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How Representational Geometry Aligns Between Brains and Anchors to Semantics During Live Verbal Communication

Poster Session C - Sunday, March 8, 2026, 5:00 – 7:00 pm PDT, Fairview/Kitsilano Ballroom
Also presenting in Data Blitz Session 4 - Saturday, March 7, 2026, 10:30 am – 12:00 pm PST, Salon F.

Yulei Shen¹ (), Takahiko Koike¹; ¹Inter-Individual Brain Dynamics Collaboration Unit, Center for Brain Science, RIKEN.

While previous hyperscanning studies have demonstrated inter-brain temporal synchrony, it remains unclear whether neural representational geometry aligns during live communication and whether such alignment relates to the linguistic information being exchanged. This fMRI hyperscanning study with 29 sender-receiver dyads directly addresses this question. In each trial, senders viewed an image and generated five sentences based on five given keywords to enable receivers—who had no access to the image—to mentally reconstruct it. We examined inter-brain alignment during the 15-second real-time interaction by computing cross-trial RDMs within sliding time windows. First, we assessed neural-to-neural representational geometry alignment by measuring time-resolved correspondence and the receiver's progressive convergence toward the sender's geometry, comparing real dyads with pseudo-partner controls. Real dyads exhibited significantly stronger, interaction-specific, time-dependent increases in neural-to-neural alignment across bilateral language areas (L-IFG, bi-STG/MTG, R-AG), left executive control regions (SFG, SMG), and right visuo-attentional cortex (IPL, LOC). Second, we tested whether this progressive inter-brain alignment is directly grounded in the linguistic content using language embeddings (BERT) derived from senders' descriptions. Senders progressively anchored their neural geometry to their own semantic models, engaging bilateral visual-memory networks (L-LG, L-PhG, L-PCu; R-FG, R-AG). Receivers showed increasing semantic anchoring to the sender's linguistic embeddings over time, engaging left attention-control (SFG, SMG) and right temporo-occipital regions (IOG, FG, TP), but this effect was not interaction-specific. These findings demonstrate that authentic communication progressively aligns inter-brain representational geometry through linguistic grounding. The divergent semantic anchoring patterns between senders and receivers reveal distinct neural mechanisms underlying this representational coupling.

Topic Area: LANGUAGE: Semantic