(BBB) language in the brain Flashcards
week 9
What is language?
Grammar: phonetics, morphology, syntax, semantics.
Ability to articulate something new.
Intention to communicate.
Symbol usage.
Ability to represent real-world situations.
Language may be auditory (spoken), or visual (written or signed)
It involves, auditory system, visual system, motor system, memory.
Disorders of speaking and listening are called?
Aphasia. Caused by stroke, tomour, or head injury.
Dementia
progressive, degenerative brain disorder which can also affect speech and language (e.g. Alzheimer’s disease or frontotemporal dementia)
Broca’s aphasia - symptoms and location of the lesion
discovered in the case of “Tan” who after his death in 1861 an autopsy by Paul Broca revealed a lesion in a region in left frontal lobe which became known as Broca’s area. He could only produce the syllable “tan”. he also had lost use of right arm and hand which is indicative of left side of the brain.
The lesion was in a region in left frontal lobe, became Broca’s area. Broca’s aphasia is associated with damage to Broca’s area (left inferior frontal gyrus only). Results in non-fluent speech, slow, effortful speech production, produce very few function words, but comprehension is unaffected, patients are aware of their deficits and are frustrated by it.
Think of the young girl who struggled to communicate after a stroke.
Wenicke (1874)
case report on 2 patients who
-Relatively fluent speech
-Create new words - ‘neologisms’
-Severely impaired comprehension
Post-mortem of patients revealed lesions in a region in the left posterior temporal lobe which became known as Wernicke’s area.
Patients are generally not aware that they aren’t making sense.
Wernicke’s (fluent, receptive) aphasia
Also affects signers.
Fluent speech, but often content-free
Function words often used approptiately, but many content words (nouns, verbs) missing, some replaced by neologisms (made up non-words)
Severe comprehension deficits.
Generally unaware of their deficit.
Circumlocutions are when someone
talks around or about a specific word as they can’t get it out.
Paraphasias are
a type of language output error commonly assosiated with aphasia
example of phonemic paraphasia
saying ‘pike’ instead of pipe
example of neologistic paraphasia
saying ‘pinwad’ instead of light
(non-words)
example of semantic paraphasia
saying ‘wife’ instead of husband
aka related meaning but incorrect word
example of perseverative paraphasia
previous responses persist and interfere with retrieval/production.
Wernicke-Geschwind model (Geschwind, 1972) building on Wernicke’s findings
Neurobiological bases of language based on studies of brain impairment.
Heard word > Auditory cortex > Wernicke’s ares (decodes sounds for meaning) > Broca’s area (Activates speech plan) > Motor cortex > Speech.
Seen word > Visual cortex > Angular Gyrus > Wernicke’s area (“) > Broca’s area (Grammar) > Motor cortex > Speech.
Arcuate Fasciculus
A portion of a bundle of axons connecting the posterior temporal cortex via the inferior parietal cortex, to locations in the frontal lobe including Broca’s area. Thought to be the route that information travels along between Wernicke’s area and Broca’s area.
Damage or lesions in the arcuate fasciculus results in
inability to repeat spoken language, though fluent speech and good comprehension remain. This is called conduction aphasia.
Word Blindness
Inability to understand written words, lesion to angular gyrus.
Word deafness
Inability to understand spoken words, lesions of fibre tracts from primary auditory cortex to posterior temporal regions.
Global aphasia
The most severe form of aphasia
Can produce few recognizable words if any, and understand little or no spoken language.
Verbal stereotypy - repeat a sound/phrase over and over in an attempt to communicate.
Can no longer read or write.
Preserved intellectual and cognitive capabilities unrelated to language and speech.
Result of damage to the left perisylvian cortex (cortex around the sylvian fissure). Often seen straight after stroke/trauma and can improve but may be permanent.
Apraxia of speech
Non-linguistic speech impairments due to neural injury
Difficulty initiating and executing voluntary movement patterns necessary to produce speech despite normal muscle strength.
Slowed speech, abnormal prosody, distortions of speech sounds.
Specific neural basis unclear.
Comprehension remains fine.
Dysarthria
Non-linguistic speech impairments due to neural injury
Disruption of muscular control due to lesions of either the central or peripheral nervous systems.
Difficult or unclear articulation of speech.
Messages controlling the motor movements for speech is interrupted.
Comprehension remains fine.
Lateralisation
Lateralisation is the tendency for a given psychological function to be served by one hemisphere, with the other hemisphere either incapable or less capable or performing the function.
Is language hemisphere-specific?
Yes, or well the left hemisphere is biased towards language:
The brain is asymetric; the planum temporale (auditory processing and receptive language) is larger on the left in ~ 65% of people. This is present from birth, before speech.
Right ear advantage; if two syllables are played, one to each ear, pp will shadow the right ear (left hemisphere).
Similar right visual field advantage.
Wada technique (Wada & Rasmussen, 1960) - results showed most people, regardless of handedness are LH dominant for language, but when RH dominance occurs, it’s more common in left handed people.
‘Split-brain’ patients (Sperry, 1969)
Some of the strongest evidence for lateralisation.
Present object/word in left visual field > RH > can’t name object
Present object/word in right visual field > LH > can name object
The right hemisphere can compensate: for example (Smith & Sugar, 1975)
Left hemispherectomy on a 5.5 yr old boy to treat epilepsy.
By 26, he had;
Typical language
Typical verbal and non-verbal reasoning
A successful business executive studying part-time for a sociology degree.
Note, RH compensation is a lot less successful for sudden trauma such as stroke.
The right hemisphere is also important for language. How so?
Prosody: use of intonation, emphasis and rythm to convey meaning in speech. (most obvious rh role in language)
Pragmatic language skills: using language appropriately (figurative meaning vs literal, idioms, etc)
LEFT HEMISPHERE
-controls right sided movement
-gets touch information from right side
-auditory information (mainly) from right ear
-visual information from right visual field (not right eye)
-speech (Broca’s aphasia)
RIGHT HEMISPHERE
-controls left sided movement
-gets touch information from left side
-auditory information (mainly) from left ear
-visual information from left visual field (not left eye)
-subtle language (e.g. intonation, metaphor comprehension)
-visuo-spatial attention
