Cortical responses to sustained and divided attention in Alzheimer's disease

Neuropsychological data suggests that divided attention is more impaired than sustained attention during the early phases of Alzheimer's disease. The purpose of the present study was to compare cerebral activation patterns during sustained and divided attention between Alzheimer patients and healthy elderly. The O-15-water PET activation method was used to map sustained and divided attention in 16 patients with Alzheimer's disease (mean age +/- SD: 68 +/- 5 years; MMSE: 11-25, mean +/- SD = 19.5 +/- 4.9) and in 16 healthy age-matched control subjects. After stereotactical normalization, voxel-by-voxel t statistics was used to assess the significance of activated brain areas and to compare activations between patients and control subjects. In the healthy elderly, sustained and divided attention both elicited activation of the right inferior parietal lobule, and the right middle frontal gyrus, whereas the anterior cingulate gyrus was activated during sustained attention only. Only medial frontal structures (Brodmann Area (BA) 32/34) were activated in Alzheimer patients, and both frontal (BA-10), posterior cingulate (BA-23/31), and subcortical sites were deactivated. Compared to the healthy elderly, the activations in the patients of the right medial (BA-11) superior (BA-10) and inferior (BA-47) frontal gyri, the right middle temporal (BA-20), and the left lingual (BA-17) gyri were significantly reduced. More cortical sites differed statistically between Alzheimer patients and control subjects during divided than during sustained attention. The activation pattern elicited by attention supports the neuropsychological data that divided attention is more impaired than sustained attention in early Alzheimer's disease.