Regional cerebral blood flow and recognition memory in elderly normals: potential application to Alzheimer's disease

Regional cerebral blood flow, a physiological measure of brain function, has been used for the assessment of cognitive dysfunction in Alzheimer's disease. A number of studies have found diminished temporo-parietal regional cerebral blood flow (RCBF) in Alzheimer's disease patients at rest and have differentiated these patients from normal subjects with a high degree of sensitivity. However the majority of the Alzheimer's disease patients have been in the moderate to severe stages of the disorder. Few studies have assessed RCBF in the early stages of Alzheimer's disease. With increasing emphasis now being placed on the early detection of such patients we chose to examine RCBF during a task which made demands on those cognitive processes which are impaired in the early stages of the disease, viz. a recognition--memory task. Using a 32-channel RCBF system, we examined 20 normal control subjects over the age of 60 years and 10 patients with early to moderate Alzheimer's disease. RCBF was examined during a task of recognition--memory, and also at rest. Normal subjects showed a global increase in RCBF, with marked left frontal activation, as compared with when at rest. Resting perfusion was decreased in the Alzheimer's subject, and there appeared to be a greater degree of intersubject variability in flow during activation.