Scientists have found that when test monkeys spent five minutes learning how to use a rake, some of the neurons that responded to touching their hands began behaving in a new way. They began to fire in response to stimuli at the end of the rake, not on the monkey's hand. Other neurons in the brain respond to things that appear to lie within arm's reach. Training the monkeys to use the rakes caused these neurons to change--reacting to objects lying within rake's reach rather than arm's reach.