Dissociation of regional activation in mild AD during visual encoding - A functional MRI study

Objective: The authors studied mild patients with AD with a visual learning paradigm to determine whether activations of medial temporal regions on fM RI differ in AD compared to nondemented individuals. Background: Changes in activation patterns of medial temporal lobe regions may serve as a biologi c marker of altered brain function early in the course of AD. Methods: The authors studied eight healthy young subjects, eight late middle-age nondeme nted volunteers, and seven patients with mild AD. All subjects underwent fM RI scanning in which they viewed a set of geometric designs for 45 seconds. Changes in blood flow were analyzed by comparing the prestimulus fMRI sign al with that present during the stimulus presentation. Results: Patients wi th AD, who had very poor recall of the geometric designs subsequently, show ed increased blood flow (activation) during stimulus presentation only in a visual association area. Both the young and older nondemented subjects, al l of whom had good recall of the designs, showed activations during stimulu s presentation of the right entorhinal cortex, right supramarginal gyrus, r ight prefrontal regions, and left anterior-inferior temporal lobe. The youn ger and older nondemented subjects did not differ in fMRI activation patter ns. Conclusions: Failure of activation in AD of either temporal lobe or pre frontal regions is consistent with established clinical-pathologic correlat ions in AD. fMRI may be useful in confirming a memory disorder diagnosis an d also may be useful in detecting individuals with incipient dysfunction in learning as a result of disorders such as AD.