Pattern separation and pattern completion in Alzheimer's disease: Evidence of rapid forgetting in amnestic mild cognitive impairment
Article first published online: 14 AUG 2013
Copyright © 2013 Wiley Periodicals, Inc.
Volume 23, Issue 12, pages 1246–1258, December 2013
How to Cite
Ally, B. A., Hussey, E. P., Ko, P. C. and Molitor, R. J. (2013), Pattern separation and pattern completion in Alzheimer's disease: Evidence of rapid forgetting in amnestic mild cognitive impairment. Hippocampus, 23: 1246–1258. doi: 10.1002/hipo.22162
- Issue published online: 20 NOV 2013
- Article first published online: 14 AUG 2013
- Accepted manuscript online: 27 JUN 2013 03:18AM EST
- Manuscript Accepted: 31 MAY 2013
- NIH. Grant Numbers: AG031925, AG038471
- recognition memory;
Over the past four decades, the characterization of memory loss associated with Alzheimer's disease (AD) has been extensively debated. Recent iterations have focused on disordered encoding versus rapid forgetting. To address this issue, we used a behavioral pattern separation task to assess the ability of the hippocampus to create and maintain distinct and orthogonalized visual memory representations in patients with amnestic mild cognitive impairment (aMCI) and mild AD. We specifically used a lag-based continuous recognition paradigm to determine whether patients with aMCI and mild AD fail to encode visual memory representations or whether these patients properly encode representations that are rapidly forgotten. Consistent with the rapid forgetting hypothesis of AD, we found that patients with aMCI demonstrated decreasing pattern separation rates as the lag of interfering objects increased. In contrast, patients with AD demonstrated consistently poor pattern separation rates across three increasingly longer lags. We propose a continuum that reflects underlying hippocampal neuropathology whereby patients with aMCI are able to properly encode information into memory but rapidly lose these memory representations, and patients with AD, who have extensive hippocampal and parahippocampal damage, cannot properly encode information in distinct, orthogonal representations. Our results also revealed that whereas patients with aMCI demonstrated similar behavioral pattern completion rates to healthy older adults, patients with AD showed lower pattern completion rates when we corrected for response bias. Finally, these behavioral pattern separation and pattern completion results are discussed in terms of the dual process model of recognition memory. © 2013 Wiley Periodicals, Inc.