A team of scientists studying the human brain at Washington University School of Medicine in St. Louis and the University of Chieti, Italy, report that a simple decision-making task does not involve the frontal lobes, where many of the higher aspects of human cognition, including self-awareness, are thought to originate. Instead, they say, the regions that decide are the same brain regions that receive stimuli relevant to the decision and control the body's response to it. Other researchers had demonstrated the same principle in primates, but many assumed that the more complex human brain would have a more general decision-making module that involved the frontal lobe independently of the neural systems for perception and action.
For the study, volunteers were trained to perform a task that involved discriminating between an image of a face and an image of a building. Varying degrees of noise obscured the image during the brief time it was visible. Volunteers were asked to indicate which type of image they believed they had seen by either moving their eyes in a particular direction if they had seen a face, or pointing their hand in the same direction if they had seen a building. Researchers took functional magnetic resonance imaging scans of subjects' brains as they performed the task. To help distinguish between the influx of sensory information and the decision to move the eye or hand, subjects had to wait for 10 seconds after seeing the image before indicating which type it was.
Scientists concentrated on regions of the brain that are responsible for planning actions (eye or hand movements) in the parietal lobe. Activity in these different regions would increase in correspondence with the type of stimulus a subject was being shown (face or building) and the type of response they were planning as a result (eye or hand movement). When the stimulus had less noise and subjects were more confident in their choice, brain activity levels in the appropriate area rose proportionally.