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Visuospatial deficits are among the first symptoms of Alzheimer disease (AD) and linked to lower activation in the superior parietal cortex as assessed with functional imaging. Near-infrared spectroscopy (NIRS) is an optical method to measure changes in the concentration of oxygenated hemoglobin and deoxygenated hemoglobin in the microvascular system of the cortex. Because of its advantages in measurement situation, NIRS has proven to be especially suited for investigating psychiatric patients. The aim of this study was to probe the activation of parietal regions in patients with AD, performing a visuospatial task by means of functional NIRS (fNIRS).Thirteen patients with suspected mild AD and 13 healthy subjects comparable in age and gender were investigated while working on a modified version of the Benton Line Orientation Task.During the spatial task, healthy subjects showed explicit parietal activation, whereas patients displayed only activation during the control task. Interestingly, there was no difference in visuospatial performance between the two groups.The results indicate that fNIRS is able to measure parietal activation deficits in patients with AD, which could be developed into an early detection method in the future.