The extended language network: Language selective brain areas whose contributions to language remain to be discovered

Although language neuroscience has largely focused on ‘core’ left frontal and temporal brain areas and their right-hemisphere homotopes, numerous other areas—cortical, subcortical, and cerebellar—have been implicated in linguistic processing. However, these areas’ contributions to language remain unclear given that the evidence for their recruitment comes from diverse paradigms, many of which conflate language processing with perceptual, motor, or task-related cognitive processes. Using fMRI data from 772 participants performing an extensively-validated language ‘localizer’ paradigm that isolates language processing from other processes, we a) delineate a comprehensive set of areas that respond reliably to language across written and auditory modalities, and b) evaluate these areas’ selectivity for language relative to a demanding non-linguistic task. In line with prior claims, many areas outside the core fronto-temporal network respond during language processing, and most of them show selectivity for language relative to general task demands. These language-selective areas of the extended language network include areas around the temporal poles, in the medial frontal cortex, in the hippocampus, and in the cerebellum, among others. Although distributed across many parts of the brain, the extended language-selective network still only comprises ∼1.2% of the brain’s volume and is about the size of a strawberry, challenging the view that language processing is broadly distributed across the cortical surface. These newly identified language-selective areas can now be systematically characterized to decipher their contributions to language processing, including testing whether these contributions differ from those of the core language areas.