( determine how long it would take them t...)Mice brains shrink during winter, impairing some learning and memory

Results showed that mice that were kept in short days ?simulating winter ?took longer and swam farther before they found the hidden platform than did the long-day mice, indicating they had more trouble learning where the platform was. Moreover, they didn't remember its location as well from one day to the next.

However, other tests showed that nonspatial learning and memory, including sensory abilities, were not affected by short days.

"It appears that only specific kinds of brain function are impaired during winter," Nelson said.

In a second experiment, 16 adult male white-footed mice were kept in short or long days for 14 weeks, after which they were sacrificed. The researchers then examined differences in the brains between mice kept in the two differing conditions.

These results showed that mice kept in short days had on average a smaller brain mass compared to the other mice, even when taking into account that their overall body mass was smaller, too.

In addition, the researchers found changes in a region of the brain ?the hippocampus ?that is involved in spatial memory. Mice in short days had a proportionally smaller hippocampus, as well as changes in spine density there that have been associated with spatially related memory and learning performance.

"We predicted that when you reduce the size of the hippocampus, it would have an impact on learning, and that's what we found," Nelson said.

The shrinking of the brain corresponds to a season when the mice may have less need for spatial memory, Nelson said.

"They don't maintain as large a territory in the winter," he said.

Nelson said he and his colleagues believe it may be the hormone melatonin which controls the changes in brain size and function in mammals such as these white-footed mice. Scientists know t
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Source:Ohio State University