Relationships between cognitive function and frontal grey matter volumes and thickness in middle aged and early...

The study examined the relationship of lateral frontal cortical volume and thickness with cognitive function in two samples of healthy middle aged (MA, 44-48 years old) and early old-age (OA, 64-68 years old) adults. T1-weighted magnetic resonance imaging scans were acquired in 400 MA and 397 OA adults from respective random community samples. Cortical volumes and thickness were measured with a surface-based segmentation procedure (http://surfer.nmr.mgh.harvard.edu). Volumes of lateral frontal grey matter were found to be significantly lower for OA than MA. Structure-function relationships were investigated using path analyses. In OA, smaller lateral frontal volumes were associated with better episodic memory (EM) (p<0.012, B=-0.117), and Symbol-Digit Modalities Test (SDM) (p<0.031, B=-0.118) performance. Smaller frontal cortical thickness was also associated with better EM (p<0.01) and SDM (p<0.01) performance in OA. However, in MA greater cortical thickness was associated with better EM and (p<0.01) and reaction time (RT) (p<0.01). OA cohort showed significant positive correlations between Total Brain Volume and SDM, Digit-Backwards span and RT. Possible explanations and implications of the relationships in the context of cognitive aging in healthy adults, and limitations of cross-sectional research are discussed.