Functional neural correlates of attentional deficits in amnestic mild cognitive impairment

Abstract

Although amnestic mild cognitive impairment (aMCI; often considered a prodromal phase of Alzheimer's disease, AD) is most recognized by its implications for decline in memory function, research suggests that deficits in attention are present early in aMCI and may be predictive of progression to AD. The present study used functional magnetic resonance imaging to examine differences in the brain during the attention network test between 8 individuals with aMCI and 8 neurologically healthy, demographically matched controls. While there were no significant behavioral differences between groups for the alerting and orienting functions, patients with aMCI showed more activity in neural regions typically associated with the networks subserving these functions (e.g., temporoparietal junction and posterior parietal regions, respectively). More importantly, there were both behavioral (i.e., greater conflict effect) and corresponding neural deficits in executive control (e.g., less activation in the prefrontal and anterior cingulate cortices). Although based on a small number of patients, our findings suggest that deficits of attention, especially the executive control of attention, may significantly contribute to the behavioral and cognitive deficits of aMCI.

Figure 1. Schematic of modified Attention Network Test for geriatric samples (ANT-G).

In each trial, depending on the cue condition (no cue, double cue, spatial cue), a box changes from black to white (flashes) for 100 ms. After 400 ms, the target (center arrow) and four flanker arrows (two on either side of center arrow, congruent or incongruent with center arrow) are presented for 2500 ms. The participant makes a response to indicate the direction of the center arrow (left or right). The response window remains open for an additional 1500 ms after the termination of the target (4000 ms in total for the response window), proceeding into the 2500 ms inter-trial interval.

Figure 2. Group differences in median reaction time by attentional function.

Only the group difference for the flanker conflict (executive control) effect reached significance at p<0.05 (actual p<0.01). Error bars represent standard error.

Figure 3. Cortical surface maps of Alerting and Orienting effects for aMCI>HC contrast.

All represented activity has been thresholded at p<0.05 for height and k = 120 (p<0.05) for cluster extent to set the nominal alpha level to p<0.05 for multiple comparisons (corresponds to t t ≥1.76), based on Monte Carlo simulation of our data.

Figure 4. Cortical surface maps of Executive Control effect for HC, aMCI, and group contrast (HC>aMCI).

The top set is the contrast between flanker incongruent and flanker congruent conditions in Healthy Controls (HC). The middle set is the contrast between flanker incongruent and flanker congruent conditions in patients with amnestic Mild Cognitive Impairment (aMCI). The bottom set is the contrast between HC and aMCI. All represented activity has been thresholded at p<0.05 for height and k = 120 (p<0.05) for cluster extent to set the nominal alpha level to p<0.05 for multiple comparisons, based on Monte Carlo simulation of the data.