Forming Episodic Memories One Transition at a Time

Poster C114 Sketchpad Memory Modulation Lab Department of Psychology & Neuroscience Boston College Forming episodic memories one transition at a time Valentina Krenz & Maureen Ritchey Clewett, D., DuBrow, S., & Davachi, L. (2019). Transcending time in the brain: How event memories are constructed from experience. Trends in Cognitive Sciences, 23(10), 769–783. 1 Ben-Yakov, A., & Dudai, Y. (2011). Constructing realistic engrams: Poststimulus activity of hippocampus and dorsal striatum predicts subsequent episodic memory. Journal of Neuroscience, 31(24), 9032–9042. 3 Cooper, R. A., & Ritchey, M. (2020). Progression from feature-specific activity to hippocampal binding during episodic encoding. Journal of Neuroscience, 40(8), 1701–1709. 4 Cooper, R. A., & Ritchey, M. (2019). Cortico-hippocampal network connections support the multidimensional quality of episodic memory. eLife, 8, e45591. 6 Richter, F. R., Cooper, R. A., Bays, P. M., & Simons, J. S. (2016). Distinct neural mechanisms underlie the success, precision, and vividness of episodic memory. eLife, 5, e18260. 7 Ritchey, M., & Cooper, R. A. (2020). Deconstructing the posterior medial episodic network. Trends in Cognitive Sciences, 24(6), 451–465. 8 5 Baldassano, C., Hasson, U., & Norman, K. A. (2017). Discovering event structure in continuous narrative perception and memory. Neuron, 95(3), 709–721.e5. Barnett, A. J., Nguyen, M., Spargo, J., Yadav, R., Cohn-Sheehy, B. I., & Ranganath, C. (2024). Hippocampal-cortical interactions during event boundaries support retention of complex narrative events. Neuron, 112(2), 319–330.e7. 2 ANALYSIS APPROACH PREDICTED OUTCOME Predicting trial-wise memory outcome based on fMRI patternactivity - L1 regularization - leave-one-out cross validation Do activation patterns at different encoding stages predict item memory and memory specificity? transition points transition points scene offset scene onset scene offset scene onset prediction accuracy item onset item offset 1 0 item memory prediction accuracy item onset item offset 1 0 memory specificity Hypotheses: Activation patterns in content-selective regions and hippocampus predict subsequent memory at item onset and offset, respectively. MPC and LPC predict memory specificity at event offset. item memory: events voxels ROI subject transition point memory specificity: 1 11 1 10 0 0 ANALYSIS APPROACH How do changes in hippocampal–cortical connectivity across an encoding event relate to memory quality? Generalized psychological interaction (gPPI) analysis as the encoding event unfolds PREDICTED OUTCOME transition points transition points scene onset item onset item offset scene offset specific > unspecific scene onset item onset item offset scene offset remembered > forgotten Hypotheses: Connectivity between hippocampus and contentselective regions at item onset is associated with subsequent item retrieval. Hippocampus–parietal cortex (LPC/MPC) connectivity at offset is associated with memory specificity. hippocampus LPC MPC content-selective areas (e.g. LOC) ANALYSIS APPROACH Does LPC/MPC engagement at event offset reflect an early wave of episodic reconstruction? Representational similarity analysis comparing encoding offset and covert retrieval patterns as an indicator of an early memory reconstruction PREDICTED OUTCOME Hypothesis: Greater offset-retrieval similarity in LPC/MPC is associated with memory specificity. ROI subject encoding offset covert retrieval events events voxels voxels same event different event Pearson's r BACKGROUND Offset-related signals have also been observed in regions of the lateral parietal cortex (LPC) and medial parietal cortex (MPC)2,5, though their functional roles during encoding remain unclear. As these regions have been shown to support the vivid and specific reconstruction of episodic experiences during memory retrieval6,7,8, their engagement at encoding event boundaries might reflect an early wave of episodic reconstruction, facilitating memory specificity in the long run. This study investigates the neural dynamics that determine episodic memory quality as an encoding event unfolds, focusing on the hippocampus, parietal cortex, and content-selective regions and their interactions across event transitions. MPC LOC hippocampus LPC regions of interest (ROIs) Adapted from Cooper & Ritchey4 p r e d i c t i n g m e m o r y a t e v e n t o f f s e t p r e d i c t i n g m e m o r y a t e v e n t o n s e t Event transitions have been identified as key moments for organizing episodic memories, helping to segment continuous experience into discrete memory representations¹. A growing body of evidence shows that hippocampal activity and its interactions with cortical regions at the end of an event are positively associated with memory for the preceding event2-4, potentially reflecting the integration of recent experience into a bound memory trace. On the other hand, activity in content-selective regions such as the lateral occipital cortex (LOC) has been associated with memory for the current event4 (see figure below). It remains unclear how these neural responses unfold across the course of an encoding event, and whether their timing and dynamics are related to the specificity of later memory. PARADIGM ENCODING scene 3-5s scene + item 3s scene 3-5s left or right animal or object ITI 3-5s transition scene onset item onset item offset scene offset item memory 0 = forgotten 1 = remembered + features (e.g. location) ITI 2-4s covert recall 4s verbal recall 11s A gray cat in the bottom left corner... CUED RECALL item memory specificity 0 = "old" for old item and similar lure 1 = "old" for old item and "new" for similar lure old or lure ITI 2-4s response scale 1.5s sure old guess old guess new sure new sure old guess old guess new sure new item 3s similar new ITEM RECOGNITION