Transcript Document

Language Has Both Learned and Innate Components
Humans have highly specialized language in which arbitrary
symbols or behaviors are assembled and reassembled in almost
infinite.
All languages have similar basic elements:
• Phonemes—basic speech sounds
• Morphemes—simple units of meaning
• Semantics—meanings of words or sentences
• Syntax—grammatical rules for constructing phrases and
sentences
From birth, babies can distinguish phonemes from any language.
Language development depends on experience during a sensitive
period, a time when an organism can be permanently altered by
a particular experience or treatment.
Effects of Isolation on Birdsong Development
Song Control Nuclei of the Songbird Brain
Elicitation of Vocalizations by Electrical Stimulation of the
Monkey Brain
Language Has Both Learned and Innate Components
Chimpanzees and gorillas can learn other systems of
communication:
• American Sign Language (ASL)
• Use arbitrary colored tokens or computerized symbols in
ways that seem to reflect an acquired ability to form short
“sentences”—novel, meaningful chains made up of basic
units of meaning.
• Kanzi (a bonobo) learned to use symbols in novel ways
through observational learning rather than through intense
training.
Chimpanzee Using Symbols
American Sign Language
A Heritable Language Disorder
Language Disorders Result from Region-Specific
Brain Disorders
M. Leborgne could only utter the syllable “tan” after a brain
injury.
Study of this brain and similar cases led Paul Broca to identify
a region in the anterior left hemisphere that is specialized
for speech.
Broca’s area—region of the inferior frontal lobe that is
involved in speech production
Aphasia—an impairment in language ability caused by brain
injury, usually to the left hemisphere
The Wada test determines involvement of hemispheres in
language by anesthetizing each hemisphere separately using
sodium amytal.
The Brain of “Tan”
The Wada Test
Language Disorders Result from Region-Specific
Brain Disorders
Prominent signs of aphasia:
Paraphasia—substitution for a word by a sound, incorrect word, or
unintended word
Neologism—an entirely novel nonsense word
Nonfluent speech—talking with considerable effort, in short
sentences, and without the usual melodic character of
conversational speech
Many patients with aphasia may also show other impairments:
• Agraphia—inability to write
• Alexia—inability to read
• Apraxia—a motor impairment in the ability to begin and execute
skilled voluntary movements, even though there is no muscle
paralysis.
Brain Lesions That Produce Aphasia
Language Symptomatology in Aphasia
Cortical Speech and Language Areas in Humans
PET Scans of Brain Activation in Progressively
More-Complex Language Tasks
Functional Neuroimaging Tracks Activity in the
Brain’s Language Zones
Word processing has different levels:
1. Passive exposure to seen words (posterior area of
left hemisphere)
2. Passive exposure to spoken words (temporal lobes)
3. Oral repetition (motor cortex of both sides, the
supplementary motor cortex, and a portion of the
cerebellum and insular cortex)
4. Generation of a semantic association to a word
(language-related regions in the left hemisphere,
including Broca’s area)
Electrical Stimulation of Some Brain Sites Can Interfere with Language
Mapping Language Areas
“invasive pre-surgery mapping techniques, such as electrocortical stimulation
(bottom), which requires a patient to be awake and conversant while surgeons
probe exposed brain areas in an effort to locate and map language-related
functions.” Better brain imaging helps surgeons avoid damage to language functions November 4, 2003 By Gerry
Everding http://news.wustl.edu/news/Pages/494.aspx
The Traditional Connectionist Model of Aphasia
Towards a New Neurobiology of Language
• Neurobiological measures to study language
• deficit-lesion correlations in stroke patients
• electrophysiological data from electroencephalographic
• intracranial recordings associated with surgical interventions
• Wada test for language lateralization
• The “classical model” of language
• Based on Broca, Wernicke and Lichtheim
• Contemporary model from Geschwind
• New Neurobiology
• Much better brain scan resolution
• Integrated with cognitive psychology and linguistics
Reading Skills Are Difficult to Acquire and
Frequently Impaired
Dyslexia—a reading disorder attributed to brain impairment
Acquired dyslexia (alexia) can occur in adults after injury to the
left hemisphere.
Deep dyslexia is an acquired dylexia where patients read a word
as another with a related meaning.
In surface dyslexia, another acquired dylexia, the patient is
restricted to the details and sounds of letters.
Surface dyslexics find it difficult to recognize words in which
the letter-to-sound rules are irregular.
Surface dyslexia doesn’t occur in native speakers of languages
that are perfectly phonetic (such as Italian).
Types of Dyslexia
• Developmental
– Primary if from genetic abnormalities
• Some genes related to brain development
– Secondary if from abnormal prenatal through
childhood development, including neglect.
• Acquired (alexia) if caused by brain trauma
– Deep problems with whole word recognition related
in meaning, cow for horse
– Surface difficulty with words that have irregular
letter-to-sound rules
Developmental Dyslexia
• Not from low intelligence
• Not a visual problem such as letter reversal
• “an unexpected difficulty learning to read despite
intelligence, motivation and education.”
– Dyslexic children takes longer to learn how to talk.
– While the language area of the brain is slower to develop,
motor control skills come easier.
– Dyslexics tend to learn how to walk earlier than other
children.
– Dyslexics have the higher rate of depression and suicide
– Are less likely to finish high school or college.
Developmental Dyslexia
• Disorganized circuits
– Mostly in the temporal lobes
– Some amount in frontal cortex
• Genetic predisposition related to neuronal migration
early in development which produces
– micropolygyria
– ectopias
– dysplasias
• Processing deficits appear as early as 6 months
• Difficulties processing consonant duration
• Disorganized cortical connections
– Disrupts flow of information to the inferior temporal region
Reading Skills Are Difficult to Acquire and
Frequently Impaired
Developmental dyslexia occurs in 5% of children who have
trouble learning to read.
Brains of dyslexics show unusual arrangements of cortical cells.
Micropolygyria—small regions of excessive number of gyri or
cortical foldings
Ectopias—clusters of extra cells
Neural Disorganization in Dyslexia
Developmental Dyslexia Treatment
• Treated through education, and the sooner intervention begins, the
better.
– Learn to recognize the smallest sounds that make up words (phonemes)
– Understand that letters and strings of letters represent these sounds
• An increase in left-temporo-parietal and left inferior frontal
activity after training
• Also increased activity in right side frontal, temporal and anterior
cingulate gyrus
• Magnitude of increased activation in left temporo-parietal cortex
correlated to improvement in oral language and improved reading