The language network is recruited but not required for non-verbal semantic processing

Consistent with longstanding findings from neuropsychology, several brain regions in left frontal and temporal cortex respond robustly and selectively to language. These regions, often referred to as the "language network", respond more strongly to meaningful stimuli (like words and sentences) than to stimuli devoid of meaning (like pseudowords and Jabberwocky sentences). But are these regions selectively recruited in processing linguistic meaning? Or do they instead store and/or process complex semantic information independent of its format (sentences or pictures)? In Experiment 1, we scanned participants with fMRI while they performed a semantic plausibility judgment task vs. a difficult perceptual control task on sentences and line drawings that describe/depict simple agent-patient interactions. We found that the language regions responded more strongly when participants performed the semantic task compared to the perceptual task, for both sentences and pictures (although sentences elicited overall stronger responses). Thus, healthy adults engage language regions when processing non-verbal meanings. But is this engagement necessary for understanding pictorial depictions of events? In Experiment 2, we tested two individuals with global aphasia, who have sustained massive damage to perisylvian language areas and display severe language difficulties, together with a group of control participants. Individuals with aphasia were at chance on a task of matching the sentences and pictures. However, they performed close to controls in assessing the plausibility of pictorial depictions of agent-patient interactions. Taken together, these results indicate that the left fronto-temporal language system is recruited but not necessary for processing complex non-verbal meanings.