Stanford scientists made mice walk in circles via remote control of a wireless LED implanted in the rodents' brains. Switching the LED on and off controls neurons that have been previously genetically engineered to be light-sensitive.
This incredible field, called optogenetics, enables researchers to better understand the function of the brain. These kinds of experiments previously required wired implants or bulky devices worn on the animals' head. From IEEE Spectrum:
The new device, consisting of a power receiving coil, IC, and LED, weighs in at 20 to 50 milligrams (a mouse's head is approximately 2 grams). Its tiny dimensions mean it can be implanted not only in the brain, but also in the spine or the limbs, allowing researchers to experiment with optogenetic stimulation of the spinal cord and peripheral nerves. The researchers note that the implant can be built "with readily available components and tools," and they express hope that it will be quickly adopted by the scientific community.