Age-related changes in cortical blood flow activation during perception and memory.

Although many cognitive functions are affected by age, some are relatively maintained. There also are numerous age-related changes in brain structure, but not much is known about how these changes impact upon the alterations seen in cognition. In order to understand the basis for the reductions and sparings of cognitive function in the aged, experiments were carried out to compare regional cerebral blood flow (rCBF) and performance in young and old subjects on visual perceptual and memory tasks. In the first experiment, which examined the perception of faces and spatial locations, old subjects were as accurate as young subjects, and both groups had rCBF activation in fusiform gyrus during face matching and in superior parietal cortex during location matching. However, old subjects had less activation of prestriate cortex and more activation of frontal and lateral temporal cortex than did young subjects. The second experiment tested recognition memory for faces, a task on which old subjects were impaired. Young subjects had rCBF activation in left prefrontal and inferior temporal cortex and in right hippocampus during encoding of the faces, and in right prefrontal and parietal cortex during recognition. Old subjects showed no significant activation of the areas involved in encoding, but did have increased rCBF in right prefrontal cortex during recognition. These results suggest that the aging brain can demonstrate alterations of the functional systems involved in some cognitive processes, such as perception, that may serve as a compensatory mechanism to maintain performance. Failure to show such compensation, coupled with dysfunction of the areas primarily involved in processing may lead to more marked deficits in performance.