Aging and prefrontal functions: dissociating orbitofrontal and dorsolateral abilities

This study aimed to determine whether age differentially affects performance on tasks tapping orbitofrontal cortex (OFC) and dorsolateral prefrontal cortex (DLPFC). We administered prefrontal measures to healthy younger (n=23; age=28.4±5.9, education=15.7±2.6, MMSE=29.5±0.6) and older participants (n=20; age=69.1±5.0, education=15.5±3.4, MMSE=28.9±1.5). Groups did not differ on education or mental status, P>0.05. Tasks thought to involve greater OFC processing included the Iowa Gambling Task and Delayed Match and Non-Match to Sample Tasks. Tasks requiring greater DLPFC processing included Petrides’ Self-Ordered Pointing, WAIS-R Digit Span Backward, Letter Fluency, and Months Backward from the Boston Revision of WMS—Mental Control. Composite z-scores were calculated for OFC and DLPFC tasks. A 2×2 ANOVA revealed a Group×Task interaction: F(1,41)=5.55, P=0.02, and a Group main effect: F(1,41)=12.16, P=0.001. Follow-up analyses revealed younger adults outperformed older adults on OFC tasks only (younger=0.37±0.46, older=−0.43±0.70; t(41)=4.5, P<0.001). Post-hoc analyses of individual tasks confirmed that despite age differences on Petrides’ Self-Ordered Pointing, measures requiring relatively greater OFC involvement showed larger effect sizes for age differences. Thus, tasks emphasizing OFC functions appear more sensitive to age effects when directly compared to measures of DLPFC functioning. Reasons for this difference in magnitude may stem from differential aging of prefrontal cortex or differential recruitment of alternative brain regions for successful task completion.