Comprehension of Ambiguous Idioms in Prefrontal Cortex: Evidence from rTMS

The cognitive processes related to idiom comprehension have been predominantly associated with neural mechanisms and conceptual mapping processes controlled by the dorsolateral prefrontal cortex (DLPFC). Although the role of the DLPFC in idiom comprehension has been extensively studied, ambiguous idioms—those with more than one acceptable meaning—have been relatively understudied in the neuroscientific literature. This study explores how the left and right DLPFC contribute to resolving ambiguous idioms, with a focus on understanding the neural mechanisms underlying conceptual mapping during the comprehension of such idioms. In the study, the left and right DLPFC regions of 15 native Turkish-speaking participants were temporarily inhibited using repetitive transcranial magnetic stimulation (rTMS) to examine the role of prefrontal areas in the brain in resolving ambiguous idioms. Following the brain stimulation, participants engaged in an experiment that required them to interpret both literal sentences without figurative meaning and ambiguous idiomatic expressions in which all figurative interpretations were meaningful and plausible. The findings revealed that when left DLPFC was suppressed, participants' ability to accurately comprehend the figurative meanings of ambiguous idioms was significantly impaired, as evidenced by increased reaction times and decreased accuracy rates. In contrast, no significant impairment in processing ambiguous idioms was observed when the right DLPFC was suppressed. These findings suggest that the cognitive load involved in processing ambiguous idioms with multiple acceptable meanings is predominantly managed by the left hemisphere. This study provides insight into the functions of both the right and left prefrontal areas of the brain during the resolution of ambiguous linguistic units, offering further understanding of lateralization, a key phenomenon in the neuroscientific processes of language comprehension.