Functional Plasticity in Living Brain

Researchers from MIT have dispelled a commonly held belief that adult brain cells don’t grow, when they discovered remodeling of dendritic arbors in the visual cortex in living mice. The discovery might have future clinical implications.
From the MIT News Office:

The study’s co-authors — Nedivi; Peter T. So, an MIT professor of mechanical and biological engineering; Wei-Chung Allen Lee, an MIT brain and cognitive sciences graduate student; and Hayden Huang, a mechanical engineering research affiliate — used a method called two-photon imaging to track specific neurons over several weeks in the surface layers of the visual cortex in living mice. While many studies have focused on the pyramidal neurons that promote firing, this work looked at all types of neurons, including interneurons, which inhibit the activity of cortical neurons.
With the help of technology similar to magnetic resonance imaging (MRI), but at a much finer, cellular resolution, the researchers were able to stitch together two-dimensional slices to create the first 3-D reconstruction of entire neurons in the adult cortex. Dendritic branch tips were measured over weeks to evaluate physical changes.
What the researchers saw amazed them.
In 3-D time-lapse images, the brain cells look like plants sprouting together. Some push out tentative tendrils that grow around, or retract from contact with, neighboring cells. Dendrite tips that look like the thinnest twigs grow longer. Of several dozen branch tips, sometimes only a handful changed; in all, 14 percent showed structural modifications. Sometimes no change for weeks was followed by a growth spurt. There were incremental changes, some as small as 7 microns, the largest a dramatic 90 microns.
“The scale of change is much smaller than what goes on during the critical period of development, but the fact that it goes on at all is earth-shattering,” Nedivi said. She believes the results will force a change in the way researchers think about how the adult brain is hard-wired.
Nedivi had previously identified 360 genes regulated by activity in the adult brain that she termed candidate plasticity genes or CPGs. Her group found that a surprisingly large number of CPGs encode proteins in charge of structural change. Why are so many of these genes “turned on” in the adult well after the early developmental period of dramatic structural change?
The neuroscience community has long thought that whatever limited plasticity existed in the adult brain did not involve any structural remodeling, mostly because no such remodeling was ever detected in excitatory cells. Yet evidence points to the fact that adult brains can be functionally plastic.

The press release…
The article: Lee WCA, Huang H, Feng G, Sanes JR, Brown EN, et al. (2006) Dynamic Remodeling of Dendritic Arbors in GABAergic Interneurons of Adult Visual Cortex. PLoS Biol 4(2): e29