Researchers at Medtronic are developing a prototype neural implant that uses light to alter the behavior of neurons in the brain. The device is based on the emerging science of optogenetic neuromodulation, in which specific brain cells are genetically engineered to respond to light. Medtronic, the world’s largest manufacturer of biomedical technologies, aims to use the device to better understand how electrical therapies, currently used to treat Parkinson’s and other disorders, assuage symptoms of these diseases. Medtronic scientists say they will use the findings to improve the electrical stimulators the company already sells, but others ultimately hope to use optical therapies directly as treatments.
Light therapy: A neuron (green) engineered to express a light-sensitive protein fires in response to specific wavelengths of light. A glass electrode (lower left corner) records the neuron’s electrical response. Researchers from Medtronic used this system to confirm that a new implantable stimulator can properly activate neurons with light.
Today’s neural implants work by delivering measured doses of electrical stimulation via a thin electrode surgically inserted through a small hole in a patient’s skull, with its tip implanted in a localized brain area.
In the last few years, scientists have developed a way to stimulate neurons using light rather than electricity. Researchers first introduce a gene for a light-sensitive molecule, called channelrhodopsin 2 (ChR2), into a specific subset of neurons. Shining blue light on these neurons then causes them to fire. One advantage of this approach is its specificity–only the neurons with the gene are activated. It also provides a way to shut neurons off–introducing a different molecule, halorhodopsin (NpHR), silences the cells in response to yellow light. “That’s the other unique thing about this approach,” says Tim Denison, senior IC engineering manager in Medtronic’s neuromodulation division. “It allows us to silence neurons’ activity, which is extraordinarily difficult with electrostimulation.”
While academic scientists are developing new tools to deliver light to the brain, Medtronic is developing an optogenetically based implant for commercial use. The module, which is approximately the size and shape of a small USB flash drive, has wireless data links, a power management unit, a microcontroller, and an optical stimulator. It uses a fiber-optic wire to direct light from a blue or green LED at target neurons in the brain.