Background: Patients with Alzheimer�s disease (AD) often present with apathy symptoms resembling the decreased\nmotivation observed in depressed patients. Therefore, differentiating the initial phase of AD from late life depression\nmay be difficult in some cases. Near-infrared spectroscopy (NIRS) is a functional neuroimaging modality that uses\nnear-infrared light to measure changes in hemoglobin concentration on the cortical surface during activation tasks.\nThe objective of this study was to investigate differences in brain activation associated with late life depression and\nwith AD by means of NIRS.\nMethods: NIRS was performed in 30 patients with depression, 28 patients with AD, and 33 healthy controls, all aged\n60 years or older. During two tasks, a verbal fluency task and a visuospatial task, changes in oxygenated hemoglobin\nconcentration in the frontal and parietal cortices were investigated.\nResults: In the visuospatial task, cortical activation was lower in the depressed group than in the AD group, and\nsignificant differences were observed in the parietal cortex.\nConclusions: NIRS can detect differences in brain activation between patients with late life depression and those\nwith AD. NIRS is a promising tool for the differential diagnosis of late life depression and AD.
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