Reminders reinstate context-specificity to generalized remote memories in rats: relation to activity in the hippocampus and aCC

Abstract

Conditioned fear memories that are context-specific shortly after conditioning generalize over time. We exposed rats to a context reminder 30 d after conditioning, which served to reinstate context-specificity, and investigated how this reminder alters retrieval-induced activity in the hippocampus and anterior cingulate cortex (aCC) relative to a no reminder condition. c-Fos expression in dorsal CA1 was observed following retrieval in the original context, but not in a novel context, whether or not the memory was reactivated, suggesting that dCA1 retains the context-specific representation. c-Fos was highly expressed in aCC following remote memory testing in both contexts, regardless of reminder condition, indicating that aCC develops generalized representations that are insensitive to memory reactivation.

Systems consolidation, transformation and reorganization: Multiple Trace Theory, Trace Transformation Theory and their Competitors

“…Also using MEG, Hebscher et al (2020) observed that inhibiting the precuneus with TMS led to slowed frontally-distributed activity early during the construction phase of autobiographical retrieval, consistent with disruption of frontally-mediated access to personal memories. These findings are also consistent with observations by Sekeres et al (2020) in their reminder experiment (see above), though the temporal precision was much lower in that study.…”

“…The close correspondence between rodent and human studies on systems consolidation is illustrated nicely by Sekeres et al (2018bSekeres et al ( , 2020 who conducted homologous, functional neuroimaging studies on humans and IEG studies on rodents (see above). Using fMRI during encoding and retrieval of memories of the video clips from St-Laurent et al ( 2009), Sekeres et al (2018b) tracked memory transformation and its neural correlates over time in neurologicallyintact people.…”

“…For example, manipulating gist vs. detailed retrieval orientation influences the quality of subsequently retrieved autobiographical memories (Rudoy et al 2009) and can offset age-related deficits in retrieval of episodic details (Aizpurua & Koutsaal, 2016). Similarly, provision of reminders can revive detail retrieval, as is the case for hippocampally mediated context specific memory at remote time-points in both humans (Sekeres et al, 2020) and rodents (Winocur et al, 2007; see review in Jasnow et al, 2017). Reminders can reactivate dormant or silent, presumably, hippocampal engrams via the mPFC, and change performance from being dependent on context-general memories to context-specific ones, a process, we noted, can be mimicked by direct optogenetic activation of silent hippocampal engrams (Guskjolen et al, 2019).…”

No consolidation without representation: Correspondence between neural and psychological representations in recent and remote memory

“…In previous reviews, we have noted a strong correspondence between human studies on memory consolidation and transformation and rodent studies conducted at the same level of analyses (Winocur et al, 2010;Dudai, 2012;Kandel et al, 2014;Sekeres et al, 2018aSekeres et al, , 2018bSekeres et al, , 2019. Here, we briefly review such findings in light of the different types of representations: detailed versus gist event-specific memory (Figure 1A), schematic event-general knowledge (Figure 1B), and what might be considered an animal analog to human abstract (semantic) knowledge (Figure 1C).…”

Schemas provide a scaffold for neocortical integration at the cost of memory specificity over time

“…Sekeres et al , 2018). Should task demands tax the memory system to retrieve such detail, we predict the hippocampus would be required – as demonstrated in rodent (and human) studies of memory in the absence of a learned schema (Winocur, Moscovitch and Bontempi, 2010; Sekeres et al , 2018, 2020; Sekeres, Winocur and Moscovitch, 2018).…”