Functional brain imaging of young, nondemented, and demented older adults

Brain imaging based on functional MRI (fMRI) provides a powerful tool for c haracterizing age-related changes in functional anatomy. However, between-p opulation comparisons confront potential differences in measurement propert ies. The present experiment explores the feasibility of conducting fMRI stu dies in nondemented and demented older adults by measuring hemodynamic resp onse properties in an event-related design. A paradigm involving repeated p resentation of sensory-motor response trials was administered to 41 partici pants (14 young adults, 14 nondemented older adults, and 13 demented older adults). For half of the trials a single sensory-motor event was presented in isolation and in the other half in pairs. Hemodynamic response character istics to the isolated events allowed basic response properties (e.g., ampl itude and variance) between subject groups to be contrasted. The paired eve nts further allowed the summation properties of the hemodynamic response to be characterized. Robust and qualitatively similar activation maps were pr oduced for all subject groups. Quantitative results showed that for certain regions, such as in the visual cortex, there were marked reductions in the amplitude of the hemodynamic response in older adults. In other regions, s uch as in the motor cortex, relatively intact response characteristics were observed. These results suggest caution should be exhibited in interpretin g simple main effects in response amplitude between subject groups. However , across all regions examined, the summation of the hemodynamic response ov er trials was highly similar between groups. This latter finding suggests t hat, even if absolute measurement differences do exist between subject grou ps, relative activation change should be preserved. Designs that rely on gr oup interactions between task conditions, parametric manipulations, or grou p interactions between regions should provide valuable data for making infe rences about functional-anatomic changes between different populations.