Associative Learning, Acquired Equivalence, and Flexible Generalization of Knowledge in Mild Alzheimer Disease

Background: Acquired equivalence is a phenomenon in which prior training to treat 2 stimuli as equivalent increases generalization between them. Previous studies demonstrated that the hippocampal complex might play an important role in acquired equivalence associative learning. In this study, we tested the possibility that acquired equivalence learning is a sensitive marker of mild Alzheimer disease (AD). Methods: In the associative learning test, antecedent stimuli were cartoon faces and consequent Stimuli were different colored cartoon fishes. Each cartoon character had some pet fish and the task was to learn these face-fish associations using feedback provided after each decision. In the transfer phase, knowledge about face-fish pairs had to be generalized to new associations. Results: AD patients exhibited mild impairments in the training phase, whereas they were profoundly impaired on the acquired equivalence test. Associative knowledge could not be transferred to a more flexible retrieval condition. Conclusions: These results suggest that acquired equivalence learning is specifically impaired in early AD, which may indicate the pathology of the hippocampal complex.