Language
Neuroscience of language
Aphasia lanugea disorder resulting from brain damage (eg stroke, cerebral haemorrhage, TBI,brai tumors ,encephalitis,meningitis
Nuero imaging -fmri pet,DTI
Nuenrophysilogy EEG,MEG
Broca's Aphasia
1.Speech is effortful hesitant contains long pauses and is very non-fluent.
2.Virtually no grammatical structure no sentences and few or no function words prefixes or suffixes
3.The comprehension of speech, at least for single words and simple sentences is often very good.
Wernnickes Aphasia
Speech is effortless fluid and rapid generally grammatically correct with many functions, words, prefixes and suffixes.
The content of words that are produced is rarely words with specific meaning.
Comprehension of speech is severely impaired sometimes even single spoke words cannot be understood even though they are correctly percieved.
Double dissociation- Brain injured people can show dissociation between understanding words and producing words
Wernicke Lichtheim Model (1885)
Patient can comprehend but cannot produce normal speech
Patients can produce fluent speech but have comprehension difficulties.
Conduction Aphasia
Patients can comprehend and produce language normally but cannto produce nonsense words
Pure word deafness
Patients can comprehend environmental sounds but into speech sounds. Written comprehension is good.
Limits of Classification
Few pure cases (receptive and expressive problesm co-exist)
Broca Aphasia revisited
Showed damage well beyond Brocas area,
All damaged patients with Brocas aphasia had damaged insulae.
lesions also affected multiple white matter tracks
Subdividing brocas area- different pattern of receptors
Pars Triangularis Ba45 - connects via direct doral route ,Semantic processing difficulties
Pars opecularis Ba44- connects tot the temporal lobe via arcuate fascicles, Syntactic processing difficulties
Functions Brocas area
Function of the Broca's area
Patients with lesions affecting Broca's area was impaired only for sentences that involved syntactic movement.
Both conditions involve the same syntactic contrast, Broca's area only shows an effect when syntactic roles are semantically unconstrainted.
Increased activation for garden path sentences- initial meaning turns out to be incorrect
Increase activation during speech production task (word retrieval and articulation)
Broca's area supports sentence processing via a more general role in resolving conflicts between competing representations.
-Syntactically complex sentence
-Ambiguous sentences
-picture naming
Revisited
Meta-analysis of fMRI studies of auditory linguistic processing, posterior to anterior shifts as stimulus length increases.
Phonemoe length- Behh, ahh , tt
Word-length (identifying word)
Phrase-length
Auditory words from areas analogous to visual word form area in antieror superior temporal gurys.
Large expanse and temporal and parietal lobe
Disconnection between brocas and wernickes areas
Conduction aphasia revisited- in wernicke-Lichtheim mode, conduction aphasia attributed to damaged to arcuate fasciculus.However, the diffusor tensor imaging shows a complex network of white matter tracts throughout the perisylvian region. Through various areas.
Conduction aphasia- shown through lesion overlap approach that the SPT- most posterior part of theplanum temporale in conduction aphasia is always effected. The SPT forms part of the sensory-motor integration circuit for vocal tract
Debate on where the wernicke area is
Dual stream model
Dorsal stream-mapping from sound to speech output
Ventral stream-mapping sounds to meaning
FMRI changes in the bold signal blood measuring changes of blood oxygen in the brain. If it is more active then it's using up more oxygen.Blood oxygen level dependent response.
Which part of the brain is activated whilst listening to these sentence. Doesn't tell how the brain is processing the beginning of this word vs the end of of this word.
Analysing data from FMRI and MEG etc
Event related potentials (EEG) , Event related field (MEG)
EEG has poor spatial resolution but decent temporal resolitoin
MEG- Fluid keep sensors to zero,
Brain resopnse to individual stimuli are extremely noisy.
Averaging together responses to lots of stimuli means the noise cancels out. Whilst the stimuli that is always present is increased.
N400 is sensitive to ...
N400 is also affected by the predictability as well as congruence of the word. eg Don't touch the wet paint or dog .
Reduced N400 for semantically primed words . Table-chair, hook -look
N400 affected by word frequency
N400- Increased negativity at 400ms for incongruent words dotted lines. Eg one card with He, spread socks. When the word does not make sense.
Is affected by real world knowledge eg the actual colour of trains The sdyney train colours are bliue
N400 signifieis
Orthogrpahic- mapping written nature of the word phonolgical analysis -identifying words form the sound
Semantic memory acess- from word to memory
Semantic/conceptual unification
The transition from unimodal to multimodal representation Kutas, Sound or written form, Multimodal representation connects as modes of the words from sound to written.
Localising the N400 - superior temporal gyrus, anteiror temporal lobe, Brocchas area
p600 -syntatic violations elicits a p600 response
Have a posterior distribution
P600 also affected by syntactic complexity but with a more frontal distribution
P600 thought to reflect two distinct processes-repair (incorrect vs correct structure)and reanalysis (complex vs simple strucutre)
Early Left anterior negativity -studies report an earlier response to syntactic violations at left frontal electrodes
MEG studies localise the ELAN to left anterior superior temporal lobe .
Next challenge is to integrate the temporal and spatial models of the language in the brain