Discriminant validity and neuroanatomical correlates of rule monitoring in frontotemporal dementia and Alzheimer's disease

Despite the predominant frontal neuropathology of frontotemporal dementia (FTD), traditional measures of executive functioning do not reliably distinguish FTD from Alzheimer's disease (AD). Performance monitoring is an executive function that is associated with frontal lobe integrity and may be disrupted in FTD. The current study adopted a component process approach to evaluate the discriminant validity and neuroanatomical correlates of performance monitoring (i.e., rule monitoring) during an executive spatial planning task. Forty-four participants with FTD, 30 with AD, and 27 healthy comparison (HC) subjects completed the Delis-Kaplan Executive Function System (D-KEFS) Tower task. A subset of patients underwent structural magnetic resonance imaging to obtain regional measures of cortical volumes. FTD and AD groups demonstrated significantly poorer overall achievement scores on the Tower test relative to the HC sample, but did not differ from one another. In contrast, the FTD group committed significantly more rule violation errors than both HC and AD groups, indicating poorer performance monitoring. In addition, poorer overall achievement correlated with smaller brain volumes in several regions, including bilateral frontal and parietal regions, whereas an increased number of rule violations correlated specifically with decreased bilateral frontal volume. Both left and right frontal volumes remained significant predictors of rule violation errors after controlling for the contribution of overall achievement on the task and all other brain regions. Findings are consistent with literature implicating the frontal lobes in performance monitoring and highlight the importance of characterizing the component processes of performance failures in the cognitive assessment of FTD and AD.