Event-related functional magnetic resonance imaging investigation of executive control in very old individuals with mild cognitive impairment

Abstract

Background: Attentional control of executive cognitive function (ECF) decreases in older individuals with Alzheimer Disease (AD). In order to examine early AD-related changes in the neural substrates of ECF attentional control, we measured activation dorsolateral prefrontal (dLPFC), posterior parietal (PPC), and anterior cingulate cortex (ACC) in adults with mild cognitively impairment (MCI) and in cognitively normal (CN) adults.

Methods: Functional magnetic resonance imaging analysis of brain activation in MCI (n = 8, mean age 79.5) and CN (n = 8 mean age 81.5) during increasing loads of attentional demands.

Results: MCI and CN older adults performed with similar accuracy and reaction time. MCI had greater activation than CN in PPC (right p = .03 and left p = .05) and dlPFC areas (right p = .002 and left p = .004), while activation in ACC was similar in the two groups. Response to increasing loads of the task differed by group: MCI selectively engaged bilateral PPC (right p = .03, left p = .04), while CN subjects increased bilateral dlPFC activation (right p = .005 and left p = .02) and ACC activation (p = .04). Among MCI, greater load-related changes in PPC activity were associated with smaller load-related changes in accuracy rates (r = -.85, p = .07) and greater increases in reaction times (r = .97, p = .01). In CN subjects, load-related change in PPC activation was associated with load-related change in reaction time (r = .76, p = .02) but not with changes in accuracy rates.

Conclusions: PPC and dlPFC may show early functional changes associated with MCI.

Figures

Figure 1

One example for each of two conditions is illustrated. ^Indicates button placed underneath the right or left finger.

Figure 2

Group Reaction time (RT) and Accuracy Rate (AR) during POP task in Cognitively Normal (CN) and MCI older adults (n = 8 and n = 6, respectively). Green and red indicate low load and high load condition, respectively. Boxplots indicate interquartile range (box), median (line across the box) and extreme values (whiskers). POP, Preparing to Overcome Prepotency task; MCI, mild cognitive impairment.

Figure 3

Regions of Interest [upper row: (A– B)] included Brodmann area 7 (BA7), Brodmann area 46 (BA46) and Anterior Cingulate Cortex (ACC) as defined from our previous study (Carter et al 2000). Time Series activation (C– E) are illustrated for MCI (n = 8) and cognitively normal older adults (CN, n = 8) during low-load and high-load condition. Brain fMRI signal change was measured in PPC and dlPFC during the preparation phase and in ACC during the decision phase of the task dlPFC, dorsolateral prefrontal cortex; PPC, posterior parietal cortex; ACC, anterior cingulate cortex; fMRI, functional magnetic resonance imaging.

Figure 4

Scatterplots of the association between increase in reaction time [RT] (high load – low load/low load) and increase in average fMRI signal change (high-load –low load) in PPC (right BA7) and dlPFC (right BA46). Gray triangles refer to MCI (n = 6) and black circles indicate cognitively normal (CN) adults (n = 8). Regression lines are shown for cognitively normals (black) and MCI (gray). fMRI, functional magnetic resonance imaging; PPC, posterior parietal cortex; dlPFC, dorsolateral prefrontal cortex; MCI, mild cognitive impairment.