title: Age-related increases in right frontal activation during task switching are mediated by reaction time and white matter microstructure.
abstract: Age-related increases in right frontal cortex activation are a common finding in the neuroimaging literature. However, neurocognitive factors contributing to right frontal over-recruitment remain poorly understood. Here we investigated the influence of age-related reaction time (RT) slowing and white matter (WM) microstructure reductions as potential explanatory factors for age-related increases in right frontal activation during task switching. Groups of younger (N=32) and older (N=33) participants completed a task switching paradigm while functional magnetic resonance imaging (fMRI) was performed, and rested while diffusion tensor imaging (DTI) was performed. Two right frontal regions of interest (ROIs), the dorsolateral prefrontal cortex (DLPFC) and insula, were selected for further analyses from a common network of regions recruited by both age groups during task switching. Results demonstrated age-related activation increases in both ROIs. In addition, the older adult group showed longer RT and decreased fractional anisotropy in regions of the corpus callosum with direct connections to the fMRI ROIs. Subsequent mediation analyses indicated that age-related increases in right insula activation were mediated by RT slowing and age-related increases in right DLPFC activation were mediated by WM microstructure. Our results suggest that age-related RT slowing and WM microstructure declines contribute to age-related increases in right frontal activation during cognitive task performance.
authors.affiliation: Department of Anatomy and Neurobiology, University of Kentucky, Lexington, KY 40536, USA. Electronic address: zude.zhu@uky.edu.
authors.forename: Z
authors.initials: Z
authors.lastname: Zhu
authors.affiliation: Department of Anatomy and Neurobiology, University of Kentucky, Lexington, KY 40536, USA.
authors.forename: J G
authors.initials: JG
authors.lastname: Hakun
authors.affiliation: Department of Anatomy and Neurobiology, University of Kentucky, Lexington, KY 40536, USA.
authors.forename: N F
authors.initials: NF
authors.lastname: Johnson
authors.affiliation: Department of Anatomy and Neurobiology, University of Kentucky, Lexington, KY 40536, USA; Magnetic Resonance Imaging and Spectroscopy Center, University of Kentucky, Lexington, KY 40536, USA; Sanders-Brown Center on Aging, University of Kentucky, Lexington, KY 40536, USA. Electronic address: brian.gold@uky.edu.
authors.forename: B T
authors.initials: BT
authors.lastname: Gold
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001931:Brain Mapping; D003071:Cognition / Q000502:physiology*; D056324:Diffusion Tensor Imaging; D005260:Female; D005625:Frontal Lobe / Q000166:cytology* / Q000502:physiology*; D007839:Functional Laterality; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011930:Reaction Time / Q000502:physiology*; D066127:White Matter / Q000166:cytology* / Q000502:physiology*
keywords: DTI; aging; mediation; neural efficiency; over-recruitment; task switching