Associative recognition in mild cognitive impairment: relationship to hippocampal volume and apolipoprotein E.

Associative memory involves remembering relations between items of information and is critically dependent on the hippocampus, a brain structure that shows early changes in amnestic mild cognitive impairment (aMCI) and Alzheimer's disease. We examined associative and item memory in aMCI with a focus on the role of medial-temporal lobe regions and genetic risk for Alzheimer's disease. Twenty-four individuals with aMCI and 21 demographically matched healthy older adults underwent associative recognition testing, structural brain imaging, and apolipoprotein E (ApoE) genotyping. A significant interaction between group and recognition type indicated poorer associative recognition than item recognition across tasks in the aMCI group relative to controls. Within the aMCI group, associative but not item recognition showed sizable and significant correlations with hippocampal volume (but not with other medial temporal-lobe structures) and with number of ApoE ε4 alleles. Correlations were smaller and generally not significant in the control group. Our findings replicate and extend previous studies by showing an associative recognition impairment in aMCI that is not accounted for by an item recognition deficit, is related to structural integrity of the hippocampus, and increases with genetic risk for Alzheimer's disease.