THE ROUGH GUIDE TO PSYCHOLOGYfinding food. Neurons in the hippocampus that fired together during the
foraging task also fired together as the rats slept, as if the rodents were
rehearsing their earlier discoveries.
But the sleeping brain doesn’t just store away all your memories, it
seems to judiciously select and preserve those that are most important.
Consider a study published in 2008 by Jessica Payne and her colleagues
at Harvard University. They tested students’ memories for neutral
objects (such as a car) and emotional ones (a crashed car) set against
neutral backgrounds (for example a street scene). Consistent with past
research, they found that emotional objects were remembered better
than neutral objects – in both cases at the expense of memory of the
neutral backgrounds. But after a twelve-hour delay spent awake, although
the advantage for emotional objects over the neutral backgrounds
remained, the memory for both declined significantly. However, it was
a different story after a twelve-hour delay spent asleep. In this case,
memory for the emotional objects, but not the backgrounds, remained
entirely preserved. In other words, sleep seems to consolidate emotional
information far more than neutral material.
As the evidence has accumulated showing how important sleep is for
memories, the search has turned towards finding a way to boost these
natural processes. The first success was reported late in 2009 by John
Rudoy and colleagues at Northwestern University. They had students
learn the locations of fifty objects on a computer screen. As the objects
appeared they were accompanied by an appropriate sound – a cat
with a meow, a kettle with a whistle. Next the students slept and the
sounds of some of the objects were replayed. Re-tested upon waking,
the students performed much better for the objects cued during sleep
than for un-cued objects, even though their pre-sleep performance
for the two groups of objects had been the same. The noise cuing had
no such benefit when the exercise was repeated with the students just
sitting quietly rather than sleeping, thus suggesting the researchers
really had tapped into sleep-based memory processing. Look out for the
appearance of commercial versions of these kinds of memory-boosting
exercises sometime soon!
WHEN SLEEP GOES WRONG
Like everything else, sleep sometimes goes wrong. Perhaps the most
striking example of this is what’s known as “sleep-related automa-
tism” – a form of sleepwalking disorder. Usually when we’re asleep