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Wireless Light-Activated Circuit Connects to Mice Neurons

Mouse with optogenetic system

Mouse with optogenetic system, illuminated in blue light, on hind leg. (Ada Poon, Stanford University)

17 August 2015. Engineers at Stanford University designed a wireless circuit implanted under the skin for sending light-activated signals to nerve cells in lab mice. The team led by electrical engineering professor Ada Poon published its findings in today’s issue of the journal Nature Methods (paid subscription required).

Poon and colleagues are seeking a simple, self-contained technique for sending electrical signals to the brain and nervous systems with optogenetics, the use of light energy to influence activities of genes sensitive to light, with a miniaturized power source. Current methods for using optogenetics requiring connecting a fiber optic cable to a device attached to the animal’s head, which limits the range and affects the behavior of the animals.

The team from Poon’s lab and others at Stanford applied their previous work with wireless power systems for medical implants, reported last May in Science & Enterprise. Those systems send power wirelessly to a tiny power harvester and battery coupled to the implant, which can make heart pacemakers as small as a grain of rice.

For optogenetics, however, the researchers also need to track the location of the recipient to be able to transfer power, as well as deliver the power in the right wave length for the mouse. For locating the mouse, the researchers built a permeable top layer on the chamber holding the mice that traps the energy inside. A grid on the top layer acts like a sensor that tracks the mouse’s movement from one quadrant to the next. The mice were bred to express proteins in the skin to respond to light.

To find a consistent wave length for transmitting the energy, the team in effect harnessed the mouse’s own nervous system, connecting the brain, spinal cord, and peripheral nerve endings. Power is also stored in a miniature (2 millimeter) coil. As the mouse moves through the chamber, its location is noted on the grid, where the system — small enough to be implanted under the skin in the mouse’s leg — wirelessly draws in the radio-frequency power.

The system is modular to enable researchers to reconfigure it for various applications, and Poon’s lab is making the power source available for other labs.  “This is a new way of delivering wireless power for optogenetics,” says Poon in a university statement. “I think other labs will be able to adapt this for their work.”

The researchers alerted Stanford’s technology transfer office that the system has commercial potential for therapeutic applications, making it eligible for patent protection and licensing. Poon and colleagues already plan to investigate applying the technology  as a therapy for chronic pain, and received a grant from Bio-X institute for that work Other applications are treatments for mental health disorders, movement disorders, and diseases of internal organs that respond to electronic stimulation.

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