Age-related differences in neural activity during item and temporal-order memory retrieval: A positron emission tomography study

Positron emission tomography (PET) was used to investigate the hypothesis t hat older adults' difficulties with temporal-order memory are related to de ficits in frontal function. Young (mean 24.7 years) and old (mean 68.6 year s) participants studied a list of words, and were then scanned while retrie ving information about what words were in the list (item retrieval) or when they occurred within the list (temporal-order retrieval). There were three main results. First, whereas the younger adults engaged right prefrontal r egions more during temporal-order retrieval than during item retrieval, the older adults did not. This result is consistent with the hypothesis that c ontext memory deficits in older adults are due to frontal dysfunction. Seco nd, ventromedial temporal activity during item memory was relatively unaffe cted by aging. This finding concurs with evidence that item memory is relat ively preserved in old adults and with the notion that medial temporal regi ons are involved in automatic retrieval operations. Finally, replicating th e result of a previous study (Cabeza, R., Grady, C. L., Nyberg, L., McIntos h, A. R., Tulving, E., Kapur, S., Jennings, J. M., Houle, S., & Craik, F. I . M., 1997), the old adults showed weaker activations than the young adults in the right prefrontal cortex but stronger activations in the left prefro ntal cortex. The age-related increase in left prefrontal activity may be in terpreted as compensatory. Taken together, the results suggest that age-rel ated changes in brain activity are rather process- and region-specific, and that they involve increases as well as decreases in neural activity.