Week 2 - Language Flashcards
(24 cards)
Localisation of language
Core cortical regions
Anatomical areas
- Broca’s area = inferior frontal gyrus
- Wernicke’s area = superior temporal gyrus
- Surrounding gyri = ventral parts of pre-postcentral gyri, supramarginal gyrus, angular gyrus, medial temporal gyrus
Language areas within the lateral fissure (planum temporale)
Anatomical areas
- Insula
- Hschl’s gyrus (primary auditory cortex)
- STP (superior temporal planes)
Localisation of language
Additional areas
Anatomical areas
- Dorsal premotor area
- Visual areas (reading)
- Parietal cortex
- Cerebellum, thalamus, basal ganglia (coordination).
- Right hemisphere (prosody, contex and discourse)
Localisation of language
Wernicke-Geschwind model
Neural connections betweeen language zones
Classical model of speech comprehension and production
Proposes that comprehension is:
1. Extracted from sounds in wernicke’s area.
2. Passed over the arcuate fasciulus pathway
3. Then goes to broca’s area to be articulated as speech.
Localisation of language
The dual language pathways
Neural connections betweeen language zones
Dorsal pathway:
* Phonological = motor mapping.
* Bottom-up (sounds -> articulation)
* Used for repeating sounds/words
* Damage = impaired repetition and articulation.
Ventral pathway:
* Semantic = meaning mapping.
* Top-down (meaning -> word assignment)
* Used for understanding complex grammar, assigning meanin.
* Damage = can read/produce speech but cannot understand meaning.
Localisation of language
Transcranial magnetic stimulation (TMS)
Speech zones mapped by brain imaging techniques
Why use it, how it works, limitations
Why use it: non-invasive technique to explore language function in healthy individuals.
How it works:
* Produces a “virtual lesion” by disrupting neural function temporarily (effects last from milliseconds to an hour).
* It can interfere with or enahnce reaction times.
* It can be combiend with MRI to target specific regions.
* It can be repeated easily in experimental setups.
Limitations:
* Auditory noise = may induce distractions
* Stimuls passes through scalp and skull = may cause discomfort or contractions.
* Limited access to deep brian structures.
Localisation of language
Key findings
Speech zones mapped by brain imaging techniques
- Auditory and visual word processing occur independently.
- Broca’s area involved in speech production and syntax/verb generation.
- Wernicke’s area handles auditory input decoding and likelymore than just speech comprehension.
- Word meaning appears mapped to object-related areas = visual features in visual regions and motor features in motor areas.
- It reinforces the idea that language is grounded in broader sensory-motor systems.
Localisation of language
Core language network
Neural networks for language
Structure = 5 functional modules, each with a role:
1. High-level language regions (syntax, semantics).
2. Speech perception areas
3. Word-form recognition areas
4. Articulation areas
5. Cognitive control areas
Function:
* Single modules can support simple tasts (ex: speech perception).
* Multiple modules co-activate for complex tasks (ex: discourse)
* Language is supported by modular and dynamic cooperation of specialised subsystems.
Localisation of language
Nodes and neural webs for language
Neural networks for language
Brain constructs “neural webs” to represent words.
A web consists of:
* Nodes = functional units (ex: auditory, motor, visual).
* Edges = pathways connecting nodes.
Each word activates a unique web based on its semantic properties.
Language disorders
History vs modern
Historically = language impairments linked to brain regions like Broca’s and Wernicke’s areas.
Modern = language function is much more complex, involving sensory integration, motor skills, syntax and memory.
Language disorders
Aphasias
Language disorder that affects speech, writing and/or reading, usually due to injury in language-specific brain regions.
Disorders from motor or sensory loss are not aphasias but may co-occur.
Language disorders
Fluent aphasias - general
Fluent aphasias
- Main deficit lies in language input or reception.
- Speech appears fluent and well-articulated but may lack comprehension or meaning.
Language disorders
Wernicke’s (sensory) aphasia
Fluent aphasias
The inability to comprehend or organise words despite fluent speech.
Luria’s 3 characteristics:
1. Sound classification deficit = cannot distinguish nor categorise phonemes and sounds.
2. Speech production deficit = able to speak but confusion on phonetic characteristics which results in WORD SALAD.
3. Writing deficit = unable to write due to phoneme-grapheme disconnection.
Language disorders
Transcortical aphasia (isolation syndrome)
Fluent aphasias
- Repetition is intact, but spontaneous speech and comprehension are impaired.
- May produce meaningful words but lack coherence.
- Word production is normal.
Language disorders
Conduction aphasia
Fluent aphasias
- Can speak, name objects and understand speech.
- Cannot repeat due to disrupted connection between perceptual word image and motor systems.
Language disorders
Anomic aphasia (emnesic aphasia)
Fluent aphasias
- Comprehend speech, produce meaningful speech, and can repeat speech but difficulties in naming objects.
- Struggles specifically with nouns.
- Related to left temporal cortex damage = areas controlling recognition and classification
Language disorders
Broca’s aphasia (expressive aphasia)
Non-fluent aphasias
- Can understand speech but has to labour to produce it.
- The person speaks in short phrases interspersed with pauses, sound errors, repetitious errors and omitting function words.
- The deficit is not in making sounds but from switching from one sound to another.
Language disorders
Transcrotical motor aphasia
Non-fluent aphasias
- Repetition is good but spontaneous production of speech is laboured.
Language disorders
Global apahsia
Non-fluent aphasias
Speech is laboured and comprehension is poor
Language disorders
Alexia, agraphia and word deafness
Pure aphasias
- Alexia = inability to read
- Agraphia = inability to write
- Word deafness = inability to hear or repeat words
Language disorders
Key points about the neural basis of language
Localisation of lesions in aphasia
- Most of the brain participates in language (too complex to be tied to a single, small brian area).
- Most lesion data comes from stroke patients (stroke often affects the middle cerebral artery which supplies core language areas but lesion variability complicates conclusions).
- Symptoms improve over time (initially severe but improves after, making localisation based on early symptoms misleading).
- Aphasia subtypes are varied (they have many symptoms, each possibly linked to distinct neural subtrates).
Language disorders
Cortical language components
Localisation of lesions in aphasia
Non-fluent and fluent aphasias
Non-Fluent aphasias symptoms linked to:
* Apraxia of speech (motor difficulty) = damage to insula
* Sentence comprehension impairment = damage to temporal gyrus.
* Recurring utterances = damage to arcuate fasciculus.
* Articulatory deficits and working memory = damage to frontal cortex.
Fluent aphasias:
* Typically reflects lack of comprehension = damage to temporal lobe and white matter.
* Suggests language also involves occipital, temporal and parietal regions and that temporal cortex-frontal connectiosn are critical
Language disorders
Subcortical language components
Localisation of lesions in aphasia
Thalamus plays a role in language:
* Pulvinar and posterior lateral central complex are involved.
* Important subcortical region
Language disorders
Hemispheric contributions to language
Localisation of lesions in aphasia
Left vs right:
* Left dominates language in most right-handed people.
* Right, althoutl ittle to no speech, contributes more than previously thought = auditory comprehension, some reading ability, recognition of words but little writting ability and understanding of grammar and senstence rules/strucutres.
Right hemisphere can compense if left hemisphere is removed early in life but speech remains limited if removal happens in adulthood.
Conclusion:
* Right hemisphere = language comprehension
* Left hemisphere = language syntax (production, timing, sequencing movements and grammar rules).
