Spatial pattern completion deficits in older adults

Abstract

Aging may have an impact on the CA3 autoassociative network of the hippocampus, posited by computational models as supporting pattern completion. Twenty-five young (YAs) and 25 older adults (OAs) performed a spatial pattern completion task using a computerized navigational paradigm analogous to a rodent pattern completion task reliant on the CA3. Participants identified a previously seen goal location, and the availability of distal cues in the environment was manipulated such that 0, 2, or 4 cues were missing. Performance in both groups declined as a function of decreased cue availability. However, controlling for age differences in task performance during a pre-experimental baseline task, OAs performed equivalently to YAs when all cues were available, but worse than YAs as the number of cues decreased. These findings suggest spatial pattern completion may be impaired in OAs. We discuss these findings in the context of a growing body of literature suggesting age-related imbalances in pattern separation vs. pattern completion.

Keywords: aging; episodic memory; hippocampus; navigation; spatial pattern completion.

Figure 1

Associative memory training task (A and B) and spatial pattern completion (C and D) tasks. (A) In the sample phase of the training task, participants navigated using the arrow keys on keyboard to a green square. (B) During the choice phase, they were required to navigate to the same location the green square was previously presented in, this time in the absence of a visible green square. (C) The sample and (D) choice phases for spatial pattern completion were similar to the training phase, except the number of wall cues available was manipulated such that 0, 2, or all 4 wall cues were missing in the choice phase of spatial pattern completion.

Figure 2

Spatial pattern completion in younger and older adults controlling for baseline associative memory performance. Older adults performed worse overall compared to young adults on a pattern completion task. Older adults performed similarly to young adults when 0 extra-maze cues were missing, but worse when 2 or 4 cues were missing. Error bars show the standard error of the mean.