IC-P-007: fMRI activation patterns during encoding and recognition in normal elderly and amnestic mild cognitive impairment patients

Abstract

The clinical hallmark of amnestic mild cognitive impairment (MCI) is memory impairment. Given its obvious functional importance in memory, the medial temporal lobe was targeted with early functional magnetic resonance imaging (fMRI) studies of encoding in MCI. Less is known about the degree to which extra–temporal regions are affected during encoding. Some reports suggest that MCIs may have compensatory increased activation compared to cognitively normal subjects; however, this finding has not been consistently replicated. In addition, relatively little is known about the effects of MCI on recognition memory fMRI response. To examine activation patterns in normal elderly and individuals with amnestic MCI during complex scene encoding and recognition using whole brain fMRI. We studied 18 normal elderly (10/8F; mean 71) and 18 MCIs (10M/8F; mean 76) using block–design paradigms. For the complex scene encoding task, subjects were instructed to memorize pictures. For the recognition task, subjects responded to photographs they recognized from the encoding task. The baseline condition for both tasks required subjects to determine whether two unrecognizable pixelated images matched. The threshold for significance was p <.0001 (uncorrected). During encoding, normal elderly activated three distinct areas bilaterally: parietal–occipital–posterior temporal visual association cortex; medial frontal cortex; and superior/middle/inferior frontal gyri (Figure). During encoding, MCIs activated the same visual association and lateral frontal areas although to a lesser extent; medial frontal activation was absent. During recognition, normals activated the same three areas seen with encoding, although to a lesser extent than during encoding. During recognition, MCIs activated the visual association and lateral frontal areas to a lesser extent than on encoding. In contrast to encoding, a small area of medial frontal activation was present in MCIs. A multi–lobar network was activated during both encoding and recognition tasks in normal elderly. For the most part the same network was activated in MCIs. The extent of activation was generally diminished in MCIs relative to normal elderly, and we did not see clear evidence for compensatory increased activation in MCIs. Furthermore, extent of activation was generally greater during encoding than recognition in both clinical groups.