Electrical simulation therapy affords some relief to the physical dysfunction experienced by spinal cord injury patients or those with prosthetic limbs. However, the ability to precisely target muscle groups is limited and the treatment can be painful.

An alternative therapy in the form of optogenetic stimulation is being pursued by MIT researchers. The Schematic depicting closed-loop experimental paradigm. Source: MITapproach relies on nerves genetically engineered to express opsins, or light-sensitive algae protein, which control electrical signals, such as nerve impulses, when subjected to specific wavelengths of light.

When the proteins were expressed in leg nerves of engineered animal models, researchers governed ankle joint motion by activating an LED implanted in the limb or attached externally. Such closed-loop systems modify their stimulation in response to signals from the nerves being activated; open-loop systems don’t respond to feedback from the body.

The feedback included the joint angle and changes in muscle fiber length. The process also reduced fatigue during cyclic motion by stimulating smaller axons first and then triggering larger fibers, reversing the activation order common in electrical stimulation.

With continued research and clinical trials, an initial application might be to restore motion to paralyzed limbs or to power prosthetics. Optogenetic technology has the potential to restore limb sensation and prevent unwanted pain signals, and could be harnessed for use with therapeutic robotic exoskeletons.

The research is published in Nature Communications.