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1 Language Chris Rorden Aphasia: Broca’s, Wernicke’s, etc. Alexia Anomia Dyslexia Agraphia Split brain patients Disconnection syndromes

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Presentation on theme: "1 Language Chris Rorden Aphasia: Broca’s, Wernicke’s, etc. Alexia Anomia Dyslexia Agraphia Split brain patients Disconnection syndromes"— Presentation transcript:

1 1 Language Chris Rorden Aphasia: Broca’s, Wernicke’s, etc. Alexia Anomia Dyslexia Agraphia Split brain patients Disconnection syndromes

2 2 Background (from c82bio) Localization –Certain regions devoted to specific tasks. –Broca, Gall –Based on (almost) no evidence Equipotentiality –Whole brain involved with tasks –Flourens (1840s), Head, Lashley Both correct/wrong.

3 3 Language Distinctly human? Superior to other animals Is there a single anatomical basis?

4 4 Language Production Broca’s Area (1861) Difficulty in speech production Loss of ability to repeat speech Comprehension intact Foot of 3 rd frontal convolution (BA 44) Left hemisphere (1865) –Except left handers

5 5 Language Comprehension Wernicke’s Area (1874) Normal production (speech sounds and fluent nonsense) Sounds okay if you do not know the patient’s language (e.g. Chinese Wernicke’s aphasic would sound fine to me) Unaware of deficit Impaired comprehension Left hemisphere Superior temporal gyrus (BA 42, 22)

6 6 Wernicke’s prediction Predicted two language centers: –Broca’s Area: speech articulation. –Wernicke’s Area: language comprehension. Predicted 3 rd Syndrome: –Disconnection syndrome –‘Conduction aphasia’ –Damage to arcuate fasciculus

7 7 Conduction aphasia Can comprehend speech Articulation is intact Difficulty in repeating speech Lesions in Temporal Parietal Junction that knock out underlying white matter Patients with damage ONLY to the arcuate fasciculus can still generate speech. –Why? Other pathways

8 8 Wernicke-Lichtheim (1885) Schema From auditory input (a) to motoric articulation of speech (m) Broca’s Aphasia Wernicke’s Aphasia Concepts (Distributed) Conduction aphasia

9 9 4: Transcortical Motor Aphasia Disconnection of Broca’s from concepts Speech is slow, terse Can comprehend speech Found after damage to the frontal lobes Unlike Broca’s Aphasics, can repeat phrases when spoken to –direct Wernicke’s to Broca’s pathway intact

10 10 6: Transcortical Sensory Aphasia Disconnection of Wernicke’s from concepts Can repeat words Speech is articulate nonsense Unable to comprehend speech Found after damage to the posterior language area

11 11 7 Pure Word Deafness Loss of ability to understand spoken speech. Normal speech, reading, writing Behaviour and anatomy dissociate from Wernicke’s aphasia Written comprehension intact, intact written/verbal production.

12 12 Specifically language Aphasics unable to use speech to convey information. However, aphasics can often cite memorized texts –Songs –Prayers, verses –Cliché

13 13 Exceptions to the rule Dronkers et al [2000] note exceptions to anatomy Traditional Theory: –JC will have Broca’s and MC will have Wernicke’s Aphasia –JH and OB will not have aphasia Reality: –Neither JC or MC has Aphasia –JH has Broca’s and OB has Wernicke’s Aphasia. Broca’sWernicke’s

14 14 Exceptions to the rule Patients with similar lesions can show very different behaviour. What are the implications? Are these exceptions to rule worth worrying about? –Perhaps we can not see functional extent of OB/JHs lesion But JC/MC clearly have damage in areas associated with language deficits. –Different brains develop differently –Group studies required

15 15 Brain areas vary between people Broca’s Area = Brodmann’s 44/45 BA44/45 vary between people Perhaps Broca was right, but JC and JH have slightly unusual locations for these regions. Group studies required to resolve this question. Textbook Location of Broca’s Area Actual location of BA44/45 based on histology for two people. Very different size/location (Amunts et al., 2004 NeuroImage 22, 42-).

16 16 Broca’s Aphasia Broca’s Aphasia is a syndrome: association of deficits. –‘Telegraphic’ speech: Produce content words with few grammatical markers, pauses between words –Apraxia of Speech: distortion of speech sounds (‘yawyer’ instead of lawyer), poor prosody, stress on wrong syllable without motor problems for non- speech movements. –Dysarthria: poor control of muscles used in articulation –Word finding –Repetition –Comprehension: problems with complex grammar.

17 17 Problems with traditional model Does this cluster of symptoms reflect one functional module, or separate anatomical neighbours? Comprehension: Broca’s not simply problem in speech production –Intact: ‘the boy kissed the girl’ –Problems: ‘the girl was kissed by the boy’ Is comprehension specific to speech, or due to attentional/working memory problems?

18 18 Fractionation of Broca’s Aphasia Dronkers et al (1994) examined > 100 aphasics Comprehension deficits associated with Broca’s Aphasia appear to correlate with Temporal Lobe damage. Suggests association due to neighbouring centers, not shared function. Finding confirmed in neuroimaging studies (Bavelier et al. 1997). Broca’s Area (BA44/45) Region identified by Dronkers

19 19 Reflections Dronkers suggests grammatical problems not due to Broca’s Area Used low quality structural scans –See Hillis et al. for critique. Brain (2004), 127,

20 20 Apraxia of Speech Dronker’s [1996, Nature, 384, ] AoS: disorder of shaping the vocal tract for a particular speech sound. Studied 25 apraxic and 19 control patients. –Tested 1 year after lesion: deficits are stable. –All AoS had damage to portion of insula. –This region was spared in all controls. –Region near motor strip [M1] for mouth. ApraxicsControls

21 21 Apraxia of Speech Dronkers (1996) suggest that insular damage causes AoS. –Supported by Shuren,, 1993; Donnan et al., 1997; Bates et al., 2003). Hillis et al. (2004; Brain ) disagree: argue Broca’s Area critical for AoS. –Dronker’s examined chronic patients with structural scans. –Hillis examined acute patients and found that patients with AoS had perfusion deficits in Broca’s Area, even if these were not seen in structural scans.

22 22 Wernicke-Lichtheim (1885) Schema From auditory input (a) to motoric articulation of speech (m) Broca’s Aphasia Wernicke’s Aphasia Concepts (Distributed) Conduction aphasia

23 23 Aphasia Notes [ ]

24 24 Aphasia notes Anomic: problem naming objects Paraphasia: use of related but inappropriate words –Semantic: ‘fork’ when ‘knife’ is meant –Phonemic: ‘fork’ when ‘stork’ is meant Neologism: literally “new word,” using word that bears no obvious relation to a recognizable word. e.g., “glester” Paragrammatic: incorrect use of grammatical function words. e.g., “he is always brillianting”

25 25 Recovery from aphasia Many aphasics get better –Is this due to intact tissue on damaged left? –Or does right hemisphere take over? Warburton et al. (1999) examined recovered aphasics. –Many controls show left-only activity [far left] –Others show bilateral activity, but predominantly left [2 nd from left] –Patients show different patterns of activity: for some, intact regions on damaged side have become active.

26 26 Musical Syntax Musical syntax is processed in Broca's area. Non-musicians listen to 5 chords harmonically inappropriate chords generate early right-anterior negativity (ERAN), measured with MEG. Inferior BA44 source of ERAN (Broca’s source and right homologue). Maess et al. (2001) Nature Neuroscience 4, 540 – 545.

27 27 Reading and writing Wernicke’s aphasics: language comprehension –Regardless whether spoken or written Broca’s aphasics: speech production –Primarily spoken (except grammar) Are there specific reading centres?

28 28 Alexia with agraphia Déjerine, 1891: Damage to the angular gyrus (BA 39) leads to –‘Alexia with agraphia’ reading & writing deficits –Intact speech comprehension

29 29 Alexia without agraphia Disconnection of angular gyrus from visual inputs –Language outputs intact –Patients cannot read –Writing preserved Rare: left and right pathways to angular gyrus Requires damage to 1. posterior callosum 2. left occipital lobe Without damage to left angular gyrus

30 30 Reading Vision vs Braille Fusiform gyrus also involved with reading Büchel et al. (1998) Nature, 394, –3 Groups: Sighted Early Blind Congenitally Blind –Reading activates fusiform gyrus (relative to speech). –Fusiform not simply visual area.

31 31 Language and laterality Language mainly LEFT hemisphere task –Broca’s/Wernicke’s patients left hemisphere –Wada Test [Intracarotid amobarbital procedure] temporarily disables one hemisphere Virtually all right handers have language in left Left Handers: –70% like right handers –15% language on right (reversed) –15% distributed language (bilateral)

32 32 Brain asymmetries (Toga & Thompson, 2003) Right frontal and left occipital protrude relative to counterpart Skull imprints called ‘petalia’ Cortical structures (sulci) shifted as well (‘Yakovlevian torque’) Cortical Assymetries Left occipital: wider, protrudes posteriorly Right frontal: wider, protrudes anteriorly

33 33 Brain asymmetries Sylvian fissure (SF) and superior temporal sulcus (STS) also differ between left and right. Left SF/STS more posterior Planum temporale (posterior-ventral face of STS) larger on left. See Martin’s Human Neuropsychology for more asymmetries.

34 34 Corpus callosum Fiber tract between left and right side of the brain. –200 million axons –Primarily homotopic: connects corresponding region (Lparietal- Rparietal, Lfrontal-Rfrontal) –Also Heterotopic: connecting different regions (Lfrontal- Rparietal).

35 35 Split brain patients Complete or partial commissurotomy –1950s operation for intractable epileptics –Unseen objects Identified when presented to right hand Verbally unidentified when presented to left hand, though hand can select matching object –Visual stimuli (briefly flashed) Verbally describe items presented to right field Unable to name items in left field, though can choose correct item with left hand –Spatial tasks: suggest right hemisphere better (Nebes, 1978).

36 36

37 37 Alien Hand Syndrome Alien hand syndrome [Brion and Jedynak; 1972] –Split brain patients do not recognize their unseen left hand when touched by right hand. –‘intramanual conflict’: e.g. one hand buttons up shirt, other unbuttons. –Left hand spontaneously engages in actions that the patient says they are not intending: acts foreign, alien or uncooperative. –Seen in other patients: Goldberg et al (1981) report similar effects in patients with mesial-frontal/callosal lesions –AKA ‘wayward hand’, ‘anarchic hand’

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