A Review on the Trajectory of Attentional Mechanisms in Aging and the Alzheimer's Disease Continuum through the Attention Network Test

Abstract

Multiple domains of cognition are known to decline in both normal aging and in the trajectory towards Alzheimer's disease (AD). While declines in episodic memory are most well-known in both normal aging and AD, some of these memory differences might stem from early deteriorations in attention that have consequences for later memory. Further complicating the matter is that attention is a multifaceted construct that might be differentially affected in normal aging and AD. According to cognitive neuroscience models of attention, three types of attention networks exist: alerting, orienting, and executive. Efficiency of these three networks can be captured using the Attention Network Test (ANT). We reviewed the literature investigating differences in attention networks using the ANT as a function of normal aging and the AD trajectory, which included people at risk for AD, preclinical stages of AD, mild cognitive impairment, and those diagnosed with AD. We found that normal aging and the AD trajectory evidenced different patterns of attentional declines. Whereas normal aging was most consistently associated with impairments in alerting, early phases of the AD trajectory were most consistently associated with impairments in executive attention, and later phases of the AD trajectory were mixed. The mixed results with AD are largely attributed to small sample sizes and confounding effects of general slowing. These findings highlight key gaps in the literature linking different phases of AD while also highlighting the usefulness of the ANT to distinguish normal aging from the AD trajectory, especially in the earliest phases of the disease process.

Keywords: Aging; Alerting; Alzheimer’s Disease; Attention Network Test; Executive Function; Mild Cognitive Impairment.

Figure 1

Schematic of Attention Network Test. Panel A illustrates an alerting trial with a neutral arrow (i.e., no flankers). Alerting is calculated by subtracting response times in the double-cue condition from the no-cue condition. Panel B illustrates an orienting trial with a top spatial cue and a neutral arrow. Orienting is calculated by subtracting response times in the single spatial cue condition from the no cue condition. Panel C illustrates an executive trial with incongruent flankers. In the actual paradigm, these different trials are systematically combined so that all combinations of trials are possible. Executive attention is calculated by subtracting response times in the congruent flanker condition (not shown) from the incongruent flanker condition.

Figure 2

Summary of findings for trends in normal aging (left) and the AD trajectory (right). In normal aging, alerting gradually decreases with age, executive attention declines only in very old age, and orienting is stable. In early phases of the AD trajectory (i.e., normal older adults at risk for AD, preclinical AD, and amnestic mild cognitive impairment), executive attention declines above beyond normal age-related declines in attention. In later phases of the AD trajectory (i.e., diagnosed AD), orienting declines at a similar rate as alerting. Because the likelihood of a diagnosis of AD increases with old age, we use the age-related alerting effect as a reference line. AD = Alzheimer’s disease.