language Flashcards
Broca’s aphasia 1861
Broca 1861
observed aphasia marked by speech that is
arduous, non-fluent, telegraphic, few-closed class words, word-finding pauses and agrammatic
comprehension on the other hand is relatively preserved
postmortem implicated BA 44, 45 in the left inferior frontal gyrus near the motor cortex used in speech
Wernicke’s aphasia 1874
aphasic patients who presented with fluent speech, lacked meaning, neologisms, paraphasias, anosognosia
associated with BA22 in the left superior temporal lobe
what is aphasia
the specific loss of language
deficits can be global, mixed or unitary (in production, comprehension, repetition, syntax, semantics, phonemes) depending on the level(s) of processing that are disrupted
How do patient studies inform the location of function
many different pathologies which can affect the same areas and produce the same language impairments (stroke, tumour, surgery, atrophy)
however deficits change over time (spontaneous recovery, compensatory strategies)
diaschesis (white matter changes can affect distal areas)
strokes correspond to vascular boundaries rather than functional ones
rather than localised function, the double dissociations between aphasia presentations inform processes underlying language
what is the evidence that there are comprehension problems in Broca’s aphasia?
Caramazza & Zurif 1976
Broca’s patients showed selective deficits in understanding sentences which needed correct decoding of syntactic relationships for correct understanding
pateints were tasked with choosing the picture within a pair that represented the cognitive content of a spoken sentence
most could be deduced from semantic information alone but improbable centre-embedded sentences were introduced where the implied syntactic relationships seemed semantically contradictory
e.g ‘the horse that the girl is kicking is brown’
errors were made such that patients would select the image consistent with semantic knowledge of horses kicking rather than the syntactic roles
suggests deficit in representations of syntactic information
caplan et al., 1985
the same deficit is seen if patients are given models to depict the scene in the sentence
so not due to demands/biasses introduced by use of picture matching stimuli
what does the neuroimaging literature say
Vingneau 2006
conducted a meta-analysis of functional neuroimaging studies investigating phonolgical, semantic and sentence processing in left hemisphere language areas (frontal, temporal, parietal)
used spatial clustering technique to process the 730 activation peaks - producing 30 activation clusters
broadly inferior frontal gyrus: phonological (dorsal), semantic (ventral) with the pars opercularis syntactic
A1 and motor mouth area: audio-motor loop for comprehension and production of syllables
posterior superior temporal gyrus: sentence and text processing
different WM perception-action loops identifiable for different language components (phonological loop medial frontal to posterior temporal)
authors argue this is evidence for a large-scale language network rather than modular organisation of language function
but activity during a language task is not the same as being necessary for this function as neuroimaging data is correlational
subsequently led to the development of dual-route theories and supports link between perception and action
how do theories of active perception link to language?
Pulvermuller & Fadiga 2010
Auditory input is necessary in informing the motor output of speech but the reverse relationship is less obvious
self-produced speech sounds stimulate the auditory system in the superior temporal cortex even when these are whispered and masked by noise
this activation increases with speech rate
suggestive of motor to auditory activation flow in the cortex during speech production
listening to speech sounds that require strong articulatory activity such as rolling r activates the motor system
hypothesised to constitute action-perception circuits where motor areas send back facilitatory excitatory projections to auditory perception areas
inferior frontal lesions can be understood in terms of degraded feedback activation
explains why right hemisphere lesions can result in Wernicke’s aphasia
TMS of lip and tongue in precentral cortex impairs phoneme identification in people listening to consonant-vowel syllables
stimulation of the lip resulted in d and t sounds (tongue related) as b and p (lip required in their production)
greater processing speed and accuracy for lip related sounds
reverse pattern seen with stimulation of the tongue
semantics - actions preferrentially performed with a particular body part activate motor and premotor areas in a somatotopic manner
theorised to extend to syntax as well but less strong - argued that circuits evolved to support sequential action can also support grammar as neurocomputational data indicated that word sequence processors are joined together to form circuits that provide a basis for higher-level syntactic structures leading to hierarchically nested sequences
what is the contribution of primary progressive aphasia to understanding of language and disorders
focal neurodegeneration/ atrophy of the brain in regions not typically damaged by stroke
e.g left inferior temporal cortex associated with progressive dissolution of modality-independent semantics
what evidence is there for deficits in both perceptual and semantic processing in WA?
word comprehension requires both phonemic processing and assignment of word meaning
McCarthy & Warrington
Robson et al., 2012
compared patients with WA, SD and semantic aphasia
patients impaired on nonverbal and verbal comprehension assessments
modality-input effects such as acoustic-phonological requirements increased, performance worsened
dual-deficits had separate neural correlates
acoustic-phonological analysis associated with posterior superior temporal gyrus
semantic cognition associated with posterior middle temporal gyrus
two deficits underlying WA rather than single impairment account
highlights the importance of understanding levels of processing and the limitations of studying large vascular lesions which do not respect functional boundaries
highlights steps in processing for accurate language comprehension
what is the wernicke-lichtheim model 1885
first modern model of brain function
interconnected functionally specialised regions account for the different patterns of deficits seen with different lesion sites
predicts
transcortical motor aphasia - poor spontaneous speech with good repetition and comprehension associated with damage to the SMA
transcortical sensory aphasia - fluent circumlocutory speech with semantic jargon and poor comprehension following posterior anterolateral thalamic and temporoparietal occipital junction lesions
but the modular nature of the theory necessarily limits the phenotypes it can account for
not always the case that lesions to these sites produce aphasia
- small lesions to BA produce temporary mutism but no significant disturbance of language function persists
- infarctions to operculum, capsulostriatal and periventricular areas result in BA
dronkers et al., 2000
isolated damage to superior temporal gyrus does not necessarily impede comprehension or reception
importance of connections - distributed language circuit and parallel processing streams
