The involvement of left inferior frontal and middle temporal cortices in word production unveiled by greater facilitation effects following brain damage

Abstract

In stroke-induced aphasia, left hemispheric lesions generally disturb the word production network. The left inferior frontal gyrus (LIFG) and the left middle temporal gyrus (LMTG) are involved in word production, but their respective contribution remains ambiguous. Previous investigations have largely focused on semantic interference to gather information about word production. Here we assessed the sensitivity of twenty-five aphasic speakers with either LIFG or LMTG lesions and matched controls to both semantic facilitation and interference in word production using the picture-word (PWP) and the blocked-cyclic naming (BCNP) paradigms. In the PWP (Exp. 1), semantic facilitation was exaggerated in participants with LIFG damage as compared to age-matched controls. In the BCNP (Exp. 2), repetition priming on production speed was larger in participants with LMTG damage than in controls, without any decrease of semantic errors. In the light of the results in the PWP, the LIFG appears to be a necessary structure to shape semantic facilitation. It might play an important role in properly adjusting the lexical selection threshold within the word production network. The results in the BCNP suggest that the LMTG conveys semantic-to-lexical connections likely involved in repetition priming and in mapping concepts to their correct lexical label. As consequences, participants with LIFG lesions possibly rely more on strategic vs automatic processes to efficiently select lexical entries in semantically competitive contexts, whereas participants with LMTG might exploit residual semantic-to-lexical activation.

Keywords: Aphasia; Language production; Left inferior frontal cortex; Left middle temporal cortex; Semantic priming.