Neurological Basis for Speech and Language [email protected] Helen Wills Neuroscience Institute University of.

Neurological Basis Neurological Basis for Speech and for Speech and

LanguageLanguage

[email protected]@berkeley.edu

http://socrates.berkeley.edu/~btvoytekhttp://socrates.berkeley.edu/~btvoytek

Helen Wills Neuroscience InstituteHelen Wills Neuroscience InstituteUniversity of California – BerkeleyUniversity of California – Berkeley

Bradley VoytekBradley Voytek

MCB 163: Mammalian NeuroanatomyMCB 163: Mammalian Neuroanatomy01 December, 200501 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

• /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

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

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

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

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