A task to assess behavioral pattern separation (BPS) in humans: Data from healthy aging and mild cognitive impairment

Abstract

Changes in memory performance are one of the hallmark symptoms of mild cognitive impairment and are affected by healthy aging as well. Pattern separation, which refers to the process of orthogonalizing overlapping inputs into distinct memory representations, may be a sensitive marker of these memory changes. Here, we describe a paradigm, the Behavioral Pattern Separation Task-Object Version (BPS-O task), which reveals age-related changes in pattern separation performance. Specifically, we report an age-related decline in pattern separation in healthy adults, ranging from ages 20 to 89. When we classify those individuals aged 60 and older into two groups, Aged Unimpaired (AU) and Aged Impaired (AI) based on their delayed word recall performance, we observe impairments in pattern separation performance in the Impaired group, but no overall impairment in recognition performance. In contrast, those individuals diagnosed with mild cognitive impairment demonstrate worse performance than age-matched controls in both pattern separation and recognition memory performance. Therefore, the BPS-O task provides a sensitive measure for observing changes in memory performance across the lifespan and may be useful for the early detection of memory impairments that may provide an early signal of later development to mild cognitive impairment.

Keywords: Dentate gyrus (DG); Healthy aging; MCI; Pattern separation.

Copyright © 2013 Elsevier Ltd. All rights reserved.

Figures

Figure 1

Participants encoded a series of pictures, followed by a surprise recognition test, which contained exact repetitions (identical to those in the encoding task), novel foils (completely new items), and similar lures (related, but not identical, to those in the encoding task).

Figure 2

There is no effect of age on recognition performance (old responses to true repetitions – old responses to foils) (2A). In contrast, there is a linear decrease across age groups for pattern separation performance (similar responses to lures – similar responses to foils) (2B). This linear decrease can also be characterized by a negative correlation between pattern separation score and age (2C). For older individuals (ages 60–89), there is a positive relationship between pattern separation performance and delayed word recall on the RAVLT (2D).

Figure 3

We split the healthy older individuals into two groups: the aged unimpaired group has RAVLT scores of 12–15 and the impaired group has scores of 5–8. While there is no difference in recognition performance between the two healthy aged groups, the MCI group has a significant decrease in recognition memory (3A). In contrast, pattern separation performance is impaired for both the aged impaired and MCI groups compared to the unimpaired group (3B). Ranking the lure bins by degree of similarity (L1 – most similarity; L5 – least similarity) revealed a main effect of age group (3C) and a group effect for the unimpaired, impaired, and MCI groups (3D).