When the team compared the photos across the months, they observed new spines emerging in response to the beads' placement or learning to run on the wheel. They saw, too, that as the mice became improved at spinning the wheel, a minute fraction of new spines continued to persist. The researchers also noted that at the same time as these new and lasting spines were created, a corresponding number of older spines that had been formed early in the animals' development before the experiment began, disappeared.
Despite the rise and fall of dendritic spines, the animals' brain circuitry remained overwhelmingly secure. A mouse neuron can carry ten thousand spines on its dendrites. Over months, only tens of spines were either gained or lost on each nerve cell after exposure to new experience while the majority of existing spines are maintained.
The study gives a clue as to how it is possible for humans, who have hundreds of thousands of spines on one neuron, to live each day, constantly experiencing and learning new things, without losing existing memories. "The brain is a dynamic and stable organ," says Dr. Gan.
|Contact: Dorie Klissas|
NYU Langone Medical Center / New York University School of Medicine