Researchers at the University of Pittsburgh have developed an ultra-small implantable neural stimulation device that can be activated using a laser and which doesn’t require a cable that tethers it to a controller outside the body. The researchers hope that the device could pave the way for less invasive neural stimulation therapy in neurological disorders and help scientists to explore neural circuits in the brain.

Neural stimulation therapy involves electrically stimulating neurons to produce a therapeutic effect, and it holds potential in treating neurological disorders such as Parkinson’s disease. The technique is an emerging technology, but one of the major issues preventing its application is the need to have a cable connecting the implanted electrode to an external controller.

“Typically, with neural stimulation, in order to maintain the connection between mind and machine, there is a transcutaneous cable from the implanted electrode inside of the brain to a controller outside of the body,” said Takashi D. Y. Kozai, a researcher involved in the study. “Movement of the brain or this tether leads to inflammation, scarring, and other negative side effects. We hope to reduce some of the damage by replacing this large cable with long wavelength light and an ultra-small, untethered electrode.”

The researchers chose to exploit the photoelectric effect, which changes the electrical potential of an object it strikes, rather than use traditional implantable electrodes. It involves using a near-infrared laser to strike a small untethered electrode in the brain, which can then stimulate nearby neurons. The carbon fiber electrode is only 7–8 microns in diameter, meaning that it is close to the size of a neuron.

“We discovered that photostimulation is effective,” said Kaylene Stocking, another researcher involved in the study. “Temperature increases were not significant, which lowers the chance of heat damage, and activated cells were closer to the electrode than in electrical stimulation under similar conditions, which indicates increased spatial precision.”

The technique is more specific than conventional electrodes, meaning that the effects may be more predictable and controllable. “What we didn’t expect to see was that this photoelectric method of stimulation allows us to stimulate a different and more discrete population of neurons than could be achieved with electrical stimulation,” said Kozai. “This gives researchers another tool in their toolbox to explore neural circuits in the nervous system.”

The researchers are progressing this technology with a view to developing less invasive neural stimulation approaches that can reach deeper tissues. Another application involves wireless on-demand drug delivery.