Lecture 8: Language Disorders Flashcards
Aphasias
Main one: Disorders of language resulting from brain damage.
- Historically, there are two types of aphasias: language and speech
- Speech aphasia: verbal output is impaired, because articulation muscles are
weak or uncoordinated (associated with motor production of language.
- Language aphasia: verbal output is linguistically incorrect (linguistic aspect of output).
- Now know there is an aphasia more associated with comprehension.
- Can also observe deficits in comprehension of spoken or written language (normal hearing and vision)
- Other intellectual abilities are “normal” –> cannot be associated with any other impairment like auditory, intelectual…
- Aphasia was one of the first demonstrations that selective brain damage can affect one specific behaviour and spare others = The origin of the field to study brain-behaviour relationships (Broca).
Paul Broca
Paul Broca 1861
- associated his lesion to the language production deficit and named it Broca’s Aphasia (aka non-fluent aphasia). People with Broca’s aphasia are non-fluent in their speech production.
- Was the first person to demonstrate that aphasia was linked to specific lesions
- Lesions primarily in the left hemisphere. This is how they started to understand that language was lateralized in the left hemisphere for most people.
- It is now clear that a very specific lesion to Broca’s area does not cause major aphasic
problems like he originally described
- There is only a milder language production problem
Dronkers reading:
It’s clear now that very specific lesion to broca’s area alone is not essential to produce those kind of very severe brocas aphasia deficits like described with the labogue and patients of Broca. Those patients more was affected, even the white matter leading to Broca’s area what affected.
Carl Wernicke 1874
In his studies he was able to show that damage to the frontal lobe (Broca’s area -> superior posterior temporal area) vs. damage to the temporal lobe (Wernicke’s area) cause different types of aphasias
Broca’s Aphasia
- Expressive ( or nonfluent) aphasia
- Reduced speech production
- Slow speech, effortful (seems hard), not fluent
- Poor articulation
- Fails to produce correct English sentences (gramatically and linguistically correct sentence)
–> Only basic words and endings can be omitted
–> Aggrammatism: no grammatical structure, problems with syntax - Similar deficits with writing (writing is also a motor output language)
Preserved:
- Single word findings (still find words)
- Language (spoken and written) comprehension is intact
- Musical capacities are intact (associated with right hemisphere)
- Sometimes patients also have paralysis on the right side of the body –> if the lesion affects the motor areas (motor/premotor cortex - extends to the arm…)
Wernicke’s Aphasia
(aka language aphasia) –> opposite to brocas aphasia
- also called Receptive aphasia
* Lesions are in the temporal areas of the left hemisphere (temporal areas are very far from motor area = no motor area usually affected.
- No paralysis
- Speech output speed is not affected and can even be more rapid than normal
- Effortless speech
- Normal prosody, rhythm, and melody of speech (intact - produce what seems like normal language)
Deficits:
- Speech is empty, conveys little information, and patients use neologisms (made up words). No meaning to their speech.
- Can also observe Paraphasia: error in word usage. They most often have verbal paraphasia (meaning of output is effected).
- Phonemic paraphasia: replace a single sound –> ex. “spoot” instead of “spoon”
- Verbal paraphasia: whole word is replaced –> ex. “fork” instead of “spoon”
- Example sentence: “I was over in the other one, and then after they had been in
the department, I was in this one”
- Different from Broca’s aphasia –> output is really flowing.
- Overall, it is a profound failure to understand/comprehend language (spoken or written) —> patients have no vision or hearing impairment
- People with this type of aphasia also lose the semantic meaning of words (i.e., the sound patterns is received in the primary auditory area but the high level analysis of the sound is not there).
- More difficult to live with than Broca’s aphasia
Wernicke’s Theory
Broca’s Area
* Concluded that because Broca’s area is located right in front of the motor area for the face, tongue, lips, and vocal cords –> this area must contain the rules and code for articulation of speech.
Wernicke’s Area
- Whereas, Wernicke’s area is located next to the hearing area
- So this area must be involved in the recognition of the patterns of spoken
language
- From his research, Wernicke deduced that these two areas must be connected!
Conduction Aphasia
- Fluent speech but paraphasic(jumbled) speech and writing.
- Comprehension is intact
- Deficits are mostly in sentence repetition
- Naming difficulties
- There is a disconnect between Wernicke’s and Broca’s area
- So, the damage is to the Arcuate fasciculus (white matter).
That is why it is called conduction aphasia –> because it is damage to the fibres that conduct the information between the language production and comprehension areas
- But both Broca’s and Wernicke’s areas are intact
- There is fluent speech and normal comprehension.
Usually this type of aphasia is due to lesions in the inferior parietal lobe near (underneath) the supramarginal gyrus
- If you ask someone with this aphasia a question, they will respond so there is speech comprehension.
- BUT, if you ask them to repeat a sentence they may be able to repeat a simple one but the harder the sentence, the more intense the deficit
Experiments related to paraphasia
Weiler and colleagues: 100 aphasic patients
Wanted to test the patients on ability to map sound to articulation.
* Found two types of patients with paraphasia:
1) Parietal lesion (around the supramarginal gyrus): Lesion in parietal lobe, mostly white matter. → speech is not perfect: paraphasias, concluded that paraphasias (ex : substituting one letter for another) is a problem of disconnection. (Phonemic Paraphasia)
2) Damage to the anterior and intermediate temporal areas: sound-to-meaning problems, difficulties with semantic interpretation of what is being said (verbal/ semantic Paraphasia)
→Phonemic paraphasia: replace a single sound.. Ex: ‘’spoot’’ instead of ‘’spoon’’. Type of paraphasia associated with conduction aphasia so affecting the AF.
→ Verbal (semantic) paraphasia: replace a whole word Ex: fork instead of spoon
→Dorsal stream damage versus ventral stream damage. Different damage depending on which stream is impacted.
(Duffau et al. 2005)
Electrostimulation in TFexcF white matter : semantic paraphasias (i.e. substitution of a target word by semantically related word, such as cat → dog)
Julie’s Case
- Unable to name things she sees, but she can clearly describe them, she knows what they are and she can understand what is being said to her (i.e., she cannot translate visual and semantic info to speech)
- Really a problem translating visual information to speech.
- She can generate a lot of speech that sounds very fluent.
- **The lesion is in the parietal lobe –> translating visual information into speech or translating the auditory information into speech. **
- Lesion probably extended to the AF which would explain her inability to repeat.
- Even when the researcher told her the answer, she was unable to repeat it
- Also affected the white matter tract under this area!
- Parietal lobe plays an important role in retrieving phonologies associated with words
- Good example of a lesion in the dorsal pathway
Remember:
- Ventral pathway: support sound-to-meaning mapping
- Dorsal pathway: support auditory-motor integration
Apraxia of speech
- Impairments in the coordination and planning of speech movements, articulation (coordination and planning of the motor output of speech is affected).
- Making articulatory errors
- Intact: ability to perceive speech sounds
- Lesion in the Insula: the left precentral gyrus part
Dronkers 1966 - study that showed importance of insula in speech production.
25 stroke patients with apraxia of speech
- Patient’s brains were scanned to find the common lesion site.
- In this study, they were surprised to see that the overlap of where the lesion was
not in any language region known at the time –> it was in the insula
- From this, they concluded that the insula played an important role in articulatory
planning
- More specifically, the precentral gyrus part of the insula
Isolation of the speech areas
- Usually caused by carbon monoxide poisioning (quite rare).
- This syndrome is not caused by specific localized lesions in the brain, but, because of
carbon monoxide poisoning it isolates speech areas from the rest of the brain (mostly affects white matter). - No language comprehension
- No spontaneous speech production
- Can repeat perfectly (opposite of conduction aphasia)
- Can even complete a sentence
- Peri-sylvian language areas are spared but disconnected from the rest of the brain (cortical areas of the left hemisphere intact and connected together)
- How could they still finish a sentence?
- Hippocampus was intact!
- This syndrome stresses the fact that the whole network is important for language
- This syndrome is the opposite of conduction aphasia
- Person can do everything but repeat
- Here, they can’t do anything but repeat
The right hemisphere
Lesions in the right hemisphere can also affect language. Left hemisphere is dominant for language but right hemisphere is still involved.
Possible problems:
Usually issues with the musicality of speech because the right hemisphere is the one that is specialized in music. Right hemisphere = music perception
- Prosody, or cadence and intonation of speech, and pragmatics
- Sound flat in their intonation
- May fail to comprehend emotional nuances, irony, sarcasm, and humor in the
speech of others –> they understand what is said but not HOW it is said
- Right hemisphere is involved in music perception
Lateralization of language functions
Some patients have damages to the right hemisphere and display language problems → most are left-handed
The Amytal Sodium or Wada test:
- Mostly used before surgery to see which side of the brain controls language
- Injection in blood into the right or left internal carotid artery to anesthetize only one hemisphere at the time.
- Effect lasts about 10 minutes
- During this 10 minutes they would look at the patient to see if language was affected or not to know which side of their brain controls language.
- Handedness is a continuous variable (you get a score between +100, which is completely right handed, and -100, which is completely left handed)
- Language in the right hemisphere could be up to 27% in strong left-handers (handedness = -100)
Changes in lateralization with age
Changes in lateralization with age (paper presented in lecture)
Depends on the age of the patient
1. In very young children, damage to either hemisphere can result in language deficits. Young children usually have better recovery.
2. Language can be recovered in many young patients even if the left hemisphere is
severely damaged
- As the brain develops, language becomes more lateralized in the left hemisphere!
- If there is a lesion in the left hemisphere (in an 8 year old), the right hemisphere can still
compensate for some language processes
Dyslexia
- Difficulties in the acquisition of literacy
- Developmental dyslexia can be due to different reasons
A PET study of Dyslexic versus Controls
- Both groups show activity in reading-related areas (precentral, articulation areas, temporal auditory areas and visual occipital areas)
- Group difference
Dyslexics: less activation in area 44/6 (articulation) and in ventral occipito-temporal areas (important area for reading).
Remember:
dylexia = developmental disorder
alexia = acquired disorder after lesion
Alexia and Agraphia
First described by Dejerine (1892) → first to identify that the inferior parietal areas play a role in reading and writing.
Reading problem = Alexia
Writing problem = Agraphia
Patient 1 → Alexia with Agraphia
- Patient lost the ability to read and write
- But the patient had good vision
- No aphasia
- The lesion of this patient was in the left angular gyrus
Patient 2 → Pure Alexia without Agraphia
- Right visual field defect
- Lost the ability to read
- Could still write but could not read what he wrote
- Lesion was in the left visual cortex + posterior portion of the corpus callosum
- Explains why he could not see
- Dejernine’s explanation: Written language could only reach the right hemisphere and it was impossible to transfer the information to the left-language comprehension hemisphere due to the lesion in the posterior part of the corpus callosum
Dejernine’s Conclusion:
Concluded that the occipito-parietal areas specialized in visual aspects of language. If you prevent the occipital input to go to the left parietal lobe then you will have reading deficits.
How does it work when you “see” language?
* Retina → striate cortex → secondary visual area → angular gyrus (where visual information is represented in space)
- Visual information is also sent to Wernicke’s area, and Broca’s if you want to read
aloud
- How do you “hear” language?
- The information goes to your ears →primary auditory area →Wernicke’s area
Lesisons of the VWFA
- Also causes pure alexia. VWFA is a an essential step to process written language (letterbox for language). Lesion in VWFA causes pure alexia even if occipital cortex and right side of brain is intact, cannot proccess and ssent it to wernicke or angular gyrus.)
- Why the VWFA?
- This part of the cortex possesses prior properties making it appropriate for reading. Located on fusiform gyrus. Ventral stream of vision.
- Has a preference for high-resolution shapes
- Sensitivity for line configurations (useful for object recognition)
- Location: proximity and connections to spoken language areas (wernicke’s area).
Stanislas Dehaene
Did a fMRI study with kids who were non-readers (6 yrs.), kids who were readers (6 yrs.) and older kids who were readers (9 yrs.)
- Proposed the neuronal recycling hypothesis: visual word recognition is a result of recycling cortical structures whose initial functions were for object recognition (brain area is already there and responsible for decoding the different shapes. As kids learn how to read = more activation in the VWFA).
- Conclusion: as you acquire expertise, this specific area of the fusiform gyrus becomes more active and more specialized for words
- Different aspects of language are not exclusively associated with the function of one brain area
Agraphia
- Central agraphia (also called “linguistic” or “aphasic“ agraphia): language aspect of writing is affected
- Peripheral agraphia (also called “nonlinguistic” or “nonaphasic” agraphia): motor output is affected.
- Writing requires to have:
1) the knowledge of the set of coordinated movements to correctly draw out letters (praxis) = which movements you need to create.
2) the ability to “mentally queue up” a sequence of letters to make an entire word (motor programming)
3) the visuospatial ability to guide a writing implement on a writing surface
4) the motor system to carry out these tasks.
Latter steps involved in the motor planning or motor action of writing leads to peripheral
agraphia
Central Agraphia
Central Agraphia
* IPL lesions: conversion of verbal representation of language to visual
representation (mostly angular gyruss)
* May be further subdivided into subtypes:
-Phonological agraphia: disproportionate difficulty with the writing of
nonwords (e.g., flig, merber) compared with real words
-Lexical agraphia: marked impairment writing words with irregular sound–
letter correspondences (spelling how words sound)
* Frontal lesions: central agraphia with grapheme substitution, semantic errors,
intrusions, substitution
Peripheral agraphia
Peripheral agraphia
(areas after the language processing area, guide motor actions to write)
SPL lesions: letter formation, spatial organisation, letter omission or addition
* Apraxic agraphia: organization of the writing on the paper in the space will be affected - spatial.
→isolated impairment in written language
→intact verbal language and reading ability.
→ writing impairment stems from disruption to processes involved in the motor planning and output of writing, downstream of linguistic processes.
SMA (supplemental motor area) lesions: hesitation trembling, approximations
Motor Agraphia:
Motor agraphia is broad and occurs due to the disruption of the motor system downstream of praxis, anywhere from the motor cortex to the peripheral nerve and muscle.
