The role of the right language network and the multiple-demand network in verbal semantics: Insights from an Activation Likelihood Estimation Meta-analysis of 561 Functional Neuroimaging Studies

Language processing has been traditionally associated with a network of fronto-parietal and temporal regions in the left hemisphere. Nevertheless, the ‘right language network’ (frontal, temporal, and parietal regions homologous to the left language network) and the ‘Multiple-Demand Network’ (MDN) are often involved in verbal semantic processing as well, however their role remain poorly understood. This is in part due to the inconsistent engagement of these latter two networks across linguistic tasks. To explore the factors driving networks recruitment of right language network and MDN during verbal semantic processing, we conducted a large-scale Activation Likelihood Estimation meta-analysis of neuroimaging studies. We examined whether the right language network is influenced by verbal stimulus type (sentences/narratives versus single words/word pairs) and whether this may be due to differences in semantic control demands and/or the presence of social content in the stimuli. Additionally, we investigated whether MDN recruitment depends on external task demands rather than semantic control demands. Our main findings revealed greater engagement of the right language network during semantic processing of sentence/narrative stimuli, with distinct regions reflecting different functions: increased semantic control demands recruit the right inferior frontal gyrus. Instead, social content processing during a semantic task engages the right Anterior Temporal Lobe, as well as the right posterior middle temporal gyrus. Finally, semantic processing engages the MDN, but only when external task (rather than semantic) demands increase.