Recruitment of unique neural systems to support visual memory in normal aging

The performance of many cognitive tasks changes in normal aging [1-3]. Rece nt behavioral work has identified some tasks that seem to be performed in a n age-invariant manner [4]. To understand the brain mechanisms responsible for this, we combined psychophysical measurements of visual short-term memo ry with positron emission tomography (PET) in young and old individuals. Pa rticipants judged the differences between two visual stimuli, and the memor y load was manipulated by interposing a delay between the two stimuli. Both age groups performed the task equally well, but the neural systems support ing performance differed between young and old individuals. Although there was some overlap in the brain regions supporting performance (for example, occipital, temporal and inferior prefrontal cortices, and caudate), the fun ctional interconnections between these common regions were much weaker in o ld participants. This suggests that the regions were not operating effectiv ely as a network in old individuals. Old participants recruited unique area s, however, including medial temporal and dorsolateral prefrontal cortices. These unique areas were strongly interactive and their activity was relate d to performance only in old participants. Therefore, these areas may have acted to compensate for reduced interactions between the other brain areas. (C) 1999 Elsevier Science Ltd. All rights reserved.