| Despite the typically progressive nature of dementing diseases, positive behavioral changes such as improved naming performance have been documented when individuals with dementia are provided language treatment (e.g., Dressel et al., 2010). To delineate the underlying neural substrate of such positive changes, researchers have begun to utilize fMRI techniques as a dependent measure for treatment outcomes. fMRI single subject design studies, however, unlike behavioral studies, fail to collect repeated baseline measures and only compare a pre- and post-treatment scan. Given intra-individual variability, practice effects, and the progressive nature of dementing diseases, we hypothesized that individuals with dementia would exhibit different brain activation patterns even without treatment across repeated fMRI sessions.;The purpose of the current study was to evaluate fMRI test-retest reliability among individuals with dementia and neurologically typical older adults using word retrieval tasks to validate the practice of a single pre- versus post-treatment scan comparison. Seven individuals with dementia and 9 age- and education-matched healthy older adults were repeatedly tested over two months using the same fMRI procedures. Five different word retrieval measures were used including object naming, action naming, semantic fluency, letter fluency, and action fluency paradigms to compare reliability across different word retrieval tasks. Our findings suggested that one time fMRI scanning might not adequately represent an individual's typical brain activation patterns to monitor longitudinal changes in dementia. Participants with or without dementia presented different activation patterns at the individual and group levels over time, and the extent of variability varied across individuals, groups, and word retrieval paradigms. Intra-class correlation coefficients demonstrated that some naming paradigms had excellent or good reliabilities whereas others yielded poor reliability. In addition, test-retest reliability varied across different brain regions and groups. These results are consistent with previous studies that reported changes in brain activation with mere repetition of memory tasks in MCI (Belleville et al., 2011) or of language tasks in healthy adults (Gonzalez-Castillo & Talavage, 2011). Given these observed neural fluctuations, one single imaging session might inadequately represent the individual's typical responses and thus multiple imaging baselines are recommended to track longitudinal neural changes. |
