Distinct contributions of dissociable brain networks and hippocampal subregions to memory fidelity
Presented During:
Thursday, June 26, 2025: 11:30 AM - 12:45 PM
Brisbane Convention & Exhibition Centre
Room:
P2 (Plaza Level)
Poster No:
838
Submission Type:
Abstract Submission
Authors:
Helena Gellersen1, Xenia Grande2, Emrah Düzel1, David Berron1
Institutions:
1German Center for Neurodegenerative Diseases, Magdeburg, Sachsen-Anhalt, 2Oxford University, Oxford, Oxfordshire
First Author:
Co-Author(s):
Introduction:
A crucial function of memory is to distinguish between similar experiences. Mnemonic discrimination tasks that require participants to tell apart targets and highly similar lures can probe a brain region's ability to resolve interference (Stark et al., 2019). These tasks implicate hippocampal subfields dentate gyrus (DG) and CA3 in pattern separation (PS), a process to orthogonalize similar stimuli to reduce overlap. Cortical regions may also contribute to PS in a category-specific manner with some regions biased towards objects and others for scenes (Berron et al., 2018). To identify category-specific and -invariant neural correlates of mnemonic discrimination we leveraged 7-Tesla imaging. This method could overcome limitations of prior 3T human functional MRI studies which were unable to distinguish signals from the DG and CA3 hippocampal subfields, did not carry out voxel-wise analyses to assess differences in PS signals in the hippocampal long axis, and left out the amygdala despite its involvement in medial temporal lobe (MTL) memory networks.
Methods:
34 younger adults completed an object and scene mnemonic discrimination task in a 7-Tesla MRI scanner with a field of view covering the MTL and parietal cortex (Fig1). A voxel-wise analysis identified clusters with a PS-like response of higher activation to novel lures compared to repeated targets. This pattern would suggest that a region treats a highly similar stimulus as novel. MTL subregions (Brodmann areas 35 & 36; anterolateral & posterior-medial entorhinal cortex: alERC, pmERC; parahippocampal cortex: PHC; subiculum; cornu ammonis 1 & 3: CA1, CA3; DG) were manually segmented and used as masks for a region of interest analysis that extracted betas from subjects' contrast images in native space.
·Figure 1. Memory tasks.
Results:
The voxel-wise analysis showed that across all trials, objects engaged visual ventral areas, perirhinal cortex (BA35+36), and the amygdala relatively more than scene trials. Scenes elicited greater responses in pmERC, subiculum, PHC, and parietal cortex (Fig2a). Precuneus, right BA35, PHC and posterior DG, CA1, and subiculum were more active during correct scene lure mnemonic discrimination compared to repeats. For objects, this was the case for left BA35, right anterior CA3, and bilateral posterior DG and amygdala (Fig2b). When comparing contrast values across entire anatomical regions, there was no significant difference between alERC and pmERC or PRC and PHC activity during correct object and scene discrimination. Analysis of individual trial-type responses showed strong repetition suppression in CA3 reflected by lower activity during repeated targets and lures compared to novel stimuli. CA3 did not consistently distinguish lures from repeats or correct from incorrect lures. Consistent with pattern separation, DG and the amygdala made these distinctions for objects. AlERC did so for objects and scenes. PS-like DG responses were significantly correlated with scene mnemonic discrimination ability (p<.1 for objects; Fig2c). This correlation was not apparent for CA3 or other regions.
·Figure 2. Activity patterns during object and scene memory and their behavioural relevance.
Conclusions:
We replicate prior findings of a posterior-medial network biased towards scene processing and an anterior-temporal network biased towards objects. This distinction was not as apparent during successful mnemonic discrimination. Instead, scene mnemonic discrimination was biased towards the right MTL. Hippocampal PS-signals were largely found in posterior regions. Several other MTL regions also showed strong PS-like responses. Future work should test whether these signals reflect input to or output from the hippocampus. We also found distinct response patterns for DG and CA3 subfields, suggesting that the DG has a greater capacity to resolve feature interference. PS-like activation in DG specifically correlated with better memory performance. These findings provide a more fine-grained map of MTL contributions to object and scene memory and highlight the behavioural relevance of DG signals for memory fidelity.
Learning and Memory:
Long-Term Memory (Episodic and Semantic) 1
Modeling and Analysis Methods:
Activation (eg. BOLD task-fMRI) 2
Keywords:
Cognition
FUNCTIONAL MRI
HIGH FIELD MR
Memory
1|2Indicates the priority used for review
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Provide references using APA citation style.
Stark, S. M., Kirwan, C. B., & Stark, C. E. (2019). Mnemonic similarity task: A tool for assessing hippocampal integrity. Trends in Cognitive Sciences, 23(11), 938-951.