Search Abstracts | Symposia | Slide Sessions | Poster Sessions
Transcranial ultrasound stimulation over the left inferior frontal gyrus perturbs sentence processing
Poster Session E, Friday, October 2, 11:00 am - 1:00 pm, Wangari Maathai
Guang Yang1, Luyao Chen1, Xingfang Qu3, Xieanni Shan4, Dongwei Li4, Ke Zeng4, Yifei He5, Gesa Hartwigsen6, Robert Chen7, Angela D. Friederici2; 1The Hong Kong Polytechnic University, 2Max Planck Institute for Human Cognitive and Brain Sciences, 3The University of Hong Kong, 4Beijing Normal University, 5Marburg University, 6Leipzig University, 7University of Toronto
Introduction: The left inferior frontal gyrus (LIFG) and left posterior temporal lobe (LpTL) are both implicated in sentence processing, but direct causal comparisons between these regions remain limited. We tested whether transcranial ultrasound stimulation (TUS) over LIFG or LpTL perturbs comprehension of hierarchically structured Mandarin sentences while minimizing semantic-conceptual familiarity. Methods: Thirty-six healthy right-handed native Mandarin speakers completed a within-subject, three-session experiment with at least 7 days between sessions. In separate sessions, offline theta-burst TUS was applied over LIFG, LpTL, or vertex as an active control site, with the order of stimulation sites counterbalanced across participants. Participants then read semantically unnatural but well-structured sentences composed of geometric-shape nouns and action verbs. Materials included complex sentences with embedded relative clauses and simpler coordinated sentences. On each trial, participants answered a two-choice probe question about thematic-role relations. Reaction times (RTs) and accuracy were analyzed with mixed-effects models. Hierarchical drift-diffusion modeling (HDDM) was used to test whether stimulation effects reflected changes in evidence accumulation, response caution, or non-decision time. Results: LIFG TUS impaired sentence processing relative to the other stimulation sites. RTs showed a main effect of stimulation region, F(2) = 4.160, p = 0.023. LIFG TUS significantly slowed responses relative to LpTL TUS, b = 0.020, SE = 0.007, t = 2.860, p = 0.013, and showed marginal slowing relative to vertex TUS, b = 0.014, SE = 0.006, p = 0.068. Accuracy also showed a main effect of stimulation region, χ²(2) = 12.860, p = 0.002, with lower accuracy after LIFG TUS than after LpTL stimulation, p = 0.009, and vertex stimulation, p = 0.001. Complex sentences elicited longer RTs and lower accuracy than simple sentences, but stimulation region did not significantly interact with sentence complexity. HDDM model comparison favored a model in which drift rate varied across conditions. Relative to vertex, LIFG stimulation decreased drift rate, mean = -0.140, 94% HDI [-0.280, -0.090], indicating less efficient evidence accumulation, whereas LpTL stimulation did not produce a corresponding behavioral impairment. Conclusion: These findings provide causal evidence that perturbing the LIFG, but not the LpTL, disrupts sentence-level processing when semantic familiarity is minimized. More broadly, the results demonstrate the feasibility of using TUS to modulate sentence-level language processing in healthy adults. The HDDM results further indicate that LIFG stimulation impaired evidence accumulation during decisions about “who did what to whom,” a key process in sentence parsing.
Topic Areas: Syntax and Combinatorial Semantics, Methods