Converging Language Streams in the Human Temporal Lobe

TLDR

After initial unimodal processing, spoken and written language converge to access verbal meaning, yet the cortical locus of this convergence remains disputed—aphasic stroke studies localize it to posterior temporal and inferior parietal cortex, neurodegenerative evidence implicates anterior temporal cortex, and prior imaging has failed to reconcile these positions. Using fMRI with spoken and written narratives and multiple baselines, the study identified shared activation in the inferior and lateral left anterior temporal cortex and at the temporal‑occipital‑parietal junction during implicit comprehension. The results demonstrate that verbal comprehension relies on unimodal processing streams that converge in both anterior and posterior heteromodal regions of the left temporal lobe.

Abstract

There is general agreement that, after initial processing in unimodal sensory cortex, the processing pathways for spoken and written language converge to access verbal meaning. However, the existing literature provides conflicting accounts of the cortical location of this convergence. Most aphasic stroke studies localize verbal comprehension to posterior temporal and inferior parietal cortex (Wernicke’s area), whereas evidence from focal cortical neurodegenerative syndromes instead implicates anterior temporal cortex. Previous functional imaging studies in normal subjects have failed to reconcile these opposing positions. Using a functional imaging paradigm in normal subjects that used spoken and written narratives and multiple baselines, we demonstrated common activation during implicit comprehension of spoken and written language in inferior and lateral regions of the left anterior temporal cortex and at the junction of temporal, occipital, and parietal cortex. These results indicate that verbal comprehension uses unimodal processing streams that converge in both anterior and posterior heteromodal cortical regions in the left temporal lobe.