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 20–89. When we classify those individuals ages 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.

Cortical pattern separation and item-specific memory encoding

“…This may also be why responses here but not in the previous study were also less accurate for lures than for studied and novel items. The pattern observed here is consistent with previous findings of reduced performance for lures (e.g., Stark et al, 2013;Toner et al, 2009), and with claims that lure discrimination places greater demands on pattern separation (Kirwan and Stark, 2007; and/or post-retrieval processing (Brainerd et al, 2003;Morcom, 2015) and is therefore associated with reduced accuracy.…”

“…Faster RTs at study to both repeated and similar items are consistent with priming of similar items based on overlapping perceptual or conceptual features (Stenberg et al, 2009). Performance on the 'same/similar/new' recognition test was similar to that in previous reports (Garoff et al, 2005;Stark et al, 2013;Toner et al, 2009) with participants most often correctly classifying studied, lure and novel images as 'same', 'similar' and 'new', respectively.…”

“…The recognition test employed studied, novel and lure images and participants made 'same', 'similar' or 'new' judgements (Garoff et al, 2005;Koutstaal et al, 1999). This task is thought to place greater demands on pattern separation than dichotomous old/new recognition (Stark et al, 2013), and supports direct comparisons between successful and unsuccessful lure mnemonic discrimination . Finally, we assessed whether the same regions engaged in pattern separation or completion were also associated with item-specific or gist encoding.…”

“…Although pattern separation is by definition an encoding process, and pattern completion a retrieval process, either or both can be elicited by a single event, whether novel or previously encountered (Hunsaker and Kesner, 2013). Efficient pattern separation at encoding is thought to contribute to later mnemonic discrimination between events with similar representations, while false recognition of similar events can result from inefficient pattern separation or dominance of pattern completion at encoding (Sahay et al, 2011;Stark et al, 2013;Wilson et al, 2006). However the precise mechanisms by which pattern separation and completion at encoding contribute to memory outcomes remain unknown, and it remains to be established whether and how neocortex complements the central role of the hippocampus in these computations.…”

Pattern separation performance is decreased in patients with early multiple sclerosis

“…First, patients and healthy controls were tightly matched on age because it has been demonstrated that pattern separation performance is negatively correlated with age (Holden, Toner, Pirogovsky, Kirwan, & Gilbert, 2013;Stark, Yassa, Lacy, & Stark, 2013). Second, patients and controls performed equally in the CSCT, excluding encoding deficit due to impaired attention or slowing of information processing speed.…”