A review of longitudinal fMRI studies on age-related changes in functional brain activity

Abstract

In the past two decades neuroimaging studies have tried to unveil the neural mechanisms behind age-related changes in cognitive strategies and performance. Structural imaging studies have shown that brain volume changes throughout the complete life-span and functional imaging studies have reported age-related differences in brain activation and connectivity. The aim of this thesis was to provide an overview of studies that report age-related changes in brain activation as measured with functional MRI in a longitudinal design in healthy subjects. We found 16 studies of which 11 reported changes in activity over time. The majority of studies was performed in children. fMRI task used varied between attention, language, memory, working memory and sensory processing tasks. We found increases and decreases in activation in children between 5 and 20 and adults above age 50. A trend of left-hemispheric increases were shown for children around age 8, adults around age 66 and in language studies. Adolescents between ages 10 and 14 seemed to primarily increase activity in regions in the right hemisphere. We conclude that due to the small number of studies, wide variety of fMRI tasks used across studies and the wide age-range of participants, a meta-analysis is not yet feasible and findings should be interpreted with caution. Furthermore, we suggest that changes in brain volume, performance and BOLD characteristics should be controlled for when studying age-related changes in brain activation using the BOLD signal. Also, we stress the importance of including information about the nature of a longitudinal activation change and to make a clear distinction whether longitudinal activation differences refer to changes in BOLD signal between two task conditions or between task and rest activation.