Researchers in the United States have developed a new method for controlling the brain circuits associated with complex animal behaviours, using genetic engineering to create a magnetised protein that activates specific groups of nerve cells from a distance. The new technique ... is not only non-invasive, but can also activate neurons rapidly and reversibly. Several earlier studies have shown that nerve cell proteins which are activated by heat and mechanical pressure can be genetically engineered so that they become sensitive to radio waves and magnetic fields. The new technique builds on this earlier work, and is based on a protein called TRPV4, which is sensitive to both temperature and stretching forces. These stimuli open its central pore, allowing electrical current to flow through the cell membrane; this evokes nervous impulses that travel into the spinal cord and then up to the brain. In one final experiment, the researchers injected Magneto into the striatum of freely behaving mice ... and then placed the animals into an apparatus split into magnetised a non-magnetised sections. Mice expressing Magneto spent far more time in the magnetised areas than mice that did not, because activation of the protein caused the striatal neurons expressing it to release dopamine, so that the mice found being in those areas rewarding. This shows that Magneto can remotely control the firing of neurons deep within the brain, and also control complex behaviours.