Poster E36, Saturday, August 18, 3:00 – 4:45 pm, Room 2000AB

Catecholaminergic modulation of the semantic processing in sentence comprehension

Yingying Tan1, Peter Hagoort1,2;1Max Planck Institute for Psycholinguistics, Nijmegen, The Netherlands, 2Donders Institute for Brain, Cognition and Behaviour Centre for Cognitive Neuroimaging, Radboud University, Nijmegen, The Netherlands

Introduction Catecholamine (CA) neurotransmitters (especially dopamine and noradrenaline) have long been implicated playing a critical role in executive control and decision making [1]. Recently, evidence from neurodegenerative patients and healthy population suggested that CA also affects language processing [2, 3]. However, the question of what kind of influence the CA might exert on language is still open. The present study investigated this question by examining the effects of 20 mg of methylphenidate (MPH), which is a catecholamine agonist, on EEG response related to semantic processing. MPH could block CA neurotransmitters reuptake and thus lead to increased extracellular CA availability. Examining the effect of MPH on semantic processing could help us better understand the neurobiological and neuropharmacological mechanisms underlying language processing. Methods 48 healthy native Dutch speakers were tested in two pharmacological conditions (MPH vs. Placebo), using a within-subject, double-blind, randomized design. In each condition, participants read 180 sentences with half of the sentences were semantically congruent while the other half sentences were not. In order to examine whether the MPH effect is goal-dependent, for half of the sentences (a block design), participants had to judge whether the sentence is semantically congruent (Semantic-task); while for the other half, participants only have to judge whether a probe word presented after the sentence was of the same font size as the sentential word (Font-task). In the latter task, processing the semantic content of the sentence was task-irrelevant. Participants’ brain responses were recorded from 28 EEG electrodes. Results & Discussion In the placebo condition, we replicated the classical N400-LPC (late positive complex) effect in the Semantic-task. Moreover, participants showed a smaller N400 effect in the Font-task than in the Semantic-task, indicating a shallower semantic processing. Most importantly, we observed an interaction of MPH×Congruency×Task in the 100–150 ms, N400, and LPC time-windows. Only in the Font-task, a stronger N400-effect was obtained in the MPH condition than in the Placebo condition. In the Semantic-task, however, the N400 effect was attenuated in the MPH condition but this attenuation might be a carryover from the earlier 100-150 ms time window. In this early time period a MPH-induced negative deflection in the semantic congruent condition was observed. In addition, the LPC effect, which was only observed in the Semantic-task, was greater in the MPH condition than in the placebo condition. Our results demonstrated a clear neuropharmacological effect on language processing. Modulations of the dopamine and/or noradrenaline levels influence sentence-level semantic processing. Results from the Font-task contradicted the general hypothesis that CA promotes goal-relevant processes, while inhibiting goal-irrelevant information. The results indicate that CA-related neurotransmitters provide a relevance signal that enhances semantic integration operations. The Basal Ganglia projections to Frontal Cortex might mediate the language processing effects of these neuropharmacological agents [4]. References [1] Cools, R., & D'Esposito, M. (2011). Biological Psychiatry, 69, 113-125. [2] Copland, D. A., et al. (2009). Cortex, 45, 943-949. [3] Grossman, M., et al., (2001). JoNS, 184, 123-130. [4] Hagoort, P. (2014). Current opinion in neurobiology, 28, 136-141.

Topic Area: Meaning: Combinatorial Semantics