Abstract
Word-production theories argue that during language production, a concept activates multiple lexical candidates in left temporal cortex, and the intended word is selected from this set. Evidence for theories on spoken-word production comes, for example, from the picture-word interference task, where participants name pictures superimposed by congruent (e.g., picture: rabbit, distractor "rabbit"), categorically related (e.g., distractor "sheep"), or unrelated (e.g., distractor "fork") words. Typically, whereas congruent distractors facilitate naming, related distractors slow down picture naming relative to unrelated distractors, resulting in semantic interference. However, the neural correlates of semantic interference are debated. Previous neuroimaging studies have shown that the left mid-to-posterior STG (pSTG) is involved in the interference associated with semantically related distractors. To probe the functional relevance of this area, we targeted the left pSTG with focal repetitive transcranial magnetic stimulation (rTMS) while subjects performed a picture-word interference task. Unexpectedly, pSTG stimulation did not affect the semantic interference effect but selectively increased the congruency effect (i.e., faster naming with congruent distractors). The facilitatory TMS effect selectively occurred in the more difficult list with an overall lower name agreement. Our study adds new evidence to the causal role of the left pSTG in the interaction between picture and distractor representations or processing streams, only partly supporting previous neuroimaging studies. Moreover, the observed unexpected condition-specific facilitatory rTMS effect argues for an interaction of the task- or stimulus-induced brain state with the modulatory TMS effect. These issues should be systematically addressed in future rTMS studies on language production.
Highlights
Successful human communication requires speakers to retrieve information from long-term memory quickly and accurately
To probe the functional relevance of the left mid-to-posterior STG in semantic interference, we targeted this area with focal repetitive transcranial magnetic stimulation while healthy participants named pictures paired with congruent, categorically related, or unrelated distractors
Semantic interference and congruency facilitation effects were observed
Summary
Successful human communication requires speakers to retrieve information from long-term memory quickly and accurately. The neural correlates of this effect have remained largely unclear [12] This is certainly the case for different structures in the left temporal lobe, an area thought to play a major role in various stages of production [13]. To probe the functional relevance of the left mid-to-posterior STG (pSTG ) in semantic interference, we targeted this area with focal repetitive transcranial magnetic stimulation (rTMS) while healthy participants named pictures paired with congruent, categorically related, or unrelated distractors. We expected that focal perturbation with 10 Hz rTMS of the left pSTG region, identified in previous neuroimaging studies on semantic interference [14, 20], should interfere with word production stages, resulting in stronger semantic interference (i.e., related vs unrelated distractors) for pSTG stimulation relative to the stimulation of a control site not involved in spoken-word planning stages
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