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Optics Letters 3-D array
A scanning electron microscope image of the 3D array with closeup of a single light-emitting probe. The closeup reveals several light ports along the probe’s edge. Credit: A.N. Zorzos, J. Scholvin, E.S. Boyden, and C.G. Fonstad/Optics Letters.

In a project bridging genetics and engineering, researchers at MIT have created a 3-D fiber-optic neural interface that, combined with a specialized form of gene therapy called optogenetics, can turn individual neurons on and off in a living animal. A powerful new tool for neuroscientists to study and manipulate the brain, the technology may eventually be adapted to act as a neural prosthesis to treat neurological conditions.Optogenetics is a recent but rapidly expanding field synthesizing optics, genetics, and neuroscience. Neurons, in this case in mouse and nonhuman primate brains, are genetically modified to manufacture proteins that respond to a brief flash of laser light guided down an optical fiber. Effectively this means scientists can manipulate brain activity in living animals, but up till now each fiber could only stimulate one 1-D point in the brain.

The new device is a square array of a hundred thin needles, each of which can emit light at several different ports along it’s length; each needle is only 150 microns across, about half the diameter of the average human hair. It can even transmit more than one wavelength of light at the time, which combined with optogenetic techniques means neurons can be both turned on and shut down as researchers choose. Different types of neurons can even be selectively manipulated by modifying them to respond to different wavelengths. Researchers can create any pattern of light they want within the cubic centimeter of the array, using it’s several hundred independent illumination points.

Optics Letters 3-D array light ports illuminated
Optical image of the 3D array with individual light ports illuminated. The array looks like a series of fine-toothed combs laid next to each other with their teeth pointing in the same direction. Credit: A.N. Zorzos, J. Scholvin, E.S. Boyden, and C.G. Fonstad/Optics Letters.

The clinical possibilities of this new device are tantalizing, especially given the extreme level of control that can be exercised over what neurons are affected. Many disorders, such as epileptic seizures, could be treated exactly where they occur in the brain without the side effects of drugs. Despite this, the technology needs to be explored more before any clinical trials can begin. It is not clear yet if the body will detect and reject the modified proteins in the long run.

“It’s turning out to be a very powerful and convenient tool,” said Clifton Fonstad, a professor of electrical engineering at MIT and co-lead author of the paper on the device. Demand for the new tool is too high for the team at MIT to meet, but they say they are excited at the possibility of commercializing the array to make it available as quickly as possible to other researchers.

By Andrew Mathau