Neurological Basis for Speech and Language

1. Neurological Basis for Speech and Language MCB 163: Mammalian Neuroanatomy 01 December, 2005 Bradley Voytek Helen Wills Neuroscience Institute University of California – Berkeley btvoytek@berkeley.edu http://socrates.berkeley.edu/~btvoytek

2. Speech vs. Language • Speech • The mechanical process of language such as articulation and phonation. • Language • The set of symbols we use for communication.

3. Elements of Speech & Language • Phoneme • Speech sounds • /p/ or /b/ vs. ‘c’ in ace/cat • /r/ and /l/ allophones in Japanese • /ph/ aspirated in Chinese vs. spin/pin allophone in English • Morpheme • Smallest language unit that carries meaning • e.g., ‘dys-’ in dysfunction

4. Elements of Speech & Language • Syntax • “Colorless green ideas sleep furiously” vs. • “Sleep colorless furiously ideas green” • “I shot an elephant in my pajamas” – Groucho Marx [ I shot ] [ an elephant ] [ in my pajamas ] or [ I shot ] [an elephant in my pajamas ]

5. Elements of Speech & Language • Semantics & Pragmatics • “The quarterback threw the ball.” • “The princess went to the ball.” • “The dancer pivoted on the ball of her foot.” • Intonation, Prosody, etc. • Hey. • Hey! • Hey…

6. Human Language • Every human culture has a language • Language Acquisition • Children understand ~13,000 words by age 6 • They understand ~60,000 by 18 • Babies discriminate sounds their parents cannot (e.g., /r/ and /l/ in Japanese) • This discriminability begins to disappear at 10 mos.

7. Human Language • Innateness • In 1959, Noam Chomsky postulated an innate neural circuitry dedicated to language. • Stages of acquisition are relatively invariant across cultures. • Is innateness for patterns in general, or language specifically? • Deprived of social environment, children will create languages.

8. Importance of Language • Sapir-Whorf Hypothesis • Language affects thought. • Effects go beyond intrapersonal communication. • “Snow” (Eskimo myth and skiing) vs. “building”. • Hopi had one word for all things not a bird that fly. • Color studies (Classic Greek blue/black) • Number studies (1, 2, >2) • Neurolinguistic Programming (NLP) • A proposed idea that through language you can affect another’s perception and cognition

9. Language Evolution • Bees dance in stereotyped ways • Other animals mimic human speech • Simians might learn gesture/object associations • Only humans spontaneously learn and create languages • Wednesday Headline: “Monkeys have accents too, experts say”

10. Language Studies • No animal models are possible. • If only humans have language, how do we study it? Dysfunction!

11. Language & Speech Disorders Jean-Paul Grandjean de Fouchy - 1784 “Toward the end of dinner, I felt a little increase in pain above the left eye, and in that very instant I became unable to pronounce the words I wanted. I heard what was said, and I thought of what I ought to reply, but I spoke words other than those which would express my thoughts… This sort of paroxysm lasted about a minute, and during its course my mind was clear enough to notice this singular distinction in the sensorium, which had only one of its parts affected, without any of the others experiencing the least derangement.” (Hoff, Guillemin & Geddes, 1958, p. 447)

12. Aphasia • Patient “Tan” (Leborgne) • Could answer questions with gestures • Could say a few curse words, “tan” • Broca hoped to disprove cortical specialty • In autopsy, found an abscess in Tan’s brain • 1865 paper showed localization to left frontal lobe (Broca’s area) Pierre Paul Broca

13. Aphasia • Another region? • Not all language disturbances were speech • Not all disturbances involved Broca’s area • Loss of words comprehension • 1874 paper showed localization to left temporal lobe (Wernicke’s area) Carl Wernicke

14. Speech & Language Regions

15. Broca’s Area

16. Wernicke’s Area

17. Speech & Language Regions • Broca’s (BA 44, 45): Inf prefrontal gyrus • Wernicke’s (BA 22): Post sup temporal gyrus at the T-P junction • Arcuate fasciculus: Axon tract connecting Broca’s with Wernicke’s

18. Brodmann’s Areas

19. Language Laterality • Speech is supported by entire motor system. • Language is subserved by the left hemisphere in: • 98% in right-handed males; • 90-95% in right-handed females. • Language is subserved equally by the left, right, or both hemispheres among left-handers.

20. Clinical Observation • There are many subtle differences to each aphasic case. • These subtle differences, combined with neuroimaging and anatomical localization, can lead to building a neurological model for language

21. Speech & Language Disorders • Aphasia • A disturbance of language with a breakdown in grammar and syntax often associated with anomia or paraphasias. • Auditory: speaking, comprehension • Visual: reading, sign language • Tactile: Braille

22. Types of Disorders • Broca’s & expressive aphasias • Wernicke’s & receptive aphasias • Transcortical motor aphasia • Transcortical sensory aphasia • Conduction aphasia • Global aphasia • Subcortical aphasia • Anomia • Alexia • Apraxia

23. Broca’s Aphasia • Nature • True Broca’s aphasia manifests with damage to several areas including: • Broca’s area • Left insula • Left arcuate fasciculus • Symptoms • Loss of fluency and articulation • Inability to repeat complex sentences • Impaired comprehension of complex sentences

24. Broca’s Aphasia

25. Broca’s Aphasia MRI Video Patient Video • Did you notice his right arm and hand?

26. Broca’s Aphasia Anterior insula

27. Broca’s Aphasia (2005) Anterior insula & arcuate fasciculus

28. Nina Dronkers

29. Patient “Tan” Anterior insula & arcuate fasciculus

30. Paraphasia Often a feature of other aphasias • Neologistic • Invention of new words: • ‘glipt’ or ‘crint’ • Semantic • Word substitution, similar meaning: • ‘knife’ for ‘spoon’ • Phonemic • Sound substitution: • ‘scoon’ for ‘spoon’

31. Wernicke’s Aphasia • Nature • Caused by damage to Wernicke’s area. • Symptoms • Effortless, melodic speech • Unintelligible content due to word and phoneme choice errors (phonemic paraphasias) • Loss of repetition

32. Wernkicke’s Aphasia MRI Video Patient Video 1 Patient Video 2

33. Wernkicke’s Aphasia – Sign Language

34. Transcortical Motor Aphasia • Nature • Similar to Broca’s aphasia: • Damage is in region anterior to Broca’s area • Symptoms • Again, similar to Broca’s aphasia: • Loss of fluency and articulation • Intact repetition

35. Transcortical Sensory Aphasia • Nature • Similar to Wernicke’s aphasia: • Damage is in region inferior to Wernicke’s area • Symptoms • Again, similar to Wernicke’s aphasia: • Effortless, melodic speech • Unintelligible content due to word and phoneme choice errors (phonemic paraphasias) • Intact repetition

36. Conduction Aphasia • Nature • Damage along the temporal-parietal junction: • Left superior temporal gyrus • Left inferior parietal lobe • Left arcuate fasciculus (maybe only damage required) • Symptoms • Relatively intact comprehension and speech production • Some phonemic paraphasic errors • Loss of repetition

37. Global Aphasia • Nature • Widespread damage including: • Basal ganglia • Insula • Broca’s area • Wernicke’s area • Superior temporal gyrus • Symptoms • Like Broca’s, Wernicke’s, and conduction aphasias together: • Loss of language comprehension • Loss of speech production • Loss of repetition

38. Global Aphasia • Damage so widespread is usually caused by MCA infarct

39. Global Aphasia

40. Subcortical Aphasia • Nature • Due to damage of subcortical structures: • Left thalamus, or • Left caudate • Symptoms • Impaired language production • Dysarthria: dysfunction of mouth and larynx muscle control

41. Anomia • Nature • Caused by lesion to left parietal, posterior to Wernicke’s • Symptoms • Highly specific deficit • Difficulty in remembering words • Perfectly normal speech and fluency otherwise

42. Alexia & Agraphia • Nature • Vision-dependent (also known as “word blindness”) • Disruption of transfer of vision to lateralized speech areas • Splenium allows transfer between visual hemispheres • Symptoms • Alexia: disruption of ability to read • Dyslexia: inability to understand more than a few lines of text • Agraphia: disruption of ability to write • Splenium damage disrupts reading in the left visual field

43. Apraxia • Nature • Seen in approximately 1/3 of all aphasics • Caused by lesion to precentral gyrus of the insula • Symptoms • Difficulty in mouth movement sequences: • “Open your mouth, stick out your tongue, pucker your lips”

44. Induced Aphasias • Wilder Penfield (1952) • Intraoperative mapping of “elegant cortex” before surgery • Cortical stimulation caused speech arrest

45. Induced Aphasias • Berger (2005) • Penfield’s techniques are still being used today Mouth Motor

46. Induced Aphasias Speech Arrest

47. Induced Aphasias Anomia

48. Transcranial Magnetic Stimulation (TMS) • APs propagate • Creates charge difference along axon • Summed across millions of neurons • Stimulation can induce transient aphasias

49. Transcranial Magnetic Stimulation (TMS) • Easiest to map cortical motor areas via EMG. • Perception of visual or auditory speech increase excitability of orofacial muscles. • Combined PET/TMS indicates that increased TMS excitability correlates to Broca’s area activity.

50. Electroencephalography (EEG) Signal sources are: • APs propagate • Creates charge difference along axon • Summed across millions of neurons