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It’s not only Hollywood detectives who have hunches; most, if not all, experienced clinicians must be familiar with the situation in which they feel sure that a certain course of action is the right one but are unable to explain why. Much as we may strive towards evidence-based medicine clinical intuition can not be ignored. Now research neuropsychologists in Iowa (Antoine Bechara and colleagues, Science 1997;275:1293-5) have given scientific respectability to the concept of valid but non-rational decision making. Their experimental subjects were six patients with bilateral damage to the ventromedial prefrontal cortex (all known to to be poor at real life decision making) and 10 normal controls. They were each given some fake money and asked to choose cards from four piles, A, B, C, and D which told them whether they had won or lost money. Cards from piles A and B gave higher rewards but much larger losses than those from piles C and D so that in the long run repeatedly choosing A or B cards would result in a loss, and C or D a gain. Skin conductance responses (SCRs) were used as a measure of anxiety and the subjects were asked to explain the game after 20 cards and after each subsequent 10 cards up to 100 choices. After experiencing a few losses in piles A or B normal subjects began to show SCRs before choosing cards from those piles but at that stage they could not explain what was happening. By about card 50 they were able to express a feeling that piles A and B were riskier and by card 80 many could explain why they were riskier (conceptual stage). Seven of the 10 normal subjects and three of the six with prefrontal damage reached the conceptual stage but the normal subjects who did not reach that stage nevertheless learned to choose well whereas the brain damaged patients continued to choose badly even after they were able to reason which piles were risky. Situations requiring decisions probably activate neural systems holding subconscious information based on previous emotional responses to similar situations and decisions. Non-conscious signals, partly autonomic, then motivate decision making before conscious reasoning becomes effective. ‘Playing a hunch’ is probably an essential part of human decision making, allowing correct decisions to be made more rapidly than is possible by reasoning.