Skimping on sleep can slow certain types
of learning, a new study in rats shows, and the difficulty
seems to arise from a lack of new brain neurons.
Rodents that got half their normal amount of shut-eye
had a harder time remembering how to navigate a maze than
well-rested rats, Dr. Ilana Hairston of the University
of California at Berkeley and colleagues found.
And while new neurons sprouted and survived in a part
of the brain associated with spatial learning in the animals
that trained in the maze and then slept adequately, this
increased growth of brain cells didn't happen in the sleep-restricted
animals, Hairston and her team report in the Journal of
Neurophysiology.
Lack of adequate sleep is "definitely not good for the
brain in the long run," the investigator stated. "It slows
learning."
Researchers had previously shown that limiting sleep
impairs learning that depends on the hippocampus, a section
of the brain at work in mastering spatial tasks. Past
investigators also had demonstrated that when hippocampal
learning occurs, the survival of new brain cells there
is increased.
Hairston and her colleagues set out to investigate whether
slower learning linked with restricted sleep was related
to reduced neuron survival.
Rats underwent a four-day training in a water maze. Because
the exit was hidden, the animals had to rely on their
memories to find their way out. Half of the rodents were
kept awake for half of the time that they would normally
be asleep -- a condition meant to approximate the low-level
sleep deprivation many people experience in daily life.
The animals that slept less learned more slowly, and
didn't show increased neuron survival in the hippocampus.
But they fared better than the rested rats on a different
type of maze task, in which the exit was visible, marked
out with a citrus scent, and moved for every fourth run
through the maze.
The sleep-deprived animals did better because they relied
on their senses, rather than their spatial memories, to
solve the maze, Hairston said.
She and her colleagues say this suggests that special
techniques could be developed to help chronically sleep-deprived
people, such as members of the military or medical students,
learn more easily. "That said, while the cognitive impairment
may be overcome, our findings indicate that mild, chronic
sleep restriction may have long-term deleterious effects
on neural function," they conclude.
In other words, Hairston said, "You need both experience
and a good sleep afterwards in order to have neurogenesis."
SOURCE: Journal of Neurophysiology, December 2005.
