Adult development and neuropsychological characteristics of temporal order and item memory

Research with neurologically impaired patients suggests that temporal order memory (TOM) and item memory (IM) are associated with the frontal lobes and medial-temporal lobes, respectively. Issues concerning the aging of TOM and IM still remain. First, the frontal lobes may show greater age-related decline than posterior portions of the brain and/or the right hemisphere may show greater decline than the left. Second, TOM and IM may or may not be independent, because findings of double dissociations have not been replicated. Third, the relationship between TOM for items in primary vs. secondary memory is unknown. Finally, the mechanisms controlling TOM are poorly understood, partly because many TOM tests maximize working memory demands, thus masking the roles of strategy, sequencing and inhibition. Thirty-two college-age and 32 older participants completed four sets of TOM and IM tests, each of which measured left- or right-hemisphere function (words vs. faces) and maximized or minimized working memory demands. Participants also completed neuropsychological tests of frontal-lobe function. Composite measures of frontal-lobe and medial-temporal-lobe status based on the age-independent performance on additional neuropsychological tests were used to categorize participants as above or below the mean. These composites were used to predict TOM and IM performance, thus measuring their independence. Results showed greater age-related declines in TOM than IM, regardless of whether faces or words were studied, supporting the frontal-lobe hypothesis of aging. The right-hemisphere hypothesis of aging was not supported. IM and TOM were not found to be independent on any of the four sets of tests. However, frontal-lobe status but not medial-temporal-lobe status predicted TOM performance when one or more test item was in primary memory. Frontal-lobe status did not predict IM performance, regardless of whether items were in primary or secondary memory, suggesting that the frontal-lobes may be specifically involved in TOM when information must be held in mind. Correlations between TOM and neuropsychological tests yielded limited support for the theory that cognitive sequencing is involved in TOM.