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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 lefthanders
- 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