January 19, 2006

Lack of sleep leads to fewer brain cells, in rats

By Anne Harding

NEW YORK (Reuters Health) - 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

Lack of adequate sleep is "definitely not good for the
brain in the long run," the investigator told Reuters Health.
"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

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.