A high-resolution single photon emission computed tomography study of verbal recognition memory in Alzheimer's disease

Background: In view of the recent technological advances and its ease of availability, we used single photon emission computed tomography (SPECT) to examine the performance of early Alzheimer's disease (AD) subjects on a verbal recognition memory task. Methods: Eighteen early AD and 10 matched healthy control subjects underwent split-dose ^99mTc-HMPAO (Ceretec®) SPECT using a verbal recognition memory and control task. SPECT images co-registered with MRI scans were used to determine relative regional cerebral blood flow (rCBF) changes in regions of interest. Results: In healthy control subjects, verbal recognition increased rCBF in the right occipital region, thalamus, left prefrontal pole, posterior parietal region and cerebellum, and decreased rCBF in the right hippocampus. AD subjects showed bilateral prefrontal, posterior parietal and occipital increases, unilateral increase in the left posterior temporal region, and bilateral reductions in the hippocampus. Although activation was significantly different between the two groups in the right thalamus and left medial prefrontal region, the verbal recognition task did not enhance discrimination between groups. Conclusions: Compared with controls, AD subjects activate a similar but more extensive bilateral network during verbal recognition, possibly reflecting an attempt to compensate for impaired processing.