Decomposing parietal memory reactivation to predict consequences of remembering

Abstract

Memory retrieval can strengthen, but also distort memories. Parietal cortex is a candidate region involved in retrieval-induced memory changes as it reflects retrieval success and represents retrieved content. Here, we conducted an fMRI experiment to test whether different forms of parietal reactivation predict distinct consequences of retrieval. Subjects studied associations between words and pictures of faces, scenes, or objects, and then repeatedly retrieved half of the pictures, reporting the vividness of the retrieved pictures ('retrieval practice'). On the following day, subjects completed a recognition memory test for individual pictures. Critically, the test included lures highly similar to studied pictures. Behaviorally, retrieval practice increased both hit and false alarm rates to similar lures, confirming a causal influence of retrieval on subsequent memory. Using pattern similarity analyses, we measured two different levels of reactivation during retrieval practice: generic 'category-level' reactivation and idiosyncratic 'item-level' reactivation. Vivid remembering during retrieval practice was associated with stronger category-and itemlevel reactivation in parietal cortex. However, these measures differentially predicted subsequent recognition memory performance: whereas higher category-level reactivation tended to predict false alarms to lures, item-level reactivation predicted correct rejections. These findings indicate that parietal reactivation can be decomposed to tease apart distinct consequences of memory retrieval.

Neural reactivation in parietal cortex enhances memory for episodically linked information

“…As such, it is possible that activation of event representations-supported by the parietal subnetwork (38)-should facilitate semantic or conceptual associations between contextually linked items, but at the cost of sensory detail. This prediction aligns with recent neuroimaging findings from Lee et al (39).…”

“…For example, van der Linder et al (19) found that increased angular gyrus activity accompanied memory benefits during schematic encoding. Recent work also indicates that retrieval-related activity in the parietal subnetwork is associated with increased generalization of episodic memories (39,40).…”

Retrieval aids the creation of a generalised memory trace and strengthens episode-unique information

“…This is consistent with these areas' role in the retrieval of semantic and schema-relevant information (Binder et al, 2009;Binder and Desai, 2011;Linden et al, 2017;Sommer, 2016), with some authors specifically highlighting these regions as hubs responsible for recombining or integrating schema-consistent information (Gilboa & Marlatte, 2017;Himmer et al, 2019;. Categorical reactivation in the same set of areas has previously been observed in a study investigating repeated memory retrieval (Lee et al, 2017), and the location of our semanticisation effects is thus largely consistent with the existing literature.…”

“…In terms of location, both of our searchlights produced effects in the parietal cortex, generally highlighting the role of posterior association cortices in representing reactivated mnemonic content during recall (Lee et al, 2017) and imagery , and reflecting the dynamic change of these mental representations over time (Sommer, 2016). Interestingly, we found distinct sub-regions within the parietal lobe to track the changes on the categorical-semantic and the episodic-contextual level, with very little overlap between the two searchlight analyses (see Supplementary Figure 3).…”

Flexible updating of dynamic knowledge structures

“…Alternatively, posterior areas could start to represent items in a less detailed, more abstracted fashion. Some evidence for this latter suggestion comes from a recent study by Lee, Samide, Richter, and Kuhl 39 . The authors demonstrated that both specific item-level information as well as category level information could be decoded from AnG.…”