Decoding the content of recollection within the core recollection network and beyond

Abstract

Recollection – retrieval of qualitative information about a past event – is associated with enhanced neural activity in a consistent set of neural regions (the ‘core recollection network’) seemingly regardless of the nature of the recollected content. Here, we employed multi-voxel pattern analysis (MVPA) to assess whether retrieval-related fMRI activity in core recollection regions - including the hippocampus, angular gyrus, medial prefrontal cortex, retrosplenial/posterior cingulate cortex, and middle temporal gyrus – contain information about studied content and thus demonstrate retrieval-related ‘reinstatement’ (‘reactivation’) effects. During study, participants viewed objects and concrete words that were subjected to different encoding tasks. Test items included studied words, the names of studied objects, or unstudied words. Participants judged whether the items were recollected, familiar, or new by making ‘remember’, ‘know’, and ‘new’ responses, respectively. The study history of remembered test items could be reliably decoded using MVPA in most regions, as well as from the dorsolateral prefrontal cortex, a region where univariate recollection effects could not be detected. The findings add to evidence that members of the core recollection network, as well as at least one neural region where mean signal is insensitive to recollection success, carry information about recollected content. Importantly, the study history of recognized items endorsed with a ‘know’ response could be decoded with equal accuracy. The results thus demonstrate a striking dissociation between mean signal and multi-voxel indices of recollection. Moreover, they converge with prior findings in suggesting that, as it is operationalized by MVPA classification, reinstatement is not uniquely a signature of recollection.

Recollection and prior knowledge recruit the left angular gyrus during recognition

“…For example, recollection-responses in the left AG are heightened for trials with longer relative to shorter presentation at encoding (Vilberg & Rugg, 2009a, 2009b, a trend that we replicated ( Figure 3E). Similarly, this region has been reported to track stimulus repetition (Gilmore et al, 2015;Guerin & Miller, 2011;Nelson, Arnold, Gilmore, & McDermott, 2013), amount of source information at retrieval (Hutchinson et al, 2014), degree of cortical reinstatement from encoding (Jonker, Dimsdale-Zucker, Ritchey, Clarke & Ranganath, 2018;Kuhl & Chun, 2014;Leiker & Johnson, 2014;Thakral et al, 2017b), and subjective memory strength (Rissman et al, 2016;Thakral et al, 2015). This recent evidence is broadly consistent with the mnemonic accumulator hypothesis (Wagner et al, 2005), which states that activity in the posterior parietal cortex tracks the amount of available evidence for an old response during recognition.…”

The posterior parietal cortex and subjectively perceived confidence during memory retrieval

“…This indicates that recollection itself relies on other brain regions, such as the hippocampal formation, that are more involved in binding episodic representations, which influence the richness of retrieved memories (Eichenbaum 2001;Bergmann et al 2012;St-Laurent et al 2014. The hippocampal formation and the AG are both part of a complex neural network associated with memory (Hayama et al 2012;Thakral et al 2017b). A close interaction within this memory network could perhaps explain the increased activation in the left AG during recollection (Skinner and Fernandes 2007;Vilberg and Rugg 2008), even though the left AG might not be directly involved in recollection-related processes.…”

Characterizing the role of the hippocampus during episodic simulation and encoding

“…This was computed using a Monte Carlo simulation with 10,000 iterations with an estimated spatial autocorrelation of 11.13 mm (Slotnick, ; Slotnick, Moo, Segal, & Hart, ). Given our a priori interest in the hippocampus, results are reported within an anatomically defined hippocampal mask created by manually tracing the hippocampus in both hemispheres using the across‐participant mean anatomic image based on standard anatomical landmarks (Frisoni et al, ; for similar approaches, see Thakral, Yu, & Rugg, ; Thakral, Wang, & Rugg, ; see Supporting Information Material for a list of whole‐brain subsequent memory results). In addition to the GLM analysis, we also conducted an analysis employing a finite‐impulse response (FIR) model to estimate the timecourses associated with each of the events described above (see Thakral et al, ; Vilberg & Rugg, ).…”