A 3-D Light Switch for the Brain
A new tool for neuroscientists delivers a thousand pinpricks of light to a chunk of gray matter smaller than a sugar cube. The new fiber-optic device, created by biologists and engineers at the Massachusetts Institute of Technology (MIT) in Cambridge, is the first tool that can deliver precise points of light to a 3-D section of living brain tissue. The work is a step forward for a relatively new but promising technique that uses gene therapy to turn individual brain cells on and off with light.
Scientists can use the new 3-D “light switch” to better understand how the brain works. It might also be used one day to create neural prostheses that could treat conditions such as Parkinson’s disease and epilepsy. The researchers describe their device in a paper published today in the Optical Society’s (OSA) journal Optics Letters.
The technique of manipulating neurons with light is only a few years old, but the authors estimate that thousands of scientists are already using this technology, called optogenetics, to study the brain. In optogenetics, researchers first sensitize select cells in the brain to a particular color of light. Then, by illuminating precise areas of the brain, they are able to selectively activate or deactivate the individual neurons that have been sensitized.
Ed Boyden, a synthetic biologist at MIT and co-lead researcher on the paper, is a pioneer of this emerging field, which he says offers the ability to probe connections in the brain.
"You can see neural activity in the brain that is associated with specific behaviors," Boyden says, “but is it important? Or is it a passive copy of important activity located elsewhere in the brain? There’s no way to know for sure if you just watch.” Optogenetics allows scientists to play a more active role in probing the brain’s connections, to fire up one type of cell or deactivate another and then observe the effect on a behavior, such as quieting a seizure.
Unlike the previous, 1-D versions of this light-emitting device, the new tool delivers light to the brain in three dimensions, opening the potential to explore entire circuits within the brain. So far, the 3-D version has been tested in mice, although Boyden and colleagues have used earlier optogenetic technologies with non-human primates as well.
