fMRI activation changes during successful episodic memory encoding and recognition in amnestic mild cognitive impairment relative to cognitively healthy older adults.

BACKGROUND/AIMS Previous functional MRI studies in individuals with amnestic mild cognitive impairment (AMCI), a putative, prodromal form of Alzheimer's disease, reveal substantial regional changes in brain activation during episodic memory function. METHODS Functional MRI was applied to examine changes in brain activation during different stages of episodic memory function using a subsequent memory task in individuals with AMCI relative to older normal controls. RESULTS We found that the AMCI group displayed greater activation in the right hippocampus but less activation in the frontal cortex relative to the older normal control group during intentional encoding of items that were subsequently recognized. We observed nearly the opposite pattern of results for successful recognition. The AMCI group displayed less activation in the medial temporal cortex but greater activation in the frontal cortex. In addition, the AMCI group showed reduced activation in the medial temporal and frontal cortices during incidental encoding of novel information during recognition. CONCLUSION The results of the present study suggest that brain activation differences in individuals with AMCI are modulated by the stage of episodic memory examined (i.e. intentional vs. incidental encoding vs. recognition). These observations may help to clarify some of the conflicting findings regarding brain activation changes in AMCI.