Knowing that spatial learning triggers production of new brain cells in the hippocampus, Hairston and her team wanted to find out whether restricting sleep during a spatial learning task would affect new cell production in the hippocampus.
The experiment: swimming to the exit platform
The researchers trained rats on one of two tasks using a water maze -- a plastic pool about six feet in circumference and two feet deep. Rats were placed in the water and had to swim to the exit platform.
One group could not see the platform, which was placed underwater, and had to form a "mental map" of the maze -- a spatial memory task that is hippocampus-dependent -- to quickly reach the exit.
The second group could see and smell the exit platform, which had a citrus odor. The researchers moved the platform every fourth trial, requiring the animal to rely on its senses, not on memory, to find it. This task did not engage the hippocampus because the rat did not need a mental map of the pool to reach the platform, Hairston explained.
Fewer brain cells for the weary
At the end of each training session, half the animals in each group were kept awake for six hours by being presented novel stimuli that kept them interested and awake. The other half were returned to their cages and allowed to sleep. After six hours, the sleep-restricted rats were allowed to sleep for the remainder of the day until the next session, 18 hours later.
Rested animals that had to rely on memory to find the goal showed increased neurogenesis in the hippocampus compared with animals that could use sight and smell. That made sense, because
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Source:American Physiological Society