Orienting of visual attention in Alzheimer's disease: its implication in favor of the interhemispheric balance.

Visual attention in dementia of Alzheimer's disease (AD) has not been investigated as extensively as memory or language. The aim of this research was to study the orienting of attention in patients with AD (which temporo-parietal areas are primarily affected) compared with patients with Parkinson-Dementia, Parkinson's disease, and normal controls, using the Posner paradigm. Subjects were instructed to respond by pressing a response key after the appearance of a target at the same location (valid trial) or at the opposite location (invalid trial) indicated by a central cue (arrow). According to the experimental procedure developed by Posner, it has been hypothesized that parietal lobes are involved in "disengagement operation" (when attention has to move from one location to another in the controlateral field). Results showed no differences between AD and the other groups and between left and right hemifield. In conclusion, the authors did not find any sign of difficulty with disengagement, and results are discussed in terms of Kinsbourne's interpretation of a balance between hemispheres.