Selective attention in normal elderly, amnestic mild cognitive impairment, and early Alzheimer's disease: Evaluation of psychometric tests of frontal function and saccadic eye movements

Recent evidence has suggested that deficits in selective attention (i.e., focusing on a single relevant stimulus at one time while ignoring distracting stimuli) may contribute to reduced performance in various cognitive domains, including memory and executive function. Apart from an episodic memory deficit in Alzheimer's disease (AD), several researchers have proposed that selective attention is the first to deteriorate, preceding impairments in perceptual and language function, and potentially having a substantial impact on function.; Many theories emphasize the role of inhibition in selective attention. According to these theories, relevant stimuli are targeted for processing, while irrelevant or distracting stimuli are actively disengaged from potential response systems. Therefore, decrements in inhibitory processes may result in ineffective selective attention, and in turn, produce prolonged maintenance of irrelevant information in working memory. While a diminished inhibitory system appears to provide an explanation for memory and selective attention deficits in patients with early AD, selective attention in patients with amnestic Mild Cognitive Impairment (MCI) is unknown. Several investigators have suggested that patients with AD experience MCI before reaching the clinical threshold for the diagnosis of probable AD. While some consider MCI patients to be at risk for the development of AD, a diagnosis of amnestic MCI does not necessarily entail progression to AD. Regardless of a conversion, evaluation of selective attention is crucial in differentiating normal- and abnormal age-related attentional deficits.; Reliable screening tools of frontal function and selective attention may provide valuable clinical information in the diagnosis of amnestic MCI. Psychometric tests such as the Stroop Neuropsychological Inventory Test and the Wisconsin Card Sorting Test are measures of selective attention and frontal function, and have been widely standardized in normal elderly and in patients with AD. Saccadic eye movements (i.e., rapid, redirection of gaze from one location to another), including pro- and anti-saccades, are particularly helpful as there is considerable overlap in brain areas affected in AD and those used to control eye movements. The use of such diagnostic tools to detect the earliest signs of cognitive impairment may provide individuals with future treatment options and in turn, possibly alter the rate of progression to dementia.