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Poster D45, Thursday, November 9, 6:15 – 7:30 pm, Harborview and Loch Raven Ballrooms

Effect of methylphenidate on semantic unification: Evidence from an EEG study in the healthy population

Yingying Tan1, Peter Hagoort1;1Max Planck Institute for Psycholinguistics

Methylphenidate is the most frequently prescribed medication for people with ADHD. Nowadays, there is an increasing use of methylphenidate in the healthy population, because many studies showed that methylphenidate could enhance cognitive functions in both ADHD and healthy populations, such as working memory (WM) and response inhibition. However, the cognitive-enhancing effect of methylphenidate is under debate and some recent studies suggested that the effect of methylphenidate depends on specific tasks demands and individual differences [1, 2]. So far, there is no empirical study examining the effect of methylphenidate in sentence processing in the healthy population. Given the long-studied link between WM and language processing and the important role of dopamine in language processing [3], we aimed to investigate the effect of methylphenidate on semantic unification during sentence comprehension. This study used a within-subject double-blind randomized placebo-controlled design. 48 healthy native Dutch speakers were recruited and each subject was tested in two sessions. There are three within-subject experimental manipulations: drug (methylphenidate vs. placebo), sentences' semantic congruence, and task type. Half of the subjects received an oral capsule of 20 mg methylphenidate in session 1 while the other half subjects received a placebo, and each subject received the other kind of capsule in session 2. During each session, subjects were instructed to read 180 sentences followed by question. The sentences were either semantically congruent or incongruent, e.g., “Dutch trains are yellow/*sour.” For the following questions, subjects have to judge whether the sentence is semantically congruent in one block and whether a probe word presented after the sentence is of the same font size as the sentence word in another block. Subjects’ brain responses were recorded from 32 active EEG electrodes. We examined the methylphenidate effect on semantic unification as indexed by change on the N400 component [4]. The behavioral results showed that after taking methylphenidate, subjects are more sensitive to semantic violation and font size changes in both tasks as indexed by a significantly higher d’. The preliminary EEG data showed that there is an interaction of methylphenidate and task type on the N400 component. After taking methylphenidate, subjects showed a comparable N400 component in both tasks. However, in the placebo condition, the scalp distribution of the N400 component differed between the two tasks. The current results suggested that methylphenidate affects semantic unification during sentence comprehension. We are further examining the EEG data and check whether the methylphenidate effect is related to subjects’ WM or baseline dopamine level. References [1] Fallon, S. J., & Cools, R. (2014). Reward acts on the pFC to enhance distractor resistance of working memory representations, JoCN, 26, 2812 - 2826. [2] Cools, R., & D'Esposito, M. (2011). Inverted-U-shaped dopamine actions on human working memory and cognitive control. Biological Psychiatry, 69, e113-125. [3] Grossman, M., et al., (2001). Dopamine supports sentence comprehension in Parkinson's Disease, JoNS, 184, 123-130. [4] Kutas, M., & Federmeier, K. D. (2011). Thirty years and counting: finding meaning in the N400 component of the event-related brain potential (ERP). Annual review of psy, 62, 621-647.

Topic Area: Meaning: Lexical Semantics

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