Evidence for hippocampal involvement in mnemonic discrimination of semantically similar verbal memory traces

Poster Session D - Monday, April 15, 2024, 8:00 – 10:00 am EDT, Sheraton Hall ABC

Alex Ilyés^1,2,3 (ilyes.alex@ttk.hu), Krisztina Cseh², Borbála Brosig^2,3, Donát Keszthelyi², György Mező^4,5, Attila Keresztes^3,2; ¹Doctoral School of Psychology, ELTE Eötvös Loránd University, Budapest, Hungary, ²Institute of Psychology, ELTE Eötvös Loránd University, Budapest, Hungary, ³Brain Imaging Centre, HUN-REN Research Centre for Natural Sciences, Budapest, Hungary, ⁴Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, Budapest, Hungary, ⁵Wigner Data Center, HUN-REN Wigner Research Centre for Physics, Budapest, Hungary

Converging evidence from computational models, as well as animal and human data suggest that hippocampal pattern separation (PS) – i.e., a neural process orthogonalizing similar neural inputs – contributes to the encoding and retrieval of highly specific memory traces. Yet, it is an open question whether PS also contributes to creating specific episodic memory traces of semantically overlapping concepts. Recently, using the semantic mnemonic similarity task (sMST), we found that mnemonic discrimination – a behavioral proxy for PS – decreased as a function of semantic similarity. In the sMST, participants first incidentally encode adjective-noun phrases, then make old-new judgements about identical and semantically highly similar phrases, where similarity is manipulated continuously using a word2vec word-embedding. Here, we extend our extant behavioral findings by directly testing the hypothesis that hippocampal PS contributes to mnemonic discrimination of memory representations with high semantic overlap. Thirty healthy young adults (Mage = 21.1 years, 15 female) completed the sMST during high-resolution functional magnetic resonance imaging that allowed us to map HC activity at the subfield level. Beyond replicating the behavioral effect that semantic similarity decreased discrimination, we observed that semantic similarity scaled encoding-related activity in the inferior parietal lobule – a key region in the neural network supporting semantic processing –, and scaled recognition-related activity in the HC. We will present currently ongoing HC subfield-level analyses testing our main hypothesis – that PS is indeed involved in mnemonic discrimination of highly similar semantic memories.

Topic Area: LONG-TERM MEMORY: Episodic