A 3D light switch for the brain

New device for delivering light to individual neurons could one day help treat Parkinson's disease, epilepsy; aid understanding of consciousness, how memories form
November 21, 2012

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 et al./Optics Letters)

A new fiber-optic device created by MIT biologists and engineers is the first tool that can deliver 1000 precise points of light to a 3D section of living brain tissue matter smaller than a sugar cube.

This is a step forward for a technique called optogenetics, which uses gene treatments to turn individual brain cells on and off with light.



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 et al./Optics Letters)


“You can see neural activity in the brain that is associated with specific behaviors, but is it important?” Boyden says, ” 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.


Targeting neurons with light


Drugs can turn neurons on or off as well, he continues, but not on such a quick time scale or with such a high degree of control. In contrast, the new 3-D array is precise enough to activate a single kind of neuron, at a precise location, with a single beam of light.

In an earlier incarnation, Boyden’s device looked like a needle-thin probe with light-emitting ports along its length; this setup allowed scientists to manipulate neurons along a single line. The new tool contains up to a hundred of these probes in array of microwaveguides, which makes the device look like a series of fine-toothed combs laid next to each other with their teeth pointing in the same direction.




Blue for on, yellow for off

Neurons in the brain are not naturally responsive to light, so scientists sensitize these cells with molecules called opsins — light-detecting proteins such as such as channelrhodopsins naturally found in algae and bacteria. Genes for an opsin are transferred to the neurons in a mouse’s brain using gene therapy, a process in which DNA is ferried into a cell via a carrier such as a harmless virus. The carrier can be instructed to deliver the DNA package only to certain types of cells.




A 3D neural prosthesis




Boyden says his group is excited about the possibility of commercializing the new 3D array, as one potential route that would make the devices available as quickly as possible to the neuroscience community.