Flexible Fiber Probes Enable Spinal Activity Stimulation and Recording

Achievement date: 
2015
Outcome/accomplishment: 

An MIT team demonstrated for the first time the simultaneous optical stimulation and neural recording of activity in the spinal cord of mice using flexible fiber probes. The research was conducted through the Center for Sensorimotor Neural Engineering (CSNE), an NSF-funded Engineering Research Center (ERC) with headquarters at the University of Washington.

Impact/benefits: 

Restoring motor and sensory functions in people who are paralyzed requires tools for real-time recording and stimulation of neural activity in the spinal cord. The successful use of the fiber probes is a step toward restoring motor function and uses optogenetics, a technology for controlling neural activity with light. 

Explanation/Background: 

The spinal cord presents technical challenges in its flexible, fibrous structure and repeated elastic deformation during normal motion. Developing fibers that are flexible and that will continue transmitting a signal amid a twisting and bending spine remains a key challenge to developing prostheses for injured spines. That’s particularly true of fibers that might carry optical signals through the spine, as most neural probes and light-delivery devices are comprised of brittle materials.

The probes developed under the direction of MIT Professor Polina Anikeeva are almost as thin as human hairs and flexible enough to be tied in a knot. They continued to work even when bent more than 180 degrees, which is more than the movements of a yoga instructor. The probes are fabricated using a thermal drawing process, the same technology that is used to create optical fibers.

The technology is not yet transferrable to humans, whose spinal neurons are not sensitive to visible light. The study relied on mice whose genes had been modified to develop neurons that can express light-sensitive ion channels. But the probes can be inexpensively reproduced, are made entirely of biocompatible materials, and also open the door to create a “next generation” of neural prosthetics—including perhaps combining the probes with a prosthetic limb in a way that blurs the line between the human and the bionic.