Language Disorders

October 12, 2005

Types of Disorders

• Aphasia: acquired disorder of language due to brain damage

• Dysarthria: disorder of motor apparatus of speech• Developmental language disturbances• Associated disorders

– Alexia

– Apraxia

– Agraphia

Major Historical Landmarks

• Broca (1861): Leborgne: loss of speech fluency with good comprehension

• Wernicke (1874): Patient with fluent speech but poor comprehension

• Lichtheim (1885): classic description of aphasic syndromes

C

M A

Lichtheim’s Model

Arcuate fasciculus

Syndrome Symptom Deficit Lesion

Broca’s Aphasia speech production; sparse,

halting speech, missing function words, bound

morphemes

Impaired speech planning and production

Posterior aspects of 3rd frontal convolution

Wernicke’s Aphasia

Auditory comprehension, fluent speech, paraphasia, poor repetion and naming

Impaired representation of sound structure of words

Posterior half of the first temporal gyrus

Pure motor speech disorder

Disturbance of articulation, apraxia of speech,

dysarthria, aphemia

Disturbance of articulation Outflow from motor cortex

Pure Word Deafness

Disturbance of spoken word comprehension, repetition

also impaired

Failure to access spoken words

Input tracks from auditory cortex to Wernicke’s area

Transcortical Motor Aphasia

Disturbed spontaneous speech similar to BA; relatively preserved

repetition, comprehension

Disconnection between conceptual word/sentence representations and motor

speech production

Deep white matter tracks connecting BA to parietal

lobe

Transcortical Sensory Aphasia

Disturbance in single word comprehension with

relatively intact repetition

Disturbed activation of word meanings despite normal recognition of auditorily

presented words

White matter tracks connecting parietal and

temporal lobe

Conduction Aphasia

Disturbance of repetition and spontaneous speech,

phonemic paraphasia

Disconnetion between sound patterns and speech

production mechanisms

Arcuate fasciculus; connection between BA and

WA

Lichtheim’s (1885) Aphasic SyndromesLichtheim’s (1885) Aphasic Syndromes

Additional Aphasia SyndromesAdditional Aphasia Syndromes

Syndrome Symptom Deficit Lesion

Anomic Aphasia single-word production,

marked for common nouns; repetition and

comprehension intact

Impaired storage or access to lexical entries

Inferior parietal lobe or connections within

perisylvian language areas

Global Aphasia Performance in all language functions

Disruption of all/most language components

Multiple perisylvian language components

Isolation of the language zone

Spontaneous speech, comprehension, some

preservation of repetition; echolalia common

Disconnection between concepts and both

representations of word sounds and speech

production

Cortex outside perisylvian association cortex

Broca’s Aphasia

• Telegraphic, effortful speech

• Agrammatism

• Some degree of comprehension deficit

• Writing and reading deficits

• Repetition abnormal – drops function words

• Buccofacial apraxia, right hemiparesis

Wernicke’s Aphasia

• Fluent, nonsensical speech

• Impaired comprehension

• Grammar better preserved than in BA

• Reading impairment often present

• May be aware or unaware of deficit

• Finger agnosia, acalculia, alexia without agraphia

Conduction Aphasia

• Fluent language

• Naming and repetition impaired

• May be able to correct speech off-line

• Hesitations and word-finding pauses

• May have good reading skills

Global Aphasia

• Deficits in repetition, naming, fluency and comprehension

• Gradations of severity exist

• May communicate prosodically

• Involve (typically) large lesions

• Outcome poorest; anomic

Transcortical Aphasias

Transcortical Motor• Good repetition• Impairment in

producing spontaneous speech

• Good comprehension• Poor naming•

Transcortical Sensory• Good repetition• Fluent speech• Impaired

comprehension• Poor naming• Semantic associations

poor

Associated Deficits

• Alexia without Agraphia– Impairment in reading with spared writing

• Apraxia– Loss of skilled movement not due to weakness

or paralysis

Fundamental Lessons

• Language processors are localized

• Different language symptoms can be due to an underlying deficit in a single language processor

• Language processors are regionally associated with different parts of the brain in proximity to sensory or motor functions

What Language Disorders RevealWhat Language Disorders Reveal about Underlying Processes about Underlying Processes

• Pure Word Deafness: selective processing of speech sounds implies a specific speech-relevant phonological processor

• Transcortical Sensory Aphasia: repetition is spared relative to comprehension; selective loss of word meaning; some cases suggest disproportionate loss of one or more categories

What Language Disorders RevealWhat Language Disorders Reveal about Underlying Processes about Underlying Processes

• Aphasic errors in word production: reveal complex nature of lexical access– Phonological vs. semantic errors: independent vs. interactive

relationship?– Grammatical class: nouns vs. verbs (category specificity)

• Broca’s aphasia: syntax comprehension and production– Central syntactic deficit; loss of grammatic knowledge– Problems in “closed-class” vocabulary (preposition, tense

markers)– Limited capacity account– Mapping account (inability to map from parsing to thematic

roles)

Aphasia and the Semantic System

• Meaning stored separately from form

• Models of representation in semantics– Feature-based models (see categorization)– Nondecompositional meaning

• Modality-specific semantic deficits: optic aphasia as an example

Two Models of Semantic Organization

One Semantic System

Multiple Semantic Systems