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 seven 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. In response to the CPG data, Nedivi and Lee revisited this question with the help of So and Hua
Source:Massachusetts Institute of Technology