In the past few years, neuroscientists have shown that the adult brain can do something once thought impossible: grow new neurons. But one area of the brain--the neocortex, the site of most complex mental tasks--still seemed incapable of such regeneration. Now, a study shows that fresh neurons can appear in the mature neocortex too, at least when existing ones die.
In March, neuroscientist Jeffrey Macklis of Harvard Medical School in Boston reported that cell death, of all things, could foster healing. When Macklis destroyed neurons in an area of the brain that helps zebra finches sing, he found that new neurons were born (ScienceNOW, 3 March). But this so-called neurogenesis happened in a species and a part of the brain where the brain cells regrow seasonally, Macklis points out.
The next question, Macklis says, was "Could we induce [neurogenesis] where it does not normally occur?" His team focused on the mouse neocortex. As they did with the zebra finches, the researchers chemically forced some neurons to self-destruct. Then they tracked the development of new neurons with a tracer chemical that labels dividing cells. The neocortex of treated animals contained neurons in all stages of development: Some were just being born, while others were migrating from the subventricular zone. Some were fully mature and had hooked up with their more established neighbors.
"This work shows that the brain has the capacity to respond to damage by repairing itself," says neuroscientist Elizabeth Gould of Princeton University. If similar repair of brain neurons can be triggered in humans, she says, the findings could theoretically open the door for treatments of brain and spinal cord damage.