Background: Performance-based tests of daily functioning may improve early dementia screening by reducing reliance on informant- or clinician-rated measures. However, conventional scores often reflect both motor and cognitive impairment, limiting clinical interpretation.

Objective: To identify cortical gray matter volume predictors of average trial time and intra-subject standard deviation (ISD) during a novel performance-based test of daily functioning using ultra-low-field MRI and classification and regression tree (CART) analysis.

Methods: Forty-seven community-dwelling older adults from the MindCrowd cohort (60.66 ± 11.64 years; 72% female) completed a four-trial functional upper-extremity task and underwent ultra-low-field (0.064 T) T1-weighted MRI. Structural images were processed using FreeSurfer. Separate CART models were developed for average trial time and ISD.

Results: CART identified distinct cortical-volume predictors for average trial time and ISD, suggesting that these two performance metrics reflect partially dissociable neural processes.

Conclusions: Average performance and trial-to-trial variability may capture different motor and cognitive contributions to functional task performance. These findings support the potential utility of this novel performance-based test for dementia screening and longitudinal monitoring, although validation in larger diagnostically characterized cohorts is warranted.