Chapter 13: Lateralization & Language Flashcards
Rasmussen’s Syndrome
produces seizure in only one hemisphere Hemispherectomy: -Motor control modestly impaired -Language development mostly unaffected -10 point increase in IQ -Recovery of function correlates with age of surgery
The Split Brain
Pathways connecting two hemispheres severed in order to control seizures.
Corpus collosum, Massa intermedia, Thalamus, Anterior commisure and Hippocapmus pathways are disrupted
- No change in personality, intelligence, or speech
- Two separate minds
- Alien hand syndrome
The Split Brain:
Language capacities between two hemispheres
The Interpreter: one hemisphere (usually left) tries to make sense of actions
- Right hemisphere may point to object, but left hemisphere does not know why
- Interpreter attempts to generate a reasonable explanation
Left Hemisphere
logical, language, sequential; verbal
Right Hemisphere
emotional, intuitive; spatial relations
Development of Lateralization
Lateralization is not unique to humans.
May allow organisms to simultaneously attend to different aspects of environment.
Lateralization: Role of prenatal androgens
- Males: higher proportion of left-handers
- Congenital adrenal hyperplasia (CAH): fetus’ adrenal glands release elevated levels of androgens
- Females exposed to twice normal level: no difference in handedness or language laterality
- Males exposed to slightly elevated levels: higher proportion left-handed but no difference in language
Lateralization Factors
- Genes responsible for connectivity between two hemispheres activated at 3-5 months.
- Differential gene expression might result in different wiring patterns, leading to structural and functional differences later in life.
Hemispheric Asymmetry:
Left Handers
10% left-handed
- 70% localize language to left hemisphere
- 15% localize to right hemisphere
- 15% localize to both hemispheres
Hemispheric Asymmetry:
Right Handers
90% right-handed
- 95% localize language to left hemisphere
- 4% localize to right hemisphere
- 1% localize to both hemispheres
Handedness & Language
Dioula tribe: 3.4% left-handed.
Yanomamo tribe: 22.6% left handed.
Dichotic Listening
different sounds presented simultaneously to both ears.
Right handers typically show right ear (left hemisphere) advantage.
Prosody
Prosody = use of intonation and stress in language to convey emotional tone and meaning.
- Left ear, right hemisphere advantage in responding to emotional words.
- Orbitofrontal cortices in both hemispheres respond to conscious evaluation of emotional tone.
Hemispheric Asymmetry:
Musical ability
- Imaging results suggest overlap between language and music
- rTMS suggests right hemispheric activity only
Musical ability:
Perfect pitch
- Planum temporale: brain region near auditory cortex.
- Larger in left hemisphere.
- Twice as large in musicians with perfect pitch.
Hemispheric Asymmetry:
Gender differences
- 3-7 times many boys than girls diagnosed with language disorder.
- Girls begin speaking at younger age, have larger vocabulary, and better reading skills.
- Large meta-analysis found gender difference in lateralization of handedness but not language.
What is a language?
System of rule-based communication that combines symbols (sounds and gestures) in order to express a meaning, idea, or thought.
–Transmit info –Express thoughts and emotions –Automatic, complex, and coordinated –Use of vocalization to communicate –No connection between symbol and what it signifies –Passed from generation to generation –Communication follows social rules –Can communicate about objects and events that are distant in time and place
Origin of Language
Chomsky & Pinker argue for innate ability to learn language.
No specific instruction needed to learn language, suggestive of language module.
Williams syndrome
FOXP2 genes located on chromosome 7
-Modern language acquired 100-400,000 ya due to specific mutation
FOXP2 genes
genes located on chromosome 7.
- KE family: FOXP2 mutation associated with disrupted speech production and comprehension.
- Gene codes transcription factor, which regulates expression of large number of genes.
- Areas in blue functionally or structurally abnormal in KE family.
Schizophrenia
Many symptoms are associated with interpretation and organization of language.
- Generally show no hemispheric asymmetry for language or instead mirror asymmetry, with language lateralized to right hemisphere
- Mixed or ambiguous handedness
- 1% of population throughout world, yet patients have low reproduction rate—must be linked to some positive attribute
Are Nonhumans Animals Capable of Language?
–Communication not the same as language
–Research with great apes
–Mirror neurons
–Broca’s area
Bilingualism
Distinguishing speech sounds: most languages contain 25-40 speech sounds.
Infants younger than ~8 months can distinguish all speech sounds, even those not heard in native language
- /l/ and /r/ differentiated in English but not Japanese
By 11 months, infants can discriminate speech sounds from own language only—supporting idea of critical periods.
Bilingualism: MRI
MRI: second language learning increases grey matter density in certain cortical regions
- Density increases correlate with language proficiency
American Sign Language
Similar language sites activated for spoken written English as ASL; spoken word activation more lateralized.
Wernicke’s area
Word comprehension
Broca’s area
Speech response generation
Speech production
controlled via motor cortex (and Basal Ganglia) activation
Contemporary Language Model
3 interacting language components
Language Implementation System: decodes incoming verbal info and produces appropriate verbal responses—depends on Broca’s area, Wernicke’s area, insular cortex, and basal ganglia
Mediational System: manages communication between implementation and conceptual systems—depends on the temporal, parietal, and frontal lobes.
Conceptual System: manages semantic knowledge—depends on high-level cortical association areas
Aphasias
Brain damage that results in total or partial loss of ability to either produce or comprehend spoken language.
Brain of Dr. Broca’s patient had damage to left inferior frontal region.
While alive, this patient could say only “tan” when questioned.
Conduction Aphasia
• Damage to Arcuate Fasciculus (pathway from Wernicke’s to Broca’s) • Intact comprehension • Can produce fluent speech but often makes errors (can’t correct them) • Problems repeating speech
Conduction aphasia, also called associative aphasia, is a relatively rare form of aphasia. An acquired language disorder, it is characterized by intact auditory comprehension, fluent (yet paraphasic) speech production, but poor speech repetition.
Transcortical Aphasias
TC motor aphasia:
- Dorsolateral PFC damage
- Affects higher cognitive and attentional functions related to language production
- Initiation of speech disrupted
- Unable to produce verbs related to particular nouns
TC sensory aphasia:
- Supplementary motor cortex damage
- Affects ability to understand meaning of words
- Speech is grammatical and fluent
TC motor aphasia:
- Dorsolateral PFC damage
- Affects higher cognitive and attentional functions related to language production
- Initiation of speech disrupted
- Unable to produce verbs related to particular nouns
Alexia
acquired inability to see words or to read, caused by a defect of the brain.
- Word blindness
- Can recognize spoken words
- Left occipital cortex damage affects ability to perceive words and word-like shapes
- Corpus callosum damage prevents transfer of info from right visual cortex to left language areas
Agraphia
- Inability to write
- Damage to motor control areas
- Phonological agraphia: unable to sound out new or difficult words
- Orthographic agraphia: can spell only phonetically
Reading and Writing
Appeared 5-6000 years ago Usually localized to same hemisphere as speech
Dyslexia
Dyslexia: Impairment in reading despite normal intelligence and exposure
–10-30% of population
–High heritability: 40% chance sibling is also dyslexic
–Impaired phonological awareness: ability to discriminate verbal information at level of speech sounds
–Difficulty discriminating rapidly presented stimuli
Visual-Perceptual difficulties: –Reading a word backwards •“net” becomes “ten” –Confusing mirror image letters •“b” becomes “d” –Trouble fixating on printed words •Words appear to move around page
Dyslexia:
Visual-Perceptual difficulties
–Reading a word backwards •“net” becomes “ten” –Confusing mirror image letters •“b” becomes “d” –Trouble fixating on printed words •Words appear to move around page
Stuttering
Producing repetitions or prolonging of sounds.
–Primarily genetic in origin
–Both hemispheres vie to control speech production
–Treatments:
•Reducing rates at which speech is produced and stress associated with the disorder
•Learning special breathing techniques, soft voice onsets, and prolongation of syllables
•Dopamine antagonists
