Cerebral blood flow and BOLD responses to a memory encoding task: A comparison between healthy young and elderly adults

Abstract

Functional magnetic resonance imaging (fMRI) studies of the medial temporal lobe have primarily made use of the blood oxygenation level dependent (BOLD) response to neural activity. The interpretation of the BOLD signal as a measure of medial temporal lobe function can be complicated, however, by changes in the cerebrovascular system that can occur with both normal aging and age-related diseases, such as Alzheimer's disease. Quantitative measures of the functional cerebral blood flow (CBF) response offer a useful complement to BOLD measures and have been shown to aid in the interpretation of fMRI studies. Despite these potential advantages, the application of ASL to fMRI studies of cognitive tasks and at-risk populations has been limited. In this study, we demonstrate the application of ASL fMRI to obtain measures of the CBF and BOLD responses to the encoding of natural scenes in healthy young (mean 25 years) and elderly (mean 74 years) adults. The percent CBF increase in the medial temporal lobe was significantly higher in the older adults, whereas the CBF levels during baseline and task conditions and during a separate resting-state scan were significantly lower in the older group. The older adults also showed slightly higher values for the BOLD response amplitude and the absolute change in CBF, but the age group differences were not significant. The percent CBF and BOLD responses are consistent with an age-related increase in the cerebral metabolic rate of oxygen metabolism (CMRO(2)) response to memory encoding.

Differential age effects on cerebral blood flow and BOLD response to encoding: Associations with cognition and stroke risk

“…However, it should be noted that greater percent change CBF during novel relative to familiar image presentation could reflect a lower level of absolute CBF response during the familiar image condition. As our recent work (Restom et al, 2007) suggests, the greater percent change CBF response during novel picture encoding in the older participants may reflect a lower level of CBF response during the familiar image condition, which would be consistent with the observed age-related reduction in resting-state CBF.…”

“…Thus, ASL has important implications for diagnosis, treatment monitoring, and outcome prediction in dementia, stroke, and other neurological diseases (Warach et al, 1996). Initial studies assessing both BOLD and CBF in the MTL during encoding have demonstrated the feasibility of this technique in older adults (Restom et al, 2007). The main challenge is the relatively low contrast-to-noise ratio of the CBF measures.…”

“…Combining both techniques (e.g., FMRI using ASL/BOLD) would provide valuable complements to more fully characterize the neurovascular underpinnings of encoding but would also require the acquisition and joint analysis of quantitative measurement of functional CBF and BOLD responses. Preliminary studies demonstrate the feasibility of using combined ASL/BOLD to measure the functional perfusion and BOLD response to encoding (Restom et al, 2006;Restom et al, 2007).…”

Healthy aging attenuates task-related specialization in the human medial temporal lobe

“…Increasing age is associated with changes in CBF (Biagi et al, 2007;Parkes et al, 2004), which have been shown to influence BOLD fMRI results (Restom et al, 2007). In particular, age-related increases in the BOLD signal may be partly explained by regional reductions in CBF.…”

“…While differences in the experimental design, types of stimuli, and contrasts of interest might explain, to some extent, the discrepant results across studies, biological and technical factors also need to be taken into account, such as age-related changes in cerebral blood flow (CBF; Biagi et al, 2007;Parkes et al, 2004;Restom et al, 2007). Furthermore, the complex anatomy of regions such as the MTL has been shown to be poorly registered to a brain template using standard spatial normalization procedures (Kirwan et al, 2006;Salmond et al, 2002).…”