It HAS long been accepted as common wisdom that a good nights sleep helps when making an important decision. But now scientists have backed up this notion after finding that one key effect of sleep is facilitating and enhancing complex cognitive skills necessary for decision-making. In one of the first studies of its kind, researchers investigated the effects of sleep on affect-guided decision-making - that is decisions on meaningful topics where subjects care about the outcome. Lead researcher Rebecca Spencer, of the University of Massachusetts Amherst, taught a group of 54 young to play a card game for rewards of play money in which wins and losses for various card decks mimic casino gambling. Subjects who had a normal nights sleep as part of the study drew from decks that gave them the greatest winnings four times more often than those who spent the 12-hour break awake. Those who were rested also better understood the underlying rules of the game. Psychologists believe rule discovery is an often hidden yet key factor that is crucial to making sound decisions. DM