Neural correlates of memory for object identity and object location: effects of aging

The purpose of this study was to investigate the effects of aging on memory for object identity and object location to determine whether aging affects both posterior neocortical areas that are domain-specific and other brain regions, such as pre-frontal cortex, that are involved in encoding and retrieval regardless of the information that is processed (domain-general). We used positron emission tomography (PET) to measure changes in regional cerebral blood flow (rCBF) in younger and older participants while they were engaged in encoding and retrieving information about object identity and object location. Compared to young adults, older adults showed decreased activation in domain-specific regions of inferior parietal and inferior temporal cortex while engaged in processing (encoding and retrieving) information about object location and object identity, respectively. This decreased specificity in the older adults was accompanied by greater domain-general activation in right prefrontal and premotor cortex during perceptual encoding than during retrieval. Conversely, the younger participants showed greater domain-general activation in right extrastriate cortex (Brodmann area (BA) 18) during retrieval. Moreover, we found that medial temporal and frontal lobes were synergistically activated in younger adults but not in older adults. The pattern of decreased specificity of activation in posterior neocortex with greater activation in anterior neocortex suggests that, with age, compensatory domain-general mechanisms in anterior neocortex are recruited to mitigate altered domain-specific processes. Thus, the results of the present study indicate that the relation between the presumed integrity of various structures, such as the hippocampus, prefrontal cortex, and posterior neocortex, and their pattern of activation, is a complex one that is influenced by age, by the perceptual and cognitive demands of the task and their interaction.