Chapter 7: Language

Language processing involves distributed neural networks across the cortex rather than localization in a single region, with organization heavily influenced by individual handedness. Right-handed individuals typically show left hemisphere language dominance in approximately 95 to 96 percent of cases, while left-handed individuals often exhibit more bilateral representation and consequently experience different patterns of recovery following brain injury. The widely adopted Boston classification and Wernicke-Geschwind model provide essential frameworks for understanding how language moves from sensory input to motor output through interconnected structures including Broca's area in the inferior frontal cortex for speech production, Wernicke's area in the superior temporal lobe for semantic comprehension, the arcuate fasciculus connecting these regions, and the angular gyrus for translating between visual and auditory language forms. Six major aphasia types demonstrate distinct profiles: Broca's aphasia produces slow telegraphic speech with preserved comprehension, Wernicke's aphasia generates fluent but meaningless output with impaired comprehension, conduction aphasia selectively disrupts repetition while preserving other functions, anomic aphasia specifically affects word retrieval, transcortical aphasias preserve repetition despite other severe deficits, and global aphasia devastates all language functions. Reading and writing disorders, termed alexia and agraphia respectively, can occur alongside aphasias or independently and are understood through cognitive models such as the dual-route framework, which explains patterns like deep dyslexia with semantic errors, phonological dyslexia affecting nonword reading, surface dyslexia impairing irregular word recognition, and letter-by-letter reading requiring explicit phonemic decoding. Clinical assessment employs standardized instruments such as the Boston Diagnostic Aphasia Examination to evaluate fluency, comprehension, repetition, and naming abilities, while rehabilitation outcomes depend on injury etiology and severity, with most spontaneous recovery occurring within three to six months post-injury and therapeutic approaches including stimulation techniques, linguistic instruction, and melodic intonation therapy.