Detecting subtle changes in visuospatial executive function and learning in the amnestic variant of mild cognitive impairment

Abstract

Background and purpose: Amnestic mild cognitive impairment (aMCI) is a putative prodromal stage of Alzheimer's disease (AD) characterized by deficits in episodic verbal memory. Our goal in the present study was to determine whether executive dysfunction may also be detectable in individuals diagnosed with aMCI.

Methods: This study used a hidden maze learning test to characterize component processes of visuospatial executive function and learning in a sample of 62 individuals with aMCI compared with 94 healthy controls.

Results: Relative to controls, individuals with aMCI made more exploratory/learning errors (Cohen's d = .41). Comparison of learning curves revealed that the slope between the first two of five learning trials was four times as steep for controls than for individuals with aMCI (Cohen's d = .64). Individuals with aMCI also made a significantly greater number of rule-break/error monitoring errors across learning trials (Cohen's d = .21).

Conclusions: These results suggest that performance on a task of complex visuospatial executive function is compromised in individuals with aMCI, and likely explained by reductions in initial strategy formulation during early visual learning and "on-line" maintenance of task rules.

Figure 1. The Groton Maze Learning Test: Stimulus and Examples of Error Types.

Tiles shaded in gray represent one of the hidden maze pathways on the GMLT; numbers indicate order of moves for a sample participant; Move 2 to 3 (shown in black): exploratory error; Move 3 to 4 (shown in red): rule-break error (tapping on same tile twice); Move 8 to 9 (shown in green): perseverative error; Move 12 to 13 (shown in grey): rule break error (not moving back to the last correct tile); Move 16 to 17 (shown in blue): rule break error (no moving diagonally); Move 20 to 21 (shown in purple): rule break error (moving backwards along the maze).

Figure 2. Mean Exploratory Errors and Rule Break Errors (with Standard Errors) over five learning trials of the Groton Maze Learning Test in Healthy Controls versus aMCI groups.