NEW YORK (AP) _ Scientists now have an inkling about itching and scratching. They've been able to watch spinal nerves transmit the itch relief signal to the brain in monkeys, a possible first step toward finding new treatments for persistent itching in people. More than 50 conditions can cause serious itching, including AIDS, Hodgkin's disease and the side effects of chronic pain treatment. A researcher at the University of Minnesota in Minneapolis says scratching can lead to serious skin damage and infections. He says scientists want to find ways for people to relieve their distress "without tearing up their skin.'' The federally funded study is reported today on the Web site of the journal Nature Neuroscience.