LECTURE 17 – BIOLOGY OF LANGUAGE
LATERALIZATION
Lateralization = specialization of a function in one hemisphere of the brain or the other.
The human brain is divided into 2 hemispheres: the left hemisphere & the right
hemisphere.
Lateralization suggests that certain cognitive fcts & processes are more dominant in one
hemisphere than the other.
Language is largely a lateralized fct.
In most people (90% of total pop), the left hemisphere is dominant for speech &
language fcts.
Knecht & colleagues (2000) assessed the
relationship between handedness & lateralization
of speech mechanisms in people without any
known brain damage.
They used an imaging procedure to measure
changes in cerebral blood flow while people
performed a verbal task.
The WADA test (named after Dr. WADA) = medical procedure used to assess hemispheric
(left or right) dominance for language & memory fct in the brain.
Selectively anesthetize one hemisphere with Sodium Amytal.
Anesthetize the left hemisphere & see if language is impaired.
Anesthetize the right hemisphere & see if language still works.
Highly invasive
Less invasive methods:
- Transcranial Magnetic Stimulation (TMS)
Disrupting the fcts of one of the hemispheres with TMS & see if language is
impaired.
- Neuroimaging
On the other hand, the right hemisphere is dominant for prosody, as well as expressing &
recognizing emotions in the tone of voice.
Prosody = rhythmic, empathic, & melodic aspects of speech.
In a functional-imaging study by Meyer & colleagues (2002), participants heard normal
sentences or sentences that contained only the prosodic elements of speech with the
meaningful sounds filtered out.
, Results showed:
- The meaningful components of speech
primarily activated the left hemisphere (blue &
green regions).
- The prosodic components primarily activated
the right hemisphere (orange & yellow
regions).
Both hemispheres of the brain contribute to our language abilities in diff ways.
The importance of lateralization is also revealed through studies of patients who have
undergone split-brain operation (= involves surgically severing the corpus callosum to isolate
each cerebral hemispheres).
Sometimes used to treat very severe seizure disorders, when neurons in one side of the
brain becomes uncontrollably overactive, & the overact is transmitted to the other side of
the brain by the corpus callosum.
ORGANISATION IN LANGUAGE PROCESSING: WERNICKE-GESCHWIND MODEL
Wernicke-Geschwind model = classical neurological model explaining the neural
organization of language.
It outlines a series of connections between diff brain regions to explain language fcts,
particularly those related to language comprehension & prod.
Speech
In the context of this model, speech is understood as a complex process involving several
interconnected brain regions:
1. Auditory processing: speech process begins in the primary auditory cortex, where
auditory info is received & initially processed.
This includes the perception of spoken language.
2. Wernicke’s area (language comprehension): the processed auditory info is then sent
to Wernicke’s area.
This area is primarily associated with language comprehension.
3. Arcuate fasciculus (connection between Wernicke’s & Broca’s areas): it serves as
the neural pathway connecting these 2 areas.
It allows for the transfer of info between the regions responsible for language
comprehension & language prod.
4. Broca’s area (language prod): plays a crucial role in the planning & execution of the
motor mov required for speech.
5. Motor cortex & primary motor cortex
Signals from Broca’s area are then sent to the motor cortex, which is involved in
coordinating the mov of the muscles required for speech prod.
The primary motor cortex is responsible specifically for executing these mov.
, The angular gyryus is not explicitly
included in the Wernicke-Geschwind
model.
But it’s an important region associated
with language.
Semantic processing
Reading & word retrieval
Reading
The process goes as follows:
1. Primary visual cortex (visual processing): process begins with the visual perception
of written symbols, such as letters & words.
The primary visual cortex is responsible for processing the basic features of these
symbols, including their shapes, sizes, & orientations.
2. Angular gyrus: region in the parietal lobe.
It contributes to semantic processing, & aids in the comprehension of written
language processed by the primary visual cortex.
3. Wernicke’s area: plays a role in understanding the meaning of written words.
Also helps with processing syntactic & semantic aspects of written language.
4. Arcuate fasciculus: transfers info from Wernicke’s area to Broca’s area.
5. Broca’s area & motor cortex: in reading aloud or silently, these 2 regions are involved
in the planning & execution of the motor mov required for speech or inner speech
during reading.
Language is unique to humans
LATERALIZATION
Lateralization = specialization of a function in one hemisphere of the brain or the other.
The human brain is divided into 2 hemispheres: the left hemisphere & the right
hemisphere.
Lateralization suggests that certain cognitive fcts & processes are more dominant in one
hemisphere than the other.
Language is largely a lateralized fct.
In most people (90% of total pop), the left hemisphere is dominant for speech &
language fcts.
Knecht & colleagues (2000) assessed the
relationship between handedness & lateralization
of speech mechanisms in people without any
known brain damage.
They used an imaging procedure to measure
changes in cerebral blood flow while people
performed a verbal task.
The WADA test (named after Dr. WADA) = medical procedure used to assess hemispheric
(left or right) dominance for language & memory fct in the brain.
Selectively anesthetize one hemisphere with Sodium Amytal.
Anesthetize the left hemisphere & see if language is impaired.
Anesthetize the right hemisphere & see if language still works.
Highly invasive
Less invasive methods:
- Transcranial Magnetic Stimulation (TMS)
Disrupting the fcts of one of the hemispheres with TMS & see if language is
impaired.
- Neuroimaging
On the other hand, the right hemisphere is dominant for prosody, as well as expressing &
recognizing emotions in the tone of voice.
Prosody = rhythmic, empathic, & melodic aspects of speech.
In a functional-imaging study by Meyer & colleagues (2002), participants heard normal
sentences or sentences that contained only the prosodic elements of speech with the
meaningful sounds filtered out.
, Results showed:
- The meaningful components of speech
primarily activated the left hemisphere (blue &
green regions).
- The prosodic components primarily activated
the right hemisphere (orange & yellow
regions).
Both hemispheres of the brain contribute to our language abilities in diff ways.
The importance of lateralization is also revealed through studies of patients who have
undergone split-brain operation (= involves surgically severing the corpus callosum to isolate
each cerebral hemispheres).
Sometimes used to treat very severe seizure disorders, when neurons in one side of the
brain becomes uncontrollably overactive, & the overact is transmitted to the other side of
the brain by the corpus callosum.
ORGANISATION IN LANGUAGE PROCESSING: WERNICKE-GESCHWIND MODEL
Wernicke-Geschwind model = classical neurological model explaining the neural
organization of language.
It outlines a series of connections between diff brain regions to explain language fcts,
particularly those related to language comprehension & prod.
Speech
In the context of this model, speech is understood as a complex process involving several
interconnected brain regions:
1. Auditory processing: speech process begins in the primary auditory cortex, where
auditory info is received & initially processed.
This includes the perception of spoken language.
2. Wernicke’s area (language comprehension): the processed auditory info is then sent
to Wernicke’s area.
This area is primarily associated with language comprehension.
3. Arcuate fasciculus (connection between Wernicke’s & Broca’s areas): it serves as
the neural pathway connecting these 2 areas.
It allows for the transfer of info between the regions responsible for language
comprehension & language prod.
4. Broca’s area (language prod): plays a crucial role in the planning & execution of the
motor mov required for speech.
5. Motor cortex & primary motor cortex
Signals from Broca’s area are then sent to the motor cortex, which is involved in
coordinating the mov of the muscles required for speech prod.
The primary motor cortex is responsible specifically for executing these mov.
, The angular gyryus is not explicitly
included in the Wernicke-Geschwind
model.
But it’s an important region associated
with language.
Semantic processing
Reading & word retrieval
Reading
The process goes as follows:
1. Primary visual cortex (visual processing): process begins with the visual perception
of written symbols, such as letters & words.
The primary visual cortex is responsible for processing the basic features of these
symbols, including their shapes, sizes, & orientations.
2. Angular gyrus: region in the parietal lobe.
It contributes to semantic processing, & aids in the comprehension of written
language processed by the primary visual cortex.
3. Wernicke’s area: plays a role in understanding the meaning of written words.
Also helps with processing syntactic & semantic aspects of written language.
4. Arcuate fasciculus: transfers info from Wernicke’s area to Broca’s area.
5. Broca’s area & motor cortex: in reading aloud or silently, these 2 regions are involved
in the planning & execution of the motor mov required for speech or inner speech
during reading.
Language is unique to humans
