Perisylvian language networks of the human brain

TLDR

Early models of language posited a single arcuate tract linking Broca’s and Wernicke’s areas, but the varied presentations of conduction aphasia indicate a more complex perisylvian network. This study re‑examines perisylvian language connectivity with in‑vivo diffusion tensor MRI tractography. Using diffusion tensor MRI data from 11 right‑handed healthy males, the left‑hemisphere arcuate fasciculus was reconstructed via an interactive dissection technique. The authors identified a previously undescribed indirect pathway through the inferior parietal cortex that runs parallel to the classical arcuate fasciculus, providing a dual‑pathway model that accounts for conduction aphasia variability and informs evolutionary, symptom‑based, and connectionist theories of language. Published in Annals of Neurology, 2005.

Abstract

Abstract Early anatomically based models of language consisted of an arcuate tract connecting Broca's speech and Wernicke's comprehension centers; a lesion of the tract resulted in conduction aphasia. However, the heterogeneous clinical presentations of conduction aphasia suggest a greater complexity of perisylvian anatomical connections than allowed for in the classical anatomical model. This article re‐explores perisylvian language connectivity using in vivo diffusion tensor magnetic resonance imaging tractography. Diffusion tensor magnetic resonance imaging data from 11 right‐handed healthy male subjects were averaged, and the arcuate fasciculus of the left hemisphere reconstructed from this data using an interactive dissection technique. Beyond the classical arcuate pathway connecting Broca's and Wernicke's areas directly, we show a previously undescribed, indirect pathway passing through inferior parietal cortex. The indirect pathway runs parallel and lateral to the classical arcuate fasciculus and is composed of an anterior segment connecting Broca's territory with the inferior parietal lobe and a posterior segment connecting the inferior parietal lobe to Wernicke's territory. This model of two parallel pathways helps explain the diverse clinical presentations of conduction aphasia. The anatomical findings are also relevant to the evolution of language, provide a framework for Lichtheim's symptom‐based neurological model of aphasia, and constrain, anatomically, contemporary connectionist accounts of language. Ann Neurol 2005