Lecture 7: Language Flashcards
Language is a network of many aspects, name some
- comprehension
- speech
- writing
- reading
- musicality
Involves many non-language-specific (but necessary) brain areas: motor functions,
vision, auditory processing, working memory…
What is meant by the left hemisphere dominance?
Language in mostt individuals is lateralized in the left hemisphere (for right handed individuals).
Brain areas involved in language
Language never works in isolation, and all these regions are connected through white mattter tracts.
Inferior frontal gyrus (IFG)
- Broca’s area (BA 44/45) is here (Broca’s area is a general term -> area that broca discovered)
- Area 44 & 45
- Very important for the production of language! (when there is a lesion in it = issues with language).
Inferior Frontal Region
- Broca, with his patient Leborgne, was the first to say that the frontal lobe was critical for language. His patients Leborgne demonstrated a clear association between stroke in IFG and speech production.
- Broca also studies another patient: Lelong
- Could only use a few words
- Also had a lesion in the IFG (like Leborgne)
- When Broca first studied these patients he considered that their language comprehension was intact
- But, now we know that the lesions in those two patients were extending in adjacent
areas (not specific to the inferior frontal region –> involved more than the IFG) - NO clear evidence that specific damage to “Broca’s area” would cause the same language production deficits –> most likely lesions in just Broca’s area would not cause as brutal effect.
Other regions for speech production
1) The anterior Insula (left):
- Critical for coordination of speech articulation
- Part of the orofacial motor system (connection with motor area of the mouth)
2) Precentral region (of insula):
Orafacial musculature control ->movement of face + mouth
3) Basal ganglia
- Cognitive control (enhancement and suppression, initiation of the different steps required in language production)
- Supports the selection of appropriate phonological and articulatory representations of the lexical items needed for speech.
- People who stutter often have differences in basal ganglia
4) Cerebellum
- Important for motor planning and control
Electrical stimulation
- Had an important role in establishing the core language regions of the brain
- Used for neurosurgical operations
- The patients were awake (only local anaesthesia used)
- Surgeries were done in order to guide the limits of the surgical excision
- Stimulate brain areas and see how it interferes with speech (surgeons did not want to affect language areas)
- Ex. Ask the patient to count, name pictures or objects or to just be silent.
Sometimes electrical stimulation elicits/induces vocalisation:
- A silent patient (stimulate the ventral part of area 6 = produce vocalisation, area responsible for motor aspects of sounds).
- If you stimulate the appropriate precentral gyrus it may induce a vocal response, like a sustained sound (not language)
- Orofacial region
Sometimes electrical stimulation causes a disruption of speech:
-ask the patient to produce speech
- Stimulation of the ventral precentral regions and supplementary motor region
- Causes interference with the motor production of words
- Interference with speech can also be induced by language specific areas
- Either speech arrest or hesitation, word distortion, incorrect naming, etc.
- Stimulate motor area = interfere with speech. Different areas created different changes.
Dr Penfield
Red = Stimulating Precentral areas: evokes sounds of vocalization (area 6 responsible for orofacial area).
Blue = Stimulating area 44: speech arrest (could not produce speech anymore)
Conclusion: must be the region sending the commands to area 6 to open and close the mouth the right way.
Area 44
Pars Opercularis
- Intermediate between the cognitive retrieval (area 45) and motor/articulatory (area 6) –> area 44 is the area betwen area 45 and area 6.
- Able to translate the information that is retrieved by area 45 (ie: retrieving the right word) into action (motor output of area 6).
- Strong connections to the Supramarginal gyrus (phonological processing). Area 44 connest the supramarginal gyrus with the SFL III.
Area 45
Pars Triangularis
- Involved in active retrieval of information before it can be articulated (ie what word do I want to choose)
- It has a strong connection with comprehension/semantics processing areas of th temporal lobe
- Strong connections with other frontal areas.
- Strong connections with the angular gyrus (semantics processing) semantics = chronological information
- integration and selective retrieval of
information
Basically area 45 retrives information then gives it to area 6 to say it.
Penfield continued
Noted that electrical stimulation in any of the core language areas of the brain will affect
speech
Peri-Sylvian areas:
- first described by doctor penfield
- close to sylvia fissure
- language relies on a network.
Posterior Temporal Regions
Another very important region for language!!
- Carl Wernicke (1848-1905) was the first to show the importance of this region for auditory language comprehension (critical region). –>The superior temporal gyrus
- Now when we consider Wernicke’s area, we don’t only consider that it is on the superior temporal gyrus but that it extends to the superior temporal sulcus and also part of the
middle temporal gyrus.
*The posterior temporal region starts in the sylvian fissure
Comprehension of language in the posterior temporal region (1)
- Acoustic-phonological analysis of the speech input
Heschl’s gyrus, primary auditory cortex (area 41, 42)
* superior surface of the temporal lobe is involved in the processing of any type of sound
* processing of acoustic properties.
Posterior Superior temporal gyrus (STG) and sulcus (STS), (area 22) make up the
secondary auditory cortex
- This part of the temporal lobe responds to acoustic feature of phonetic parameters
- This is where we are able to differentiate speech from non-speech.
Comprehension of language in the posterior temporal region (2)
2) Syntactic and semantic processing:
**MTG and pSTG/STS **
(more towards anterior lobe = understand complex language)
- comprehension of words
- semantics,grammatical aspects
aSTG:
- processing syntatic structure (ex: not activated when just a list of words), but also for semantic processing. More active for processing complex meaning of sentences
more info
- MTG (middle temporal gyrus): involved in the comprehension of words
- STG and STS have different roles depending on where they are located (i.e., anterior vs. posterior)
- Posterior STG and STS –> involved in semantics and grammatical aspects of language
- Anterior STG -> involved in processing syntactic structure (ex. not activated when there is just a list of words), and for semantic processing
Sentence Processing
There is a somatosensory aspect to it, analyzing the structure, word processing aspect, processing grammar, etc. (cannot be done by one
region).
- You need a network of brain regions connected together to do this very complex task.
You need to process:
1. Acoustic-phonological analysis (primary auditory areas)
2. Sentence-level processing: local phrase is built on the basis of word
categories
3. Syntactic and semantic relations in the sentence = interpretation and
comprehension
Inferior parietal areas
Also plays an important role in language.
Studies by Joseph Jules Dejerine in 1891
- Dejernine’s patients with lesions of the Angular gyrus: impaired reading and writing
- Were able to show the role of the inferior parietal lobule (IPL) in reading and writing.
- IPL: composed of the supramarginal gyrus and the angular gyrus (located posterior to it)
- This area, when we talk about language, is often referred to as Geschwind’s territory
because of his work on the IPL in language.
IPL
Geschwind theorized that the language areas are connected to sensory modalities (audition, vision, somatosensory) through the angular gyrus.
IPL = integration of visual, somatosensory and auditory.
Recent Neuroimaging studies:
Involvement of the IPL in reading and semantic processing (Angular gyrus)
Supramarginal gyrus: involved in phonological processing (sounds, work with area 44 for production).
Connections within the language network: How the different brain areas in language are anatomically connected into functional networks
Language network is formed by the inferior frontal areas and the posterior central areas
There are different types of anatomical connections:
- Short range (e.g., within the IFG, area 44 with area 45)
- Long range (e.g., connecting temporal to frontal language areas)
Dual stream model –> says there are two pathways involved in language:
1. The ventral pathway: support sound-to-meaning mapping
2. The dorsal pathway: support auditory-motor integration
Dorsal pathway:
- posterior temporal with frontal
- arcuate with frontal lobe
- occipital +temporal
The Arcuate Fasciculus (AF)
- The classic language pathway (language comprehension with language production).
- A very large bundle of axons that link the posterior temporal language region with the ventrolateral frontal areas, arching around the posterior end of the lateral fissure.
- The AF connects the posterior temporal region involved in the comprehension of
language (often referred to as Wernicke’s area) with the inferior frontal gyrus (IFG)
where Broca’s area lies, the key region for language production - Lesions of the fibres of the left AF disconnecting the posterior temporal language region from the IFG are considered to result in conduction aphasia.
- Why? What you heard doesn’t get conveyed to the language output area. You can produce speech but can’t repeat it (missing link between what you hear).
- Conduction aphasia = Impairment in the repetition of speech
Two branches of the AF
The description of the AF was made possible through dissection, resting-state studies, and diffusion imaging tractography
Two branches of the AF:
- Ventral branch: connecting the IFG
- Dorsal branch: connecting more dorsal regions of the frontal lobe (ex. MFG area 8),
which is very important for attentional control –> auditory frontal attention
- But another way, this branch (dorsal) connects the posterior temporal region (Wernicke’s) for language comprehension with regions like area 8 in the frontal lobe for auditory attention
The Superior Longitudinal Fasciculus (SLF)
When we talk about the SLF, in general, we are talking about parieto-frontal connections.
- 3 major branches:
- SLF 1: links the superior parietal lobule with caudal dorsolateral and dorsomedial frontal regions (not involved in language).
- SLF II: links the caudal part of the IPL (Angular gyrus) with the lateral frontal areas, including area 45
- SLF III: links the rostral part of the IPL (Supramarginal gyrus) with lateral frontal areas (including area 6 ventral and 44)
SFL III
Stronger connections to area 44.
We know this from:
- Precise macaque monkey
invasive anatomical studies
- Resting-state in humans
- Connections of the Supramarginal
gyrus with Broca creates an articulatory loop. - Involved in phonological processing
Exists in both hemispheres
Sending correct information to word correctly.
SLF II
- Stronger connections with area 45, so this track is really important for verbal retrieval.
- Connections with Angular gyrus:
semantic processing and reading - Involved in semantic processing and with verbal retrieval
The Temporo-Frontal Extreme Capsule Fasciculus
- Connects the ventrolateral frontal region with the intermediate part of the supero-lateral temporal region: associated with the long-term storage of semantic information.
- Runs under the insula
- Ventral stream of language
- Associated with the controlled retrieval and selection among competing semantic representations (stored in the temporal lobe).
Posterior temporal area to frontal area
Frontal lobe connections to the temporal lobe
Can globally divide the temporal lobe into three sections:
a. The most posterior temporal sections are connected to the frontal areas by the Arcuate Fasciculus (AF)
b. The intermediate section is connected by the extreme capsule fasciculus (FTexcF)
c. The anterior part of the temporal lobe is connected to the frontal region by the Uncinate fasciculus
Dorsal and Ventral streams
Dorsal and ventral streams (paper by Saur et al. 2008)
- Study supports the dual stream model of language
- Researchers combined fMRI and diffusion MRI (dMRI) tractography
For the fMRI task:
* Presented words and sentences in an auditory fashion.
* Participants had to repeat the sentences.
* They used real words and pseudo words (appear to be real words)
Result:
* When the participants were REPATING the words, the superior temporal and premotor regions of the brain were activated, and they interacted via a dorsal pathway along the AF/SLF.
Comprehension task where the participants listened to normal
sentences compared to meaningless pseudo sentences.
* The areas activated during this auditory comprehension task were the middle and inferior temporal regions and the ventrolateral prefrontal cortex, interact via a ventral pathway that runs through the TFexcF.
Conclusion:
* AF was useful to map the phonemic representations of the
words onto motor representations for articulation, thereby constraining the planned motor output with the mental representations of the sound structure.
- In contrast, the TFexcF was found to be useful for monitoring processes during repetition.
The TFexcF:
- Connects the intermediate temporal areas involved in lexical and semantic processing.
- Helps in deriving meaning from the words
- So, the AF may be useful for repetition alone but if you want to derive meaning the TFexcF is where it’s at
- Both networks interact closely for efficient verbal communication.
Language regions and language tracts
LANGUAGE REGIONS
Comprehension of spoken language:
A1 → posterior temporal areas → more anterior temporal areas
Produce speech:
IFG + Area 44 + area 6 + insula…
Area 45
LANGUAGE TRACTS (white matter tracts)
Arcuate Fasciculus:
Posterior temporal areas → IFG (repetition)
SLF: IPL to IFG
- SLF II: 45 to Angular (verbal retrieval and reading)
- SLF III: 44 to SMG (articulatory loop)
TFexcF: Intermediate temporal areas to IFG (map sound-to-meaning)
Which part of the brain is associated with which function?
Inferior Parietal Lobule (IPL): reading, writing
**Broca’s Area: **Speech Production
Angular Gyrus: Reading and writing (the angular gyrus is part of the IPL)
Arcuate Fasciculus: speech repetition/ sentence repitition (white matter tract that links broca’s area with the posterior temporal areas)
Auditory Cortex: Processing Sounds (not language in general, any kind of sounds
Insula: Articulation
Posterior Temporal area: Language comprehension
