Compensatory recruitment of neural resources during overt rehearsal of word lists in Alzheimer's disease.

Functional neuroanatomical correlates subserving maintenance rehearsal relative to a reading control task were investigated with positron emission tomography imaging of cerebral blood flow in 6 healthy older participants and 6 patients with mild Alzheimer's disease (AD). Rehearsal and reading rates and number of unique words rehearsed did not differ significantly for the 2 groups. The right dorsolateral prefrontal cortex was activated in both groups during rehearsal, highlighting this region's role in short-term maintenance of verbal information. A shift in cortical processing resources to more anterior brain regions with increased rehearsal list length was seen, likely reflecting greater demands on frontal cortex as cognitive load grows. Whereas controls showed unilateral right frontal activation during rehearsal, AD patients demonstrated bilateral frontal activation, possibly reflecting compensatory recruitment of neural resources.