1. Neuroscience: Exploring the Brain, 4e
Chapter 20: Language

2. Introduction Language
System by which sounds, symbols, and gestures are used for communication
Process
Language comes into brain through visual and auditory systems.
Motor system: produces speech, writing
Brain processing between sensory and motor systems; essence of language

3. What Is Language? Language
A system for representing and communicating information
Uses words combined according to grammatical rules
Expressed in a variety of ways including gestures, writing, and speech
Speech
An audible form of communication built on the sounds humans produce

4. Human Sound and Speech Production
Involves coordination of over 100 muscles from those controlling lungs to those of larynx and mouth
All muscles controlled by motor cortex
Air exhaled passes through larynx.
Within larynx are vocal folds.
Sounds produced by vibrations in tightened vocal folds
Sounds modified at further stages of vocal tract
Phonemes: fundamental sounds of a language

5. Language in Animals Human language
Complex, flexible, powerful system for communication
Creative use of words according to rules
Animals do vocalize and use gestures.
Controversial whether their communication is “language”
Do not meet definition of human language: complex, flexible, rules

6. Language Acquisition Mechanisms in infants
Recognize word sounds very early
Statistical learning—combinations of sounds
Syllable emphasis
“Motherese”
Adults talk to infants—speech slower, exaggerated, vowel sounds clearly articulated
Brain mechanisms for language acquisition poorly understood

7. Language Acquisition—(cont.)
Dehaene-Lambertz: fMRI of 3-month-old infant’s brain response to spoken words similar to adults’

8. Genes Involved in Language
Speech and language disorders run in families, more likely to co-occur in identical twins.
Study of KE family generations with verbal dyspraxia
FOXP2 gene single mutation
Affects development of motor cortex, cerebellum, and striatum
Deficits in muscular control of lower face
FOXP2 strongly expressed in brain areas involved in song learning in birds

9. FOXP2 Mutations in the KE family

10. Genetic Factors in Specific Language Impairment and Dyslexia
FOXP2, CNTNAP2, and KIAA0319 mutations
Specific language impairment (SLI)
Developmental delay in mastery of language
Not associated with hearing difficulty or more general developmental delays
Important roles in brain development
Dyslexia: appears to have strong genetic link

11. The Discovery of Specialized Language Areas in the Brain
Aphasia
Partial/complete loss of language abilities following brain damage
Greek/Roman Empires: tongue thought to control speech
Sixteenth century: speech impairment, tongue not affected
1770: Gesner: brain damage
1825: Bouillaud: frontal lobes
1861: Aubertin: cortical area in frontal lobe

12. Broca’s Area and Wernicke’s Area
Broca’s area (1864): region of dominant left frontal lobe, articulate speech
Wernicke’s area (1874): superior surface of temporal lobe between auditory cortex and angular gyrus, lesions disrupt normal speech

13. Wada Procedure
Used to determine hemisphere dominant for speech

14. Broca’s Aphasia Damage in motor association cortex of frontal lobe
Speech is nonfluent, agrammatical.
Difficulty speaking but can understand heard/read language
Paraphasic errors
Pauses to search for words (anomia), repeats “overlearned” things, difficulty repeating words

15. Wernicke’s Aphasia Posterior temporal lobe damage
Fluent speech but poor comprehension
Gardner’s case study
Strange mixture of clarity and gibberish
Correct sounds, incorrect sequence
Speech patterns mirrored in playing music, writing
Area specialized for storing memories of sounds that make up words

16. Wernicke–Geschwind Model
Language processing in the brain
Broca’s area, Wernicke’s area
Arcuate fasciculus
Angular gyrus
Problems with model

17. Parallel Language Pathways

18. Conduction Aphasia
Disconnection lesion of arcuate fasciculus and parietal cortex
In contrast to Broca’s aphasia and Wernicke’s aphasia: comprehension good, speech fluent
Chief deficit: difficulty repeating words
Symptoms: repetition substitutes/omits words, paraphasic errors, cannot repeat function or nonsense words, polysyllabic words

19. Aphasia in Bilinguals and Deaf Person
Aphasia in bilinguals: Language affected depends on order or learning, fluency, recent use of language.
Sign language aphasias analogous to speech aphasias  but can be produced by lesions in slightly different locations.
Verbal and sign language recovered together in one case  indicating overlapping regions used for both.
Evidence suggests some universality to language processing in the brain.

20. Asymmetrical Language Processing in the Cerebral Hemispheres
Split-brain studies
Roger Sperry (1950s)
Split-brain procedure
Sever axons of corpus callosum
Few behavioral effects
Animals behaved as if they had two brains.

21. Split-Brain Humans
Gazzaniga: Brief stimuli delivered only to one hemisphere.
Observations: The two hemispheres initiated conflicting behaviors.

22. Left Hemisphere Language Dominance
Right visual field, left hemisphere language dominance
Left visual field, difficulty verbalizing by right hemisphere in split brain
Image only in left visual field, object in left hand, unable to describe
Unable to describe anything to left of visual fixation point

23. Language Functions of the Right Hemisphere
Functions of right hemisphere: can read and understand numbers, letters, and short words but not with verbal response
Split-brain patient V.J.: right hemisphere able to write but not speak
Right hemisphere: drawing, puzzles, sound nuances
Left hemisphere: language

24. Anatomical Asymmetry and Language
Left lateral (Sylvian) fissure longer and less steep than right
Geschwind and Levitsky: left planum temporal larger than right in 65% cases
Functional human asymmetry: more than 90% humans right- handed
Animals: equal numbers of right- handers and left-handers

25. The Insula

26. Language Studies Using Brain Stimulation and Brain Imaging
Former method: correlate language deficits with postmortem analysis of brain damage
Recent techniques: study language function in living humans with electrical brain stimulation and PET scans
Three main effects of brain stimulation on language
Vocalizations, speech arrest, speech difficulties similar to aphasia

27. Effects of Brain Stimulation on Language
In motor cortex: immediate speech arrest
In Broca’s area: speech arrest from strong stimulation, speech hesitation from weak stimulation
In posterior parietal lobe near Sylvian fissure and in temporal lobe: word confusion and speech arrest
Ojemann studies: in small parts of cortex at different locations: naming, reading, repeating facial movements
Considerable variability in brain areas where electrical stimulation affects language

28. Sites Where Electrical Brain Stimulation Affects Language

29. Effects of Brain Stimulation on Language in Three Patients with Epilepsy

30. Imaging of Language Processing in the Human Brain
fMRI (Lehericy and colleagues): record during three different language tasks
Activated brain areas consistent with temporal and parietal language areas
More activity than expected in nondominant hemisphere

31. PET Imaging of Sensation and Speech

32. Concluding Remarks
Multiple brain areas critical for language, not just Broca’s and Wernicke’s areas
Brain imaging and stimulation studies have revealed widespread brain areas in both hemispheres involved in language.
Language processing involves a collection of interacting subsystems for different language skills.
Many different components: understanding word sounds, meanings of words, grammar, naming objects, producing speech, and more