Language Network
Main Text
TERMINOLOGY
Definitions
IMAGING ANATOMY
Overview
- • Language involves complex network of frontal, parietal, and temporal regions; typically left hemisphere dominant
- • Bilaterality or right dominance of language in 5% of right-handed and 22% of left-handed or ambidextrous individuals
- • Higher incidence of bilaterality or right dominance in psychiatric and developmental disorders, including autism and schizophrenia
- • Core regions for presurgical mapping are Broca area, Wernicke area, supplementary motor area (SMA), and lateral premotor (Exner) area; injury of many other areas may produce more subtle language deficits
Broca Area
- • Posterior left inferior frontal gyrus bordering operculum (Brodmann areas 44, 45): Pars opercularis and pars triangularis
- • Primary locus of expressive language, creating syntax, and production of meaningful language
- • Overlapping spatial distribution of syntax, phonology, and grammar-processing subregions
- • Word selection processed more anteriorly, articulatory planning more posteriorly
Wernicke Area
- • Posterior superior temporal gyrus, posterior superior temporal sulcus, and posterior middle temporal gyrus (posterior Brodmann area 22)
- • Primary locus of receptive language, phonological processing, and speech perception
- • Semantic meaning also processed in adjacent angular, supramarginal, and middle temporal gyri
Default Mode Network
- • Stores autobiographical knowledge of self, objects, people, events, culture; processes internal narrative
- • Interfaces with core language regions to process contextual meaning of language
- • Distributed network, including angular gyrus (temporoparietal junction), posterior cingulate (precuneus), medial prefrontal cortex, middle and inferior temporal gyri
- • Connections between default mode network and core language areas are left lateralized
- • Focal lesions typically do not produce aphasia
- • Default mode regions not activated on most fMRI language tasks
Auditory Cortex
- • Superior temporal gyrus, including Heschl gyrus (Brodmann areas 41, 42)
- • Between Broca and Wernicke areas on axial slices
- • Surrounded by auditory association cortex for progressively higher level auditory perception
- • Auditory/motor integration in posterior temporoinsular junction often activated by language tasks
Visual Cortex
- • Primary visual cortex (V1): Pericalcarine occipital pole (Brodmann area 17)
- • Secondary visual cortex (V2, V3, V4, V5/MT, Brodmann areas 18 and 19) surrounds V1
- • Lingual occipital gyrus and lateral occipital cortex: Recognition and processing of written letters and symbols
- • Inferior lateral temporooccipital cortex and angular gyrus both involved in reading
Accessory Inferior Temporal and Occipital Language Regions
- • Basal temporal language area (BTLA) (a.k.a. visual word form area) has been proposed in mid-left fusiform gyrus
- • Likely not specific to language but may be involved in letter and word recognition
- • No permanent severe language deficits expected from unilateral BTLA injury
- • Lingual gyrus more associated with global shape processing of letters; fusiform gyrus associated with local shape processing of letters
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