Document

MCB 163: Mammalian Neuroanatomy
01 December, 2005
Neurological Basis for
Speech and Language
Bradley Voytek
Helen Wills Neuroscience Institute
University of California – Berkeley
[email protected]
http://socrates.berkeley.edu/~btvoytek
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
• /ph/ 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 - 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)
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
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
Speech & Language Regions
Broca’s Area
Wernicke’s Area
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
Brodmann’s Areas
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
Broca’s Aphasia
Broca’s Aphasia
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
Nina Dronkers
Patient “Tan”
Anterior insula & arcuate fasciculus
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’
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
Global Aphasia
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

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