The researchers located mirror neurons in the brains of two monkeys, which fired when the monkeys grabbed a small metal object and when they watched the experimenter do the same. Unexpectedly many of these neurons actually had a preference for where the experimenter was grabbing the object — about a fourth of the cells fired more rapidly when the action took place within arm's reach of the monkey (its "peripersonal" space), while another fourth were more excited when the action was out reach (its "extrapersonal space"). Over a range of distances, the closer the motion was to the monkey, the faster its peripersonal mirror neurons fired; the extrapersonal mirror neurons had the opposite response.