BRAIN-REGIONS RESPONSIVE TO NOVELTY IN THE ABSENCE OF AWARENESS

Brain regions responsive to novelty, without awareness, were mapped in humans by positron emission tomography. Participants performed a simp le reaction-time task in which all stimuli were equally likely but, un known to them, followed a complex sequence. Measures of behavioral per formance indicated that participants learned the sequences even though they were unaware of the existence of any order. Once the participant s were trained, a subtle and unperceived change in the nature of the s equence resulted in increased blood flow in a network comprising the l eft premotor area, left anterior cingulate, and right ventral striatum . Blood flow decreases were observed in the right dorsolateral prefron tal and parietal areas. The time course of these changes suggests that the ventral striatum is responsive to novel information, and the righ t prefrontal area is associated with the maintenance of contextual inf ormation, and both processes can occur without awareness.