1 - University of Arizona
1. Major neural substrates of expressive and receptive language processes
- language is localized to the left hemisphere in 95% or right-handed people and in most left-handers
- about 15% of left-handed people are right hemisphere dominant for language and 15% have bilateral representation for language
- Broca’s area: opercular/triangular parts of inferior frontal gyrus; planum temporale ( superior surface of temporal lobe behind auditory cortex
- Wernicke’s area: posterior superior temporal gyrus; angular/supramarginal gyri
- Broca’s area, Wernicke’s area, and their connection the arcuate fasciculus ( perisylvian (located around left sylvian fissure, the lateral sulcus)
- arcuate fasciculus necessary to repeat something heard
- some aspects of language rely on extrasylvian regions of left hemisphere (and right hemisphere)
Compare/contrast areas involved in processing of sound and production of speech
Comprehension of Language
- auditory pathway involves cochlea, CN VIII, brainstem, bilaterally after cochlear nuclei ( lateral lemniscus ( inferior colliculus ( inferior brachium ( thalamus, MGN ( internal capsule ( primary auditory cortex; auditory info from primary auditory areas ( projects to Wernicke’s area
- visual pathway for written language involves the retina ( optic nerve ( optic tract ( LGN of thalamus ( internal capsule ( primary visual cortex in occipital lobe; higher level processing of written info relies on adjacent areas in the temporo-parietal association areas
Production of Language
Speech
- speech production involves moving muscles, bones, and cartilage involved in articulation, in lower airway, larynx, pharynx, and mouth; speech is the motor act that carries the linguistic message
- dysarthria refers to imprecise articulation due to muscle weakness or incoordination resulting from damage to motor areas (motor cortex, basal ganglia, cerebellum, UMN, LMN, NMJ, or muscle)
- Apraxia of speech ( motor speech disorder reflecting impaired motor programming for speech that results in difficulty planning and sequencing sound
Language
- representation of conceptual knowledge in left inferior temporal lobe and left inferior frontal lobe
- ability to retrieve words or name things can be disrupted by damage to perisylvian or extrasylvian regions of the left hemisphere
- Expressive language formulation involves Broca’s area; Broca’s area critical for motor planning for speech production (verbal output) as well as syntactic (word ordering) aspects of language
- written language ( network including posterior temporal lobe (spelling) and fronto-parietal regions involved in motor planning and control of the hand
2. Aphasia
- acquired language deficit characterized by impaired word selection, language production, and language comprehension
- paraphasia ( incorrect word choice and sound substitution
- alexia ( reading impairment
- agraphia ( writing impairment
- common causes include ischemic stroke of left middle cerebral artery ( blood to perisylvian cortical language areas
- extrasylvian aphasias are called transcortical aphasias; lesions here are isolated from regions involved in semantic processing and production of volitional speech
- slow onset from brain tumors or focal cortical atrophy
- transient ischemic attacks (TIA), migraine, seizures ( transient aphasia
3. Aphasia classification
- based on fluency, auditory comprehension, repetition, and naming
Fluency
- fluent aphasias ( good verbal output consisting of well-articulated utterances of normal length and prosody (variations of pitch, loudness, rhythm)
- fluent aphasias associated with posterior lesions (Wernicke’s) that spare anterior cortical regions for motor control of speech (Broca’s)
- nonfluent aphasias ( sparse, effortful utterances of short phrase length and disrupted prosody; struggle with articulation; few nouns, ever fewer verbs; associated with anterior lesions comprising motor and premotor cortical regions involved in speech production (Broca’s)
Auditory comprehension
- usually defective in most aphasias to some degree; anterior lesions result in minor impairments; posterior lesions result in significant impairment of auditory processing
Repetition
- repetition of spoken words requires an intact perisylvian region (Wernicke’s, Broca’s, and arcuate fasciculus); lesions anywhere in perisylvian region disrupt repetition
- extrasylvian region lesions have preserved repetition, but reduction of spontaneous speech, comprehensions disturbance, or both
Naming
- anomia is word finding difficulties; can occur in isolation in anomic aphasia
- perseveration is repetition of word
- neologism is making up a word (and perhaps repeating it)
Classic Aphasia Syndromes
- look at table on next page
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