W10: Language

Understand the concept of lateralisation and discuss hemispheric contributions to language

Lateralisation

*Idea that 2 hemispheres of the brain specialise in different functions

^certain abilities are dominant in one hemisphere

Language Lateralisation

• Language is mostly lateralised

• LEFT is dominant for language in 90% of population

- Words

- Grammar

- Speech

• RIGHT dominant in 27% left-handed people and 15% ambidextrous but only 4% right-handed people

Role of the Right Hemisphere

*Comprehension & SPATIAL RELATIONSHIPS

• Damage might affect talking about spatial relations, maps and complex geometrical forms, organising a narrative, understanding figurative aspects of language

- Prosody

- Context

- Emotion

Describe key processes involved in language comprehension

Language Comprehension

• Prosody: intonation and emphasis to convey meaning

• Language also includes more complex, abstract meaning like metaphors 

• Brain works like a dictionary

• Audio and visual entries; we look up words depending on how they look and sound (Wernicke's area)

• Memories associated with words are activated (via posterior language area)

Bilingualism

*Ability to use 2 languages in everyday life

• Majority of people in the world are bilingual or multilingual

• By 12 months infant brain learns to process sounds of language/present in the environment

• Bilingual babies show stronger responses in the PFC

• Potential advantages in attention, task switching inhibitory control

 

Localising bilingualism

Are different languages processed by different brain areas?

- Electrostimulation studies review (Guissani et al, 2007)

- Some overlapping

- Primary or secondary language specific regions

Identify main brain areas involved in language and language problems

Integrated Language Network

• Laterization is not absolute

• Both hemispheres work together connected by the corpus callosum

 

Surgical Cutting of the Corpus Callosum

Split brain surgery…

• Surgical procedure used to stop seizures in severe cases of epilepsy

• Corpus callosum is cut and communication is between hemispheres is disrupted

*In research it helps us understand what each side can/can't do alone

E.g. Input from the left field of view is processed by the right hemisphere and visa versa

- When they showed image in RVF- info went to left & able to name the word

- When they showed image in LVF- info went to right & unable to name but can draw it 

What can split-brain studies teach us about language?

• Evidence that language is lateralised, both localised and distributed

• If information doesn’t reach language areas we may not be able to describe it

• The left hemisphere acts as "interpreter" (builds explanations)

• The right hemisphere knows it- the left hemisphere says it

• The left hemisphere speaks but both hemispheres think

Different types of aphasia: non-fluent

Aphasia

*Language disorders associated with difficulties in understanding and producing language caused by brain damage

^not explained by hearing loss, motor deficit or general intelligence

 

Prevalence & causes

>350,000 people in the UK live with aphasia

35,000 new cases every year in the UK following a stroke

Causes: stroke, brain tumours, head injuries

^significant psychosocial impact

Nearly 60% of people with aphasia experience depression with a year post-stroke

Broca’s Aphasia

Patient Tan…

- Cavity left frontal lobe filled with fluid

- Patient can comprehend but not express speech

- Speech is associated with left hemisphere

- Damage to the inferior left frontal lobe and underlying subcortical white matter

• Comprehension of speech is intact

• Speech is slow, broken, effortful

• Loss of the production of complete sentence structures in speech and writing  

 

Speech deficits in Broca's…

• Agrammatism (loss of grammar)

—> difficulty in use of grammatical constructions but also word order to decode sentences

- "content" words are still used (e.g. nouns, verbs)

- "function" words are more difficult (e.g. a, the, in)

• Broca's Anomia (accessing the word)

—> word-finding difficulties (function words)

• Articulate problems

—> mispronunciations, often alter the sequence of sounds

 

Preserved functions in Broca's…

1. Language comprehension

2. Meaning of words

3. Awareness of deficits

4. Non-verbal communications (gestures/facial expressions)

5. Understanding humour/sarcasm/tone

6. Prosody/expression of emotions

Global Aphasia

*Sever impairment in all language functions

Different types of aphasia: fluent

Wernicke's Aphasia

• Repetitive or fluent aphasia

• Main difficulty is understanding language (spoken or written)

• Speech remains smooth and well-paced but might lack meaning

• Linked with damage in the left temporal gyrus

Pure word deafness…

- Auditory verbal agnosia

- Rare disorder of the recognition of speech

- Patients cannot understand spoken words despite having normal hearing, reading, and writing skills

- Typically caused by disconnection rather than direct destruction of Wernicke's area itself

Transcortical Sensory Aphasia

Poor comprehension but preserved repetition

Speech is fluent, grammatically correct but meaningless 

May not be aware of difficulty

Linked with disconnection between Wernicke's area and posterior language regions

People with TCA may struggle to…

• Understand Y/N questions

• Follow directions

• Understand stories

 

Anomic Aphasia

• Problem with word findings and naming things

• Difficulty retrieved certain words, especially nouns and verbs

• They know what they want to say but can't get the words to come out correctly

• Might use substitution words or related words (e.g. dog or cat)

• Wernicke's area and the broader left posterior temporal and parietal regions involved

 

*Broca's anomia= can't get the word out

*Wernicke's anomia= gets the wrong word out

 

Conduction Aphasia

• Meaningful fluent speech and comprehension, but poor repetition

• Extreme difficulties repeating lists or words (although related words may be repeated)

• May replace word they are asked to repeat with another with the same meaning

• Caused by damage to pathway between Broca and Wernicke area responsible for conveying sound- arcuate fasciculus

• Hearing sentence evokes imagery, which allows individual to describe the meaning but using different words