Language Network

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Language Network

Main Text

TERMINOLOGY

Definitions

• Receptive language: Perception of spoken or written language
• Expressive language: Generating words and producing spoken language
• Broca aphasia: Inability to speak, word-finding difficulty, poor speech fluency, inability to organize grammar
• Wernicke aphasia: Inability to comprehend speech

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

Lateral Premotor Cortex (Exner Area)

• Extends posterior and superior from Broca area anterior to precentral sulcus (Brodmann area 6)
• Primary locus for writing language
• Required to plan motor representations associated with speech or writing

Supplementary Motor Area

• Posterior medial superior frontal gyrus near vertex (medial Brodmann area 6)
• Language SMA (pre-SMA) directly anterior to motor SMA
• Injury can cause severe language deficits that improve or resolve over weeks

Dorsolateral Prefrontal Cortex

• Middle frontal gyrus, anterior and superior to Broca area (Brodmann area 46)
• Processing of complex semantic, analytical, and abstract concepts during language

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

Cerebellar Language Regions

• Inferior vermis and posterior paramedial cerebellar hemisphere
• Typically right dominant for language
• Subtle high-level impairments in language when injured or resected

Basal Ganglia

• Variable activation of caudate and putamen on language tasks
• Lesions typically do not cause aphasia

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Tags: Imaging Anatomy Brain and Spine

Mar 13, 2021 | Posted by admin in NUCLEAR MEDICINE | Comments Off

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