Attentional deficits in Alzheimer's, Parkinson's, and Huntington's diseases

Attentional deficits have been shown in Alzheimer's disease but it is unknown whether this reflects disease specific impairment or is present in other neurodegenerative disorders.

We administered a verbal dichotic listening task (free recall and selective allocation to the left or right ear) to 17 patients with Alzheimer's disease, 19 patients with Huntington's disease, 10 patients with idiopathic Parkinson's disease with clinical evidence of dementia (DemPD), 22 non-demented patients with Parkinson's disease (PD), and 22 healthy controls. Patients with dementia were matched for dementia severity and performance in the 3 recall conditions was used as a measure of attentional capacity.

Patients with dementia (Alzheimer and Huntington patients, DemPD) were less accurate than those without dementia (PD and normal subjects). Demented subjects performed at comparable levels regardless of specific diagnosis; likewise those without dementia also achieved similar levels. All groups had a right ear preference under the free recall condition. Alzheimer and Huntington patients showed consistent right ear preference under all recall conditions, while PD patients, like controls, could selectively allocate attention to the left under left ear recall, regardless of the presence of dementia.

The findings suggest a double dissociation. Non-selective attentional processing is affected by dementia presence versus absence but not by specific disease, while selective attentional processing shows disease specific impairments, regardless of the presence of dementia.