Language Why language is hard to study Aphasia classification: which patterns of deficits run together? Older vs. Newer Models of Language Organization Language re-organization following early injury

What is language Many animals use simple sounds for communication What is line between simple communication and language? What makes human language unique? Use of word as referents for things or ideas ordering of words in different ways to alter meaning

What is required for language? Interaction of memory with sensory input and motor output systems Memory Phonological Orthographic semantic Sensory Auditory processing Visual processing Tactile processing (braille) Motor articulation, writing, signing or drawing

Components of language Phoneme: individual sound units Grapheme: the written form used to represent phoneme(s) Morphemes: smallest meaningful units of a word, in combination creates words Syntax: admissible combinations of words in phrases and sentences (grammar) Lexicon: the collection of all words in a given language, mental “dictionary” Semantics: the meanings that correspond to all lexical items and possible sentences

Components of language Morphology: study of how and why words take on certain structure and how that affects semantics and syntax Pragmatics: social rules governing how language is used Prosody: vocal intonation that can modify the literal meaning of words and sentences Discourse: linking of sentences such that they constitute a narrative

Language and the brain: functional segregation? Syntax Speaker Identity Phrases Prosody Words Morphemes Meaning Intent Phonemes

The Challenge of Language Research Unique human ability animal communication systems have more limited combinatorial repertoire limits study of brain behavior relationships to humans There are no adequate animal models of language Makes completely controlled experiments impossible Purposeful lesion studies are obviously unethical The closest approximation is birdsong, but Vocalizations of birds are significantly less complex Many structures within the human brain do not have homologues in the avian brain

Aphasia: Window into the organization of language function The left hemisphere of Paul Broca’s patient “Tan”

Paul Broca- localization of language production Early work on aphasia Paul Broca- localization of language production Broca’s aphasia, motor, expressive, or non-fluent aphasia Difficulty speaking : slow, deliberate, simple grammar structure, “telegraphic” Melodically flat Comprehension intact Damage to left frontal (lower posterior)

Examples of Broca’s Aphasia

Carl Wernicke- localization of language comprehension Early work on aphasia Carl Wernicke- localization of language comprehension Wernicke’s aphasia, receptive, fluent aphasia Speech production is intact Speech flows without hesitation Appropriate intonation Comprehension impaired Speech is “meaningless” Damage to left temporal (superior and posterior)

Examples of Wernicke’s Aphasia

Classical Aphasia Syndromes Fluent Speech? YES NO Intact Comprehension? YES NO YES NO Intact Repetition? YES NO YES NO YES NO YES NO Anomic Conduction Trans- Cortical Sensory Wernicke Trans- Cortical Motor Broca Mixed Trans- Cortical Global

Damage Associated with Common Aphasic Syndromes Wernicke Broca Global Conduction

Pure Aphasias Alexia without agraphia Agraphia Word deafness Normal speech, normal writing, poor reading Agraphia Normal speech, poor writing Word deafness Normal speech, poor comprehension, poor repetition

Clinical Assessment of Aphasia Subtests of the Boston Diagnostic Aphasia Exam: Boston Naming Test- patient required to name various pictures that vary in terms of frequency, animacy, etc… Responsive naming- “what do we tell time with?” and “what color is grass?”

Boston Naming Errors ‘water bird in Florida’ Type Circumlocution Perceptual Semantic Paraphasia Phonemic Neologism Aphasia Syndrome Anomic Wernicke and Transcortical Sensory ‘water bird in Florida’ ‘thing you lie in in summer’ ‘rough skin, from Africa’ ‘helmet’ ‘fishing net’ ‘pig’ ‘duck’ ‘bed’ ‘elephant’ ‘pemlican’ ‘hannock’ ‘rhisocerus’ ‘palifrene’ ‘habiteller’ ‘cantifron’

Tests of Expression Subtests of the BDAE: Oral Agility Verbal Agility Automatic Sequences Mean length of utterance

Tests of comprehension Subtests of the BDAE: Basic word discrimination Commands Complex ideational material

Tests of repetition Subtests of the BDAE: Single word repetition Single pseudoword repetition Repetition of sentences

BDAE Profiles Broca’s Wernicke’s

The Wernicke-Geschwind (neurological) model

Limitations of Classical Approach Based on observations of (mostly) acute stroke patients Up to 49% of aphasics are unclassifiable Broca’s aphasics have trouble understanding syntax in non-standard word order Does not account for complexities of normal language processing and other dissociations

Limitations of lesion studies I Lesions are often extensive and may damage connection fibers No two lesions (or patterns of behavioral impairment) are exactly alike, making comparisons across subjects inherently imprecise Due to the structure of the vasculature, some areas are never selectively damaged by stroke

Limitations of lesion studies II We do not yet fully understand mechanisms of plasticity following damage to the brain Patients may have adopted compensatory strategies, so their behavioral performance is not truly reflective of their cognitive deficit 25

Psycholinguistic Models Explain normal language processing Account for broader range of language deficits Less constrained by anatomic considerations Price, 2000

Dyslexia Double Dissociation Dyslexia Subtype ‘LONT’ ‘DEBT’ System Preserved Surface Intact Impaired Phonologic Orthographic Price, 2000

Plasticity and Re-Organization of Language

Definitions Structural plasticity- physiological changes in a given area of the brain in response to learning, injury, or development Functional plasticity- cortical reorganization in response to learning, injury, or development(i.e., the ability of one area of the brain to assume the functional role of another).

Evidence for structural plasticity Mechelli et al., 2004

Language Transfers During, but not After Early Critical Period Speech After Hemispherectomy Age when Lesion Acquired Unaffected or Improved Permanent Aphasia Side of Hemispherectomy Before Teens LEFT 49 3 RIGHT 38 5 Adulthood LEFT 6 25 Basser, 1962 (cited in Lenneberg, 1967)

Transfer of Speech in Left Hemisphere Epilepsy (n=396) Speech Representation Determined by Wada Test (n/%) Age at Injury/Onset TOTAL Left Bilateral Right ≤ 5 years old 134 60 (45) 20 (15) 54 (40) > 5 years old 262 220 (84) 18 (7) 24 (9) Rasmussen & Milner, 1977

When language develops in the right hemisphere - Are language functions supported by the same (homologous), or by different networks? Do some language functions transfer more so than others?

Tivarus, 2012

‘Mirror Image’ Organization after Early Left Injury Differences in Dominant Activation ‘Mirror Image’ Organization after Early Left Injury Areas activated during DN vs. Sound Identification Tivarus, 2012