Wireless, implantable device that stimulates nerves

Scientists have developed a wireless, implantable device that delivers light to stimulate nerves in mice, an advance that may lead to improved treatments for mental health diseases and movement disorders.
The miniature device that combines optogenetics - using light to control the activity of the brain - with a newly developed technique for wirelessly powering implanted devices is the first fully internal method of delivering optogenetics.
Optogenetics has required a fibre optic cable attached to a mouse's head to deliver light and control nerves. With this restrictive headgear, mice can not navigate an enclosed space or burrow into a pile of sleeping cage-mates the way an unencumbered mouse could.

"This is a new way of delivering wireless power for optogenetics. It's much smaller and the mouse can move around during an experiment," said Ada Poon, an assistant professor of electrical engineering at Stanford University.
Poon decided to use the mouse's own body to transfer radio frequency energy that was just the right wavelength to resonate in a mouse.
Poon had the idea but initially didn't know how to build a chamber to amplify and store radio frequency energy. She and Yuji Tanabe, a research associate in her lab, then travelled to Japan to do the initial assembly and testing.

In its native state the open chamber would radiate energy in all directions. A grid was overlaid on top of the chamber with holes that were smaller than the wavelength of the energy contained within. That trapped the energy inside the chamber.

The key is that there's a bit of wiggle room at the grid. So if something like, say, a mouse paw were present, it would come in contact with the boundary of all that stored energy.
The mouse essentially becomes a conduit, releasing the energy from the chamber into its body, where it is captured by a 2 mm coil in the device.

Wherever the mouse moves, its body comes in contact with the energy, drawing it in and powering the device.
The device is the first attempt at wireless optogenetics that is small enough to be implanted under the skin and may even be able to trigger a signal in muscles or some organs, which were previously not accessible to optogenetics.
Optogenetics only works on nerves that have been carefully prepared to contain the proteins that respond to light.
In the lab, scientists either breed mice to contain those proteins in select groups of nerves or they carefully and painstakingly inject viruses carrying the protein DNA into nerves the size of dental floss.

Shining a light - whether through a fibre optic cable or a wireless device - on neurons that haven't been prepared has no effect.
The team said the device and the novel powering mechanism open the door to a range of new experiments to better understand and treat mental health disorders, movement disorders and diseases of the internal organs.
The study is published in the journal Nature Methods.