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要旨:
Introduction: Conceptual knowledge is central to numerous cognitive abilities, such as word comprehension. The left posterior inferior parietal lobe (pIPL) is consistently activated in neuroimaging studies on conceptual processing regardless of the concepts” content, suggesting that it represents a multimodal hub for conceptual knowledge. For example, we previously showed that left pIPL is engaged during the retrieval of both sound and action features of word meaning. However, as neuroimaging is correlational, it remains unknown whether left pIPL plays a causal role in multimodal conceptual processing.
Objectives: We aimed to determine whether left pIPL is functionally relevant for the processing of action and/or sound features of concepts, and to what extent such causal involvement depends on the task.
Materials & methods: We applied 10 Hz online repetitive transcranial magnetic stimulation (rTMS; 4 pulses at 100% resting motor threshold) over left pIPL or sham rTMS, while 26 participants performed three different tasks—lexical decision, sound judgment, and action judgment—on words that exhibited a high or low association with sounds and actions (e.g. “telephone” is a high sound–high action word).
Results: A repeated-measures ANOVA on sham-normalized accuracies showed a 3-way interaction of task, sound association, and action association. Step-down analyses (using marginal means) revealed that rTMS over left pIPL selectively impaired response accuracy for action judgments on low sound–low action words, as compared to sham stimulation (t = −3.18, p = 0.006; Bonferroni-corrected) (Fig. 1). Accuracy during lexical decisions or sound judgments was not significantly affected by TMS. Response times were also not significantly altered.
Conclusion: Our results indicate that left pIPL is causally involved in the processing of action features of concepts selectively when these are task-relevant. TMS seems to have increased action-related activity in the pIPL, leading to a higher likelihood to judge an object as action-related. The fact that high-sound words were not affected suggests that sound features enable compensation for disruption of action processing via sound-action coupling. The absence of TMS effects during lexical decisions indicates that left pIPL specifically supports tasks that require access to conceptual knowledge. The lack of a significant impairment of sound judgments might reflect that (1) left pIPL is not causally involved in sound feature retrieval; (2) pIPL stimulation concomitantly affected nearby action-relevant regions, leading to a predominant disruption of action features; or (3) other sound-relevant regions compensated for the perturbation by increasing their functional contribution.
