Language and the brain

LANGUAGE AND THE BRAIN
24.11.2014
BRAIN STRUCTURE AND FUNCTION
Are you left-handed or right-handed?
Left-handers
Right-handers
- Suffer from a variety of language
disorders and learning disabilities
- Die younger
- 10% males, 4% females (US)
- Greater proportion of artists,
musicians and writers
- Dexterity, Latin term for ‘right’
Ambidextrous (Latin: have 2 right hands), Leonardo da Vinci
Handedness is directly related to the structure and development of the brain
Brain + spinal cord = central nervous system (grooved and wrinkled tissue)
Cerebral cortex (cerebrum) /ˈsɛrɪbrəm/
•
Cerebellum /sɛrɪˈbɛləm/
•
Medulla oblongata / meˈdʌlə ˌɒblɒŋˈɡɑːtə/
Pons Varolii
/pɒnz’ vəˈrəʊlɪ/
Cerebellum: a large part at the back of the brain that controls the muscles, movement, and balance
Medulla oblongata: the lowest part of the brain, positioned at the top of the spinal cord, that controls activities such as
heartbeat, blood pressure and breathing
Pons Varolii: a band of nerve fibers linking the medulla oblongata and the cerebellum with the midbrain
Cerebral cortex: the grey outer layer of the cerebrum, responsible for language, thinking, decision, emotion and character
The principle integrator of the
mental processes carried out in
the two hemispheres
Frontal lobe: cognition
Parietal lobe: general somasthetic sensing (in the arms, legs, face etc.)
Temporal lobe: hearing
Occipital lobe: vision
***Structural differences account for intelligence, language and other cognitive functioning. Size and weight do not seem to
play any crucial role.
HEMISPHERIC DOMINANCE
Left hemisphere controls the right side of the body: Right hemisphere controls the left side of the body
- Stroke (affects the body, but not the same way with the hearing and vision)
For right-handed persons, the left hemisphere dominates the right hemisphere
- 40% of left-handers have right-brain dominance, the majority have left-brain dominance –much less
marked than in right-handed persons > result in speaking problems, and reading and writing dysfunctions
Differences between the brains of males (thicker right hemisphere) and females (thicker left hemisphere)
> Injection of hormones can change this state- e.g. female children with high levels of androgen due to
genetic disorder
LATERALISATION
• Left hemisphere: Language, logical and analytical operations and higher mathematics
• Right hemisphere: recognizing emotions, faces and taking in structures globally without analysis
- This separation and function in the hemispheres is referred to as Lateralisation: incoming
experiences are received by the left or right hemisphere depending on the nature of those experiences, be
they speech, faces or sensations of touch
- Associated with lateralization is Earedness! (right handers will hear sounds strongly in the right ear)
nerve fibres: arcuate fasciculus
• - The two hemispheres are not identical – neither structurally, nor functionally
• - Infants at birth have a bulge in the left hemisphere; Wernike’s area is generally larger
• - Sperry: experiment with people suffering from epilepsy, divide the two hemispheres
LANGUAGE AREAS AND FUNCTIONING
- Broca’s area is near that part of the brain which controls speech, Wernike’s area is near the part of
the brain which receives auditory stimuli
- when hearing a word the sound goes from the ear to the auditory area of the temporal lobe to
Wernike’s area – when spoken aloud, the sound must pass to Broca’s area
- Broca’s area is adjacent to the region of the motor cortex which controls the movement of the
muscles
- Some language processes still occur elsewhere in the left hemisphere and in the non-language
hemisphere and may even vary from person to person (e.g. understanding of intonation,
interpretation of emotional intentions, like anger and sarcasm, various social meanings)
BRAIN MATURATION AND CRITICAL AGE FOR LEARNING LANGUAGE
When left hemisphere is damaged then the right hemisphere takes over the reacquisition of language
functions
Lennenberg (experiments with aphasic children): this kind of recovery no longer occurs beyond puberty
Krashen: the age limit of recovery is 5 years
Children are better than adults at acquiring native-speaker pronunciation in a second language (around the
period of puberty there is a decline in motor skills and memory > but there is maturation of the brain)
LANGUAGE DISORDERS - APHASIAS
- Damage in some part of the brain where language is located
(problems in spontaneous speech, understanding of speech and writing)
- Benson, 1967; 2 main aphasias:
Broca’s aphasia
- Broca’s area coordinates speech movements
- 1861, Frenchman Paul Broca: speech disorders caused by tissue damage or destructions in the brain
- Meaningful but shortened speech (telegraphic stage-lack of inflections)
- Speech comprehension is also affected (loss of syntactic knowledge in both speech production and
understanding e.g. a patient could understand: ‘The apple that the boy is eating is red’, but not ‘The girl that
the boy is looking at is tall’.
Wernike’s aphasia
- nonsense speech, double-talk(sounds right and is grammatical but it is meaningless)
- e.g. ‘Before I was in the one here, I was over in the other one. My sister had the department in the other one’
- patients provide substitute words for the proper ones on the basis of similar sounds, associations or other
features. E.g. chair – shair (similar sound), table (association), throne (related meaning), ‘you can sit on’ etc.
- can also cause severe loss of speech understanding
OTHER SPEECH-RELATED APHASIAS
Pure word deafness: (a person cannot recognize the sounds of words as speech)- damage to the area which
leads into Wernike’s area from the auditory cortex
Conduction aphasia: poor ability to repeat words despite good comprehension (e.g. can’t live –ken lee)
Anomic aphasia: problems in finding the proper words for spontaneous speech.
Apraxia: difficulty to perform a skilled motor movement with the hands in response to a verbal command
Global aphasia: many or all aspects of language are severely affected due to massive damage at numerous
sites in the left hemisphere – little speech comprehension and display, usually some stereotypic and
automatic sequences of speech sounds
>>> determination of the type of aphasia depends on the location and the nature of the damage, whether
the tissue was completely destroyed or the damage was slight, whether the damage occurred suddenly or
gradually, when the damage happened.
READING AND WRITING APHASIAS: DYSLEXIAS
After or in the process of acquisition of reading and writing skills
Problems of hemispheric dominance, defects in visual perception – read or write backwards (e.g.
deer as reed)
2 basic categories:
Alexia – disorders in reading (unable to read a phrase but write it as dictationsome cannot read what they have written!)
Agraphia – disorders in writing (total loss of the
ability to write but the hand can be used skillfully for other purposes)
LOCALISM AND HOLISM
- Localist model: model of looking at the structure and function of language by relating specific aspects of
language to certain localized areas of the brain-successful at explaining around 85% of aphasias
- Holistic model: takes into account global brain phenomena
(e.g. distracted while speaking one breaks off and forgets what s/he wanted to say – momentary
damage to Broca’s area; or someone tells you sth. and you don’t catch the words and respond ‘What?’
– momentary break of Wernike’s area)
- 15% of cases do not have damage in those specific areas: e.g. failure to produce grammatical sentences may
not be a result of loss of actual knowledge but a breakdown in the process of constructing sentences
SIGN LANGUAGE APHASIA
- The same general patterns of aphasia emerge in sign as with speech
- Left hemisphere (language), Right hemisphere (spatial tasks) > although right hemisphere is more involved with
the production and comprehension of sign language (space-related phenomenon)- left hemisphere asserts
dominance
- Damage of Broca’s area: uninflected forms (little ability to use a signing space as a grammatical framework to
mark verbs or persons, aspect or morphological changes)
- Damage of Wernike’s area: a patient will produce fluent strings of signs (but meaningless or nonsensical in
sentences)
- Damage to right hemisphere – grammatical and unimpeded sign production; impairment in comprehension of
signs
METHODS OF INVESTIGATING BRAIN AND LANGUAGE
Post-mortem examination of the brains of patients who have displayed lang. disorders (Broca)
• Observing the language of patients who have had brain operations (or war injuries)
• Penfiled, 1950s, electrical stimulation of the cerebral cortex in patients who are conscious during brain
surgery (they remember childhood events or old songs)
• CAT (Computerized Axial Tomography): using X-ray source to make numerous slice scans and integrate them
to a whole by computer, Scientists examined a person, nicknamed “Tau’ and preserved his brain for over 100
years in Paris- his Broca area was affected
• PET (Positron Emission Tomography): direct observation of the brain as a whole, inject a mildly radioactive
substance into the blood and then trace the blood flow patterns within the brain by special detectors which
provide a colour image
--- In 1992, the NY Times reported that, by means of PET:
- the brain distributes language processing over a few or many cerebral areas
- Second languages are rather loosely organized in the brain
(can be localized in the right hemisphere even – Carla: Italian and English)
MIND AND BRAIN
• What is the relationship between mind and brain?
• Is there a perfect correlation between a person’s experiences and the events which take place in
the brain?
• dependence of mental occurrences on the functioning of the brain
• consciousness plays a role in determining events in the mind and hence in the brain?
• Free will vs. determinism
• Are events in the mind wholly determined by other events? / Can a complete understanding of
brain provide a complete understanding of mind?