Review Neuronal basis of speech comprehension Karsten Specht a, b a Department of Biological and Medical Psychology, University of Bergen, Jonas Lies vei 91, 5009 Bergen, Norway b Department for Medical Engineering, Haukeland University Hospital, Bergen, Norway article info Article history: Received 15 May 2013 Received in revised form 15 September 2013 Accepted 19 September 2013 Available online 7 October 2013 abstract Verbal communication does not rely only on the simple perception of auditory signals. It is rather a parallel and integrative processing of linguistic and non-linguistic information, involving temporal and frontal areas in particular. This review describes the inherent complexity of auditory speech comprehension from a functional- neuroanatomical perspective. The review is divided into two parts. In the first part, structural and functional asymmetry of language relevant structures will be discus. The second part of the review will discuss recent neuroimaging studies, which coherently demonstrate that speech comprehension pro- cesses rely on a hierarchical network involving the temporal, parietal, and frontal lobes. Further, the results support the dual-stream model for speech comprehension, with a dorsal stream for auditory- motor integration, and a ventral stream for extracting meaning but also the processing of sentences and narratives. Specific patterns of functional asymmetry between the left and right hemisphere can also be demonstrated. The review article concludes with a discussion on interactions between the dorsal and ventral streams, particularly the involvement of motor related areas in speech perception processes, and outlines some remaining unresolved issues. This article is part of a Special Issue entitled <Human Auditory Neuroimaging>. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction This review article summarises the neuronal basis of speech comprehension in terms of functional-neuroanatomy. Specific as- pects include the structural and functional asymmetry in the temporal and frontal lobe, as well as along the proposed ventral stream for auditory speech perception. It is possible only to sum- marise a fraction of the available literature, and so the review fo- cuses on the underlying anatomical structures. I therefore focus mainly on a review of the fMRI literature, whist at the same time acknowledging the valuable contribution of electrophysiological studies to this field. The review is divided into two main parts. The first part describes the neuroanatomical basis in terms of functional neuroanatomy, and structural and functional asymmetry. The sec- ond part focuses on the well-accepted dual-stream model of the functional anatomy of language (Hickok and Poeppel, 2007). The ventral stream is proposed as the dominant stream for speech comprehension. It interacts closely with the dorsal stream, which plays an important role in speech production. This review article concludes with a brief summary and an outlook on unresolved issues, related to the current version of the dual-stream model. 1.1. Anatomical basis of the speech and language network Since the 19th century, it has been established that the left hemisphere is crucial for speech perception, processing, and pro- duction. Previous models of speech processing, like the Wernickee Lichtheim model (Lichtheim, 1885; Wernicke, 1874), have sug- gested a cortical network comprising Wernicke’s area, Broca’s area, a third, anatomically less specified area for processing of concepts, and the connections between. Anatomically, Wernicke’s area is typically defined as the posterior part of the superior temporal gyrus, including the planum temporale (PT), which is a cortical structure on the superior surface of the superior temporal gyrus, just behind the primary auditory cortex, i.e. Heschl’s gyrus (see Fig. 1). Clear anatomical landmarks or cytoarchitectonic de- scriptions do not circumscribe Wernicke’s area, thus there are varying definitions of Wernicke’s area. By contrast, Broca’s area in the left inferior frontal gyrus (IFG) is clearly defined by the un- derlying cytoarchitectonic areas, labelled as Brodmann area (BA) 44 E-mail address: Karsten.specht@psybp.uib.no. Contents lists available at ScienceDirect Hearing Research journal homepage: www.elsevier.com/locate/heares 0378-5955/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.heares.2013.09.011 Hearing Research 307 (2014) 121e135