How Extended Is Wernicke's Area? Meta-Analytic Connectivity Study of BA20 and Integrative Proposal

Abstract

Understanding the functions of different brain areas has represented a major endeavor of contemporary neurosciences. The purpose of this paper was to pinpoint the connectivity of Brodmann area 20 (BA20) (inferior temporal gyrus, fusiform gyrus) in language tasks. A meta-analysis was conducted to assess the language network in which BA20 is involved. The DataBase of Brainmap was used; 11 papers corresponding to 12 experimental conditions with a total of 207 subjects were included in this analysis. Our results demonstrated seven clusters of activation including other temporal lobe areas (BA3, BA21), the insula, and the prefrontal cortex; minor clusters in the cingulate gyrus and the occipital lobe were observed; however, the volumes of all the activation clusters were small. Our results suggest that regardless of BA20 having certain participation in language processes it cannot be considered as a core language processing area (Wernicke's area); nonetheless, it could be regarded as kind of language processing marginal area, participating in "extended Wernicke's area" or simply "Wernicke's system." It is suggested that "core Wernicke's area" roughly corresponds to BA21, BA22, BA41, and BA42, while a "language associations area" roughly corresponds to BA20, BA37, BA38, BA39, and BA40 ("extended Wernicke's area" or "Wernicke's system").

Figure 1

Functional connectivity map of BA20 by Meta-Analytic Connectivity Modeling. (a) Transversal descending cuts of the brain MRI template. Left hemisphere appears on the left side (neurological convention). Clusters of activation are color coded for statistical significance from dark blue (lowest) to red (highest). (b) 3D volumetric rendition of the brain showing activation on the left hemisphere surface. Red color zone identifies BA20. Deep and midline activations are shown.