreamers
included three volunteers with amnesia who didn't remember playing the game or
even the researcher who taught them.
Since such sleep-onset dreams commonly contain isolated snippets of recent
experiences, researchers had generally guessed that they originate from
memories of recent episodes stored in the hippocampus, a region deep within the
brain. But people with amnesia brought on by hippocampal damage are unable to
remember recent events. They can, however, remember isolated facts stored as
memories in the brain's outer neocortex layer.
Stickgold said his study results suggest that memories of facts, such as
the shapes and sizes of the Tetris blocks, were the true source of the
sleep-onset visions dancing in the game players' heads. And he predicts the
finding will also hold true for the truly weird dreams we encounter late at
night.
"Part of the reason our dreams are so bizarre and disconnected is that
we're not filtering that through our episodic memories that hold everything
together," he said.
Upon waking from an afternoon nap, for example, one of the volunteers
reported dreaming about Tetris pieces falling onto a garden path. The seemingly
disjointed nature of the image, Stickgold said, is a hallmark of a late stage
of sleep characterized by rapid eye movement and intense dreams.
The dream can be explained, he said, by the brain's attempt to link two
related topics such as ordered game blocks and the ordered nature of landscape
architecture.
"It's like the brain is saying, 'Wait a minute, guys, I know this seems
bizarre and illogical, but it kind of fits together,'" Stickgold said.
Figuring out what to do with incoming data is "probably the most difficult
task that the brain has to perform," he said, a learning process he says is a
critical function of sleep-and dreams.
Among other findings in the study, two of the expert Tetris players
reported dreaming about earlier color versions of the game they had played
instead of the black-and-white version used in the experiment. Stickgold said
their mental association of related images supports his notion that dreams act
as learning aids to process potentially useful information.
Richard Haier, a psychologist in the department of pediatrics at the
University of California at Irvine, called Stickgold's study "very clever" and
"intriguing," although he noted the small study size warrants a degree of
caution when interpreting the results. Haier, who has used Tetris to examine
which regions of the brain are involved in learning a complex task, said the
study raises important questions such as whether drugs that disrupt sleep-onset
dreams could impede the ability to proficiently learn new skills.
For Stickgold, the popularity of power naps and longer siestas is telling
in and of itself.
"Sleeping in general, and dreaming in particular, is giving the brain the
chance to disconnect from recent events and just look at the raw facts," he
said. "It's what we mean when we say, 'I'm going to sleep on it.'"
