Neural correlates of focused attention in cognitively normal older adults, patients with mild cognitive impairment and patients with mild Alzheimer's disease
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Impaired attention can hinder information processing at multiple levels and may explain some aspects of the cognitive decline in aging. An inefficient inhibitory system can lead to deficits in focused attention (FA). FA deficits are observed in patients with mild cognitive impairment and Alzheimer’s disease (AD). The Stroop task was applied to functional magnetic resonance imaging (fMRI) to investigate the neural correlates of FA in cognitively normal older adults (NC), patients with amnestic MCI (aMCI) and patients with mild AD. Twenty-one NC, seven aMCI and fifteen mild AD patients performed a verbal Stroop- fMRI paradigm. Both structural and T2*-weighted functional scans were acquired. In Series 0, subjects were presented with colour words printed in black ink and were asked to read the word. In Series 1 and 2, subjects were presented with colour words printed in an incongruent ink colour. Series 1 had four blocks of the ‘Read the word’ condition followed by four blocks of the ‘Say the colour of the ink’ condition. Series 2 had eight blocks of alternating ‘Read the word’ and ‘Say the colour of the ink’ conditions. SPM5 was used to detect anatomical areas with significant signal intensity differences between the two conditions. The NC group performed significantly better in the Stroop-fMRI task than the aMCI and mild AD groups. The percentage of errors on incongruent trials was significantly lower in the NC group (2%) than the aMCI (14%) and mild AD (13%) groups. The ‘Say the colour of the ink’ minus ‘Read the word’ contrast for the NC and mild AD groups yielded common areas of activation in the supplementary motor area, precentral gyrus, and inferior frontal gyrus. aMCI patients also showed activation in the precuneus, temporal and postcentral gyri. Worse performance on the Stroop-fMRI task by the aMCI and mild AD groups suggests deficits in FA. This is the first study to investigate the neural correlates of FA using the Stroop task in aMCI and AD patients. The verbal Stroop-fMRI paradigm employed in the current study provides a means to study the neural correlates of FA in older adult and patient populations.