A sleeping brain can form fresh
memories, according to a team of neuroscientists. The researchers played
complex sounds to people while they were sleeping, and afterward the sleepers
could recognize those sounds when they were awake. The idea that humans can
learn while asleep, a concept sometimes called hypnopedia, has a long and odd
history. Researchers accomplished pattern learning. While a group of 20
subjects was sleeping, the neuroscientists played clips of white noise. Most of
the audio was purely random but there were patterns occasionally embedded
within the complex noise: sequences of a single clip of white noise, 200
milliseconds long, repeated five times. The subjects remembered the patterns.
The lack of meaning worked in their favor; sleepers can neither focus on what
they're hearing nor make explicit connections, the scientist said. This is why
nocturnal language tapes don't quite work — the brain needs to register sound
and semantics.
But memorizing acoustic patterns
like white noise happens automatically. Once the sleepers awoke, the scientists
played back the white-noise recordings. The researchers asked the test subjects
to identify patterns within the noise. Unless you happened to remember the
repetitions from a previous night's sleep. The test subjects successfully
detected the patterns far better than random chance would predict. What's more,
the scientists discovered that memories of white-noise pattern formed only
during certain sleep stages. When the authors played the sounds during REM and
light sleep, the test subjects could remember the pattern the next morning.
During the deeper non-REM sleep, playing the recording hampered recall.
Patterns presented during non-REM sleep led to worse performance, as if there
were a negative form of learning. This marked the first time that researchers
had evidence for the sleep stages involved in the formation of completely new
memories.
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