Presentation on theme: "Neurological Basis for Speech and Language Helen Wills Neuroscience Institute University of."— Presentation transcript:
Neurological Basis for Speech and Language Helen Wills Neuroscience Institute University of California – Berkeley Bradley Voytek MCB 163: Mammalian Neuroanatomy 01 December, 2005
Speech vs. Language Speech The mechanical process of language such as articulation and phonation. Language The set of symbols we use for communication.
Elements of Speech & Language Phoneme Speech sounds /p/ or /b/ vs. ‘c’ in ace/cat /r/ and /l/ allophones in Japanese /p h / aspirated in Chinese vs. spin/pin allophone in English Morpheme Smallest language unit that carries meaning e.g., ‘dys-’ in dysfunction
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 ]
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…
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.
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.
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
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”
Language Studies No animal models are possible. If only humans have language, how do we study it? Dysfunction!
Language & Speech Disorders Jean-Paul Grandjean de Fouchy “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)
Aphasia Pierre Paul Broca 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)
Aphasia Carl Wernicke 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)
Speech & Language Regions
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
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.
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
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
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
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
MRI Video Patient Video Did you notice his right arm and hand?
Broca’s Aphasia Anterior insula
Broca’s Aphasia (2005) Anterior insula & arcuate fasciculus
Patient “Tan” Anterior insula & arcuate fasciculus
Paraphasia Neologistic Invention of new words: ‘glipt’ or ‘crint’ Semantic Word substitution, similar meaning: ‘knife’ for ‘spoon’ Phonemic Sound substitution: ‘scoon’ for ‘spoon’ Often a feature of other aphasias
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
Wernkicke’s Aphasia MRI Video Patient Video 1 Patient Video 2
Wernkicke’s Aphasia – Sign Language
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
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
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
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
Global Aphasia Damage so widespread is usually caused by MCA infarct
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
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
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
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”
Induced Aphasias Wilder Penfield (1952) Intraoperative mapping of “elegant cortex” before surgery Cortical stimulation caused speech arrest
Induced Aphasias Berger (2005) Penfield’s techniques are still being used today Mouth Motor
Induced Aphasias Speech Arrest
Induced Aphasias Anomia
Transcranial Magnetic Stimulation (TMS) APs propagate Creates charge difference along axon Summed across millions of neurons Stimulation can induce transient aphasias
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.
Electroencephalography (EEG) Signal sources are: APs propagate Creates charge difference along axon Summed across millions of neurons
Event-related Potentials Averaged, stimulus-locked EEG signal Many different forms depending on stimulus Most well-studies is the P300 Most well-studied in language is the N400
Functional Magnetic Resonance Imaging (fMRI) Responses to words Some fMRI studies of bilingual subjects indicate that different languages share neural components, but have some differences
Conclusions Language appears to be an innate feature of humans. This innateness appears to have neurological origins. As a human-specific trait, language is difficult to study. Clinical observation of aphasias—combined with neuroimaging—offers insights into neurolinguistics. However, knowing which region is important offers little information as to how these regions play their roles.
Cheers: Dr. Jeff Winer and John Schlerf Dr. Bob Knight All of Fall ’05 MCB 163