In a lab in Oxford University's experimental psychology department, researcher Roi Cohen Ka-dosh is testing a relatively new brain-stimulation technique which may help people learn and improve their understanding of math concepts. The electrodes(a small piece of metal or other substance that is used to take an electric current)are【C1】______in a tightly fitted cap and worn around the head. The device, run off a 9-volt battery commonly used in smoke detectors, induces only a【C2】______current and can be targeted to【C3】______areas of the brain or applied generally. The mild current reduces the【C4】______of side effects, which has【C5】______possibilities about using it, even in individuals【C6】______a disorder, as a general cognitive【C7】______. Scientists also are investigating its use to treat mood disorders and【C8】______conditions. Dr. Cohen Kadosh's【C9】______work on learning enhancement and brain stimulation is one example of the long journey faced by scientists【C10】______brain-stimulation and cognitive-stimulation techniques.【C11】______other researchers in the community, he has dealt with public【C12】______about safety and side effects, plus【C13】______from other scientists about whether these findings would hold in the wider population. There are also ethical questions about the technique.【C14】______it truly works to enhance cognitive performance, should it be【C15】______to anyone who can afford to buy the device—which already is【C16】______for sale in the U.S.? Should parents be able to perform such stimulation on their kids without【C17】______? "It's early days but that hasn't stopped some companies from【C18】______the device and marketing it as a learning tool," Dr. Cohen Kadosh says. "Be very【C19】______." However, if the technique continues to show【C20】______, "this type of method may have a chance to be the new drug of the 21st century," says Dr. Cohen Kadosh.