Schedule of Events | Symposia

Sketchpad Series

Foraging in conceptual spaces: neurophysiological mechanisms of mental search in semantic memory

Poster Session C - Sunday, March 30, 2025, 5:00 – 7:00 pm EDT, Back Bay Ballroom/Republic Ballroom
Also presenting in Data Blitz Session 1 - Saturday, March 29, 2025, 10:30 am – 12:00 pm EDT, Grand Ballroom.

Simone Viganò^1,2 (vigano@cbs.mpg.de), Giuliano Giari², Roberto Mai³, Christian F. Doeller^1,4, Roberto Bottini²; ¹Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ²Center for Mind/Brain Sciences, University of Trento, Rovereto, Italy, ³“Claudio Munari” Center for Epilepsy and Parkinson Surgery, Niguarda Ca’ Granda Hospital, Milan, Italy, ⁴Kavli Institute for Systems Neuroscience, Center for Neural Computation, The Egil and Pauline Braathen and Fred Kavli Center for Cortical Microcircuits, Jebsen Center for Alzheimer’s Disease, Norwegian University of Science and Technology, Trondheim, Norway

The medial temporal lobe represents both spatial and abstract relational information. However, how do we search and access stored knowledge? During navigation the hippocampal formation displays rhythmic oscillatory activity in the theta band (3-8 Hz), conveying information about traveled distance. Here we asked if this physiological signature of physical exploration also extends to mental exploration of abstract spaces, such as when recalling concepts from memory. We used stereo-EEG to record local field potentials from the hippocampus of 20 epileptic patients performing a categorical verbal fluency task, randomly “foraging” for concepts from different categories (animals, professions, or famous cities). In the period preceding the utterance of a word, when people are searching for and eventually finding a concept, the oscillatory component of hippocampal theta power was significantly higher than during or after word pronunciation. This effect was independent of the semantic category. We used linear mixed models to investigate the possibility that theta power conveys information about exploration of the semantic space, including as predictors semantic distances between words (modeled as FastText linguistic vectors) and temporal distance between utterances. We observed significant modulation when considering high-dimensional semantic distances, as well as modulation by the temporal distance between words, indicating that both temporal and spatial dimensions modulate theta power when people search for concepts in their memory. These results suggest that physiological signatures of hippocampal activity during physical exploration might also extend to mental exploration of abstract spaces, and potentially reveal novel mechanisms underlying the access of conceptual information from memory.

Topic Area: LONG-TERM MEMORY: Semantic