Combining optogenetics and wireless energy transfer technology, a new device is said to be the first fully implantable platform for optical neural stimulation. The device dramatically expands the scope of optogenetics research to include experiments involving mice in enclosed spaces or interacting freely with other animals, according to researchers at Stanford University. "This is a new way of delivering wireless power for optogenetics," said professor Ada Poon. "It's much smaller, and the mouse can move around during an experiment … I think other labs will be able to adapt this for their work." Traditionally, optogenetics has required a fiber optic cable attached to a mouse's head to deliver light and control nerves. With this somewhat restrictive headgear, mice can move freely in an open cage but can't navigate an enclosed space or burrow into a pile of sleeping cage-mates the way an unencumbered mouse could. Also, before an experiment, a scientist has to handle the mouse to attach the cable, stressing the mouse and possibly altering the outcome of the experiment. These restrictions limit what can be learned through optogenetics, which involves genetically altered light-sensitive proteins that can alter and control neural functions. The approach has been used to investigate a range of scientific questions including how to relieve tremors in Parkinson's disease, the function of neurons that convey pain and possible treatments for stroke. However, addressing issues with a social component like depression or anxiety, or that involve mazes and other types of complex movement, is more challenging when the mouse is tethered. Wireless energy transmission could allow researchers to cut these tethers. In recent experiments, the Stanford team used a novel, 16-cm-wide stage emitting radio-frequency (RF) energy to power an optogenetic device implanted in a mouse's leg. The RF signal is tuned to a frequency that resonates in mouse bodies but it is effectively trapped inside the cavity by a grid with subwavelength holes. When a mouse is placed on top of the grid, however, its body becomes a conduit for the energy, transmitting it to a 2-mm coil inside the implanted device. Wherever the mouse moves, its body comes in contact with the energy, drawing it in and powering the device. Elsewhere, the energy stays contained. In this way, the mouse becomes its own localizing device for power delivery. The work was published in Physical Review Applied (doi: 10.1103/PhysRevApplied.4.024001) and Nature Methods (doi: 10.1038/nmeth.3536). For more information, visit www.stanford.edu.