Scientists have gotten a step closer to making brain transplants a reality by implanting a human gene into mice.
The study looked at how "humanizing" brains of different species affect key cognitive functions. The human gene implanted in mice is associated with language and helped the rodents find food faster than mice without the gene.
Scientists tested hundreds of mice genetically engineered to carry the human version of Foxp2. In a 2009 study, the mice carrying the gene developed more complex neurons and more efficient brain circuits.
In the new study led by Christiane Schreiweis and Ann Graybiel of MIT, researchers trained mice to find chocolate in a maze. Each mouse could do so using two options — to use landmarks like lab equipment and furniture that is visible from the maze, or by the feel of the floor. The mice implanted with the gene learned the route in seven days as well as regular mice did in 11 days.
After removing the landmarks around the maze, the scientists found that the regular mice performed as well as the humanized ones by only learning through the feel of the floor. The same was found when the textiles were removed and only the landmarks were present. The humanized mice only excelled when both learning techniques were present.
Graybiel says this occurs because the human gene increases the cognitive flexibility in mice. This means it lets the brain switch between declarative learning ("turn left when you see the red chair") and procedural or unconscious remembering ("go right when you feel carpeting").
"No one knows how the brain makes transitions from thinking about something consciously to doing it unconsciously," Graybiel said. "But mice with the human form of Foxp2 did much better."
This study may provide some insight into the way, for example, children learn to speck. They seamlessly transition from mimicking words being taught to them to speaking automatically. The study suggests that Foxp2 is the key to being able to switch between declarative and procedural memory, as the mice did during the maze.
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