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Comparing cortical alpha/beta oscillations in language production and episodic memory retrieval: an EEG study
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Poster C2 in Poster Session C, Wednesday, October 25, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Yunzhi Luo1, Britta Westner1, Vitória Piai1; 1Radboud University, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, the Netherlands
Language production involves retrieving concepts/lexical items from semantic memory, while episodic memory retrieval requires recalling details from past events. Semantic and episodic memory, both part of declarative memory, have traditionally been examined separately. Previous electrophysiological studies have consistently associated alpha-beta desynchronization with conceptual/lexical retrieval in language production and with successful episodic memory retrieval. However, it remains elusive whether the alpha-beta oscillations observed in language and memory tasks are functionally similar and can potentially index the same neuronal computations. In this ongoing EEG study, we compare conceptual/lexical retrieval in language production with episodic memory retrieval within participants. We attempt to draw a direct comparison between the alpha-beta oscillations in the language and memory tasks by comparing their oscillatory and spatial characteristics. Under our working definitions, the neural underpinning of a shared neuronal computation should be highly similar with respect to oscillatory characteristics and active brain regions. Our paradigm combines a context-driven word production task and an episodic-memory retrieval task. Participants listen to context sentences, which can either be constrained or unconstrained. After a brief retrieval period, participants are then presented with a target picture. They are instructed to name the picture and memorize it. In the constrained condition, conceptual/lexical retrieval can occur before picture presentation. Subsequently, a memory task requires participants to make old/new judgments on target or foil words, indicating whether they previously encountered the word as a picture. We computed time-frequency representations (TFR) for frequencies from 4 to 30 Hz on the two tasks and performed non-parametric cluster-based permutation tests. For the production task, we tested the contrast between constrained and unconstrained conditions. The contrast was set between correctly recognized old items and correctly rejected foils for the episodic-memory task. Within-task findings replicate the alpha-beta desynchronization effects in the language and memory tasks. In the production task, we identified a significant power decrease for the constrained compared to unconstrained conditions. This effect was most prominent in the 5-26 Hz frequency range, spanning from 0.8s to 0.3s before picture onset, in left posterior electrodes. In the episodic-memory task, a power decrease was evident for correctly recognized old items compared to correctly rejected foils. The effect was salient in the 5-21 Hz frequency range, from 0.6s to 1.5s after word onset. To further establish the similarity of these two desynchronization effects, we will compare the peak frequency within predefined electrodes in sensor space. For each participant, we will compute peak frequencies for both tasks from the left central and posterior electrodes where the alpha-beta effect was most salient in previous language studies. A Bayesian paired sample t-test will be used to evaluate whether the peak frequencies between tasks are similar. By extending the analyses to source space, we will furthermore gain insight into the spatial localization of both task effects. We hypothesize that a Bayesian t-test shows strong evidence in favor of the null hypothesis, indicating comparable peak frequencies in language and memory effects, pointing to the observed alpha-beta oscillations reflecting a shared neuronal computation.
Topic Areas: Language Production, Meaning: Discourse and Pragmatics