Functional magnetic resonance imaging changes in amnestic and nonamnestic mild cognitive impairment during encoding and recognition tasks

Functional magnetic resonance imaging (fMRI) shows changes in multiple regions in amnestic mild cognitive impairment (aMCI). The concept of MCI recently evolved to include nonamnestic syndromes, so little is known about fMRI changes in these individuals. This study investigated activation during visual complex scene encoding and recognition in 29 cognitively normal (CN) elderly, 19 individuals with aMCI, and 12 individuals with nonamnestic MCI (naMCI). During encoding, CN activated an extensive network that included bilateral occipital-parietal-temporal cortex; precuneus; posterior cingulate; thalamus; insula; and medial, anterior, and lateral frontal regions. Amnestic MCI activated an anatomic subset of these regions. Non-amnestic MCI activated an even smaller anatomic subset. During recognition, CN activated the same regions observed during encoding except the precuneus. Both MCI groups again activated a subset of the regions activated by CN. During encoding, CN had greater activation than aMCI and naMCI in bilateral temporoparietal and frontal regions. During recognition, CN had greater activation than aMCI in predominantly temporoparietal regions bilaterally, while CN had greater activation than naMCI in larger areas involving bilateral temporoparietal and frontal regions. The diminished parietal and frontal activation in naMCI may reflect compromised ability to perform nonmemory (i.e., attention/executive, visuospatial function) components of the task.