Relating Hippocampus to Relational Memory Processing across Domains and Delays

Abstract

The hippocampus has been implicated in a diverse set of cognitive domains and paradigms, including cognitive mapping, long-term memory, and relational memory, at long or short study–test intervals. Despite the diversity of these areas, their association with the hippocampus may rely on an underlying commonality of relational memory processing shared among them. Most studies assess hippocampal memory within just one of these domains, making it difficult to know whether these paradigms all assess a similar underlying cognitive construct tied to the hippocampus. Here we directly tested the commonality among disparate tasks linked to the hippocampus by using PCA on performance from a battery of 12 cognitive tasks that included two traditional, long-delay neuropsychological tests of memory and two laboratory tests of relational memory (one of spatial and one of visual object associations) that imposed only short delays between study and test. Also included were different tests of memory, executive function, and processing speed. Structural MRI scans from a subset of participants were used to quantify the volume of the hippocampus and other subcortical regions. Results revealed that the 12 tasks clustered into four components; critically, the two neuropsychological tasks of long-term verbal memory and the two laboratory tests of relational memory loaded onto one component. Moreover, bilateral hippocampal volume was strongly tied to performance on this component. Taken together, these data emphasize the important contribution the hippocampus makes to relational memory processing across a broad range of tasks that span multiple domains.

Medial temporal lobe viscoelasticity and relational memory performance

“…This result was obtained even though delayed-memory task performance correlated significantly with SR task performance in the current sample (SRd: r = 0.59, p = 0.010*; SRa: r = 0.58, p = 0.012*). We note that in our recent study comparing hippocampal volume in older adults to multiple measures of memory performance (Monti et al, 2015), correlations of hippocampal volume were weaker with delayed recall performance than with SR task performance, suggesting that perhaps these standard neuropsychological tests may be less sensitive to differences in hippocampal integrity than the SR task performance measures used here. Moreover, performance on both delayed-memory tasks exhibited less variation (words: 24.2% and stories: 23.2%) than did the SR (SRd and SRa) performance measures here (28.2% and 46.5%), consistent with the idea that the SR task is more sensitive to functional differences within a normal, homogeneous population than are the more standard neuropsychological measures used here.…”

“…A previous study found that SR performance, and particularly SRa performance, significantly correlated with volume (Monti et al, 2015). However, that work incorporated subjects across a broad age range expected to have substantial variations in volume, whereas in the current population, with a much narrower age range (18–33 yo), we found a very small distribution of bilateral hippocampal volumes (9.27 cm 3 ± 7.7%).…”

“…Successful performance on these tasks also depends on relational memory processes, as they involve binding words or story details to the temporal-spatial context. Recent work has shown that these tasks share considerable variance with the SR task in a principal components analysis (PCA) of performance and regional volumetrics from a population of older adults (Monti et al, 2015), making these tests an appropriate comparator with the SR task here. However, despite the ξ’ measure being strongly correlated with relational memory performance on the SR task, the ξ’ measure was not correlated with delayed-memory performance ( r = 0.14, p = 0.592; Figure 4).…”

“…Relational memory was measured using a computerized Spatial Reconstruction task (Monti et al, 2015; Watson et al, 2013), which is illustrated in Figure 1.B. On each trial, participants studied the locations of five novel line drawings for 20s.…”

“…This advancement affords us the opportunity, for the first time, to investigate the relationship between hippocampal MRE measures and memory function. This is an optimal target for assessing the MRE structure-function relationship given the vast literature linking hippocampal function to relational memory success in both healthy and impaired populations (Cohen and Eichenbaum, 1993; Eichenbaum and Cohen, 2001), as well as the existence of highly sensitive behavioral measures of relational memory processing (Monti et al, 2015). …”