Download Fig. 14-2, p. 418

1 9 . Langua ge and Lat eralizat ion
Language
Evolut ion
Anato mical
Deve lopment al
Animal models
Neurology
Broca’s area
Wernicke’s area
Language a nd m emory
Lat eralizat ion
Anat om y
Funct ion
Evolution and Physiology of
Language
• Human language is a complex form of
communication.
• Compared to other species, human language
has high productivity.
– Productivity - the ability to produce new signals
to represent new ideas.
Stroop Effect 1: read the words
Stroop Effect 1: read the words
Stroop Effect 2: name the colors
Stroop Effect 2: name the colors
Stroop Effect 3: physiology
Although the functions of the anterior cingulate are very
complex, broadly speaking it acts as a conduit between
lower, somewhat more impulse-driven brain regions and
higher, somewhat more thought-driven behaviors. The
Stroop effect's sensitivity to changes in brain function may
be related to its association with the anterior cingulate.
1 9 . Langua ge and Lat eralizat ion
Language
Evolut ion
Anato mical
Deve lopment al
Animal models
Neurology
Broca’s area
Wernicke’s area
Language a nd m emory
Lat eralizat ion
Anat om y
Funct ion
Evolution and Physiology of
Language
• Two categories of theories attempt to
explain the human ability to learn language
more easily than other species.
1. “Language evolved as a by-product of overall
brain development.”
2. “Language evolved as an extra part of the
brain.”
Evolution and Physiology of
Language
• Problems associated with the “language as
a by-product of increased intelligence”
theory:
1. People with a full-size brain and normal
overall intelligence can show severe language
deficits.
2. People with impaired intelligence can have
normal language skills.
•
Williams syndrome characterized by metal
retardation but skillful use of language.
Evolution and Physiology of
Language
• Evidence suggesting language evolved as an
extra brain module specialization includes:
– Language acquisition device is a built in
mechanism for acquiring language.
• Evidence comes from the ease at which most
children develop language.
– Chomsky (1980) further suggests the poverty of
stimulus argument: children do not hear many
examples of some of the grammatical structures
they acquire.
Evolution and Physiology of
Language
• Most researchers agree that humans have a
specially evolved “something” that enables
them to learn language easily.
– Certain brain areas are indeed necessary for
language.
– But same areas are also necessary for other
tasks (memory and music perception).
• Exactly how humans evolved language is
unknown but is perhaps due to the pressure
for social interaction.
Evolution and Physiology of
Language
• Research suggests a critical period for
learning language.
• Learning a 2nd language differs with of age:
– Children are better at learning pronunciation
and unfamiliar aspects of grammar.
• No sharp cutoff for 2nd language learning:
– Adults learn a second-language vocabulary
better.
Evolution and Physiology of
Language
• Rare cases of children not exposed to
language indicates limited ability to learn
language later.
• Deaf children unable to learn spoken
language and not given the opportunity to
learn sign language while young reveals:
– Little development of skill at any language
later.
– Early exposure to some language increases
ability to learn another language later.
Evolution
Anatomical
control of breathing
(aquatic theory)
Developmental
1-word holophrase
2-word slot grammar
native language grammar
Animal models
Chimpanzee - gesture
Parrot - oral
Animal models
Parrot - oral
1 9 . Langua ge and Lat eralizat ion
Language
Evolut ion
Anato mical
Deve lopment al
Animal models
Neurology
Broca’s area
Wernicke’s area
Language a nd m emory
Lat eralizat ion
Anat om y
Funct ion
Evolution and Physiology of
Language
• Most knowledge of brain mechanisms of
language come from the study of people
with brain damage:
– Broca’s area is a part of the frontal lobe of the
left cerebral cortex near the motor cortex.
• Damage results in some language disability.
– Aphasia refers to a condition in which there is
severe language impairment.
Evolution and Physiology of
Language
• Broca’s aphasia/nonfluent aphasia refers to serious
impairment in language production, usually due
to brain damage.
• Omission of most pronouns, prepositions,
conjunctions, auxiliary verbs, tense and number
endings during speech production.
• People with Broca's aphasia have trouble
understanding the same kinds of words they omit
(prepositions and conjunctions).
Evolution and Physiology of
Language
• Broca’s aphasia is usually accompanied by
comprehension deficits when:
– The sentence meaning depends on prepositions,
word endings or unusual word order.
– Sentence structure is complicated.
• Broca’s area thus seems to be critical for the
understanding of some, but not all, aspects
of grammar.
Fig. 14-15, p. 435
fMRI records of speech
Fig. 14-16, p. 436
Evolution and Physiology of
Language
• Wernicke’s area is an area of the brain located near
the auditory part of the cerebral cortex.
• Wernicke’s aphasia is characterized by the
impaired ability to remember the names of objects
and also impaired language comprehension.
– Sometimes called “fluent aphasia” because the person
can still speak smoothly.
• Recognition of items is often not impaired; ability
to find word is impaired.
Evolution and Physiology of
Language
• Typical characteristics of Wernicke’s
aphasia include:
1. Articulate speech / fluent speech except with
pauses to find the right word.
2. Difficulty finding the right word - anomia
refers to the difficulty recalling the name of
objects.
3. Poor language comprehension - difficulty
understanding spoken and written speech
(especially nouns and verbs).
Table 14-1, p. 438
Lateralization of Function
• Lateralization of function refers to the idea
that each hemisphere of the brain is
specialized for different functions.
• Each hemispheres controls the contralateral
(opposite) side of the body.
– Example: skin receptors and muscles mainly on
the right side of the body.
– Each hemisphere sees the opposite side of the
world.
Lateralization of Function
• The left and right hemisphere exchange
information primarily through a set of axons
called the corpus callosum.
• Other areas that exchange information
include:
– The anterior commissure.
– The hippocampal commissure.
– A few other small commissures.
• Information crosses to the other hemisphere
with only a brief delay.
Fig. 14-2, p. 418
Lateralization of Function
• The two hemispheres are not mirror images of
each other.
• Division of labor between the two hemispheres is
known as lateralization.
– In most humans the left side is specialized for language.
• The corpus callosum allows each hemisphere of
the brain access to information from both sides.
Lateralization of Function
• Each hemisphere of the brain gets input from the
opposite half of the visual world.
• The visual field is what is visible at any moment.
• Light from the right half of the visual field shines
into the left half of both retinas.
• Light from the left visual field shines onto the
right half of both retinas.
Lateralization of Function
• The left half of each retina connects to the left
hemisphere.
• The right half of each retina connects to the right
hemisphere.
• Half of the axons from each eye cross to the
opposite side of the brain at the optic chiasm.
• The auditory system is arranged differently in that
each ear sends the information to both sides of the
brain.
Fig. 14-3a, p. 419
Lateralization of Function
• Damage to the corpus callosum interferes with the
exchange of information between hemispheres.
• Epilepsy is a condition characterized by repeated
episodes of excessive synchronized neural activity.
– Mainly due to decreased release of the inhibitory
neurotransmitter GABA.
• Physicians once cut the corpus callosum to
prevent the seizure from spreading to the opposite
side of the body.
Lateralization of Function
• People who have undergone surgery to the
corpus callosum are referred to as splitbrain people.
• Spit brain people maintain normal intellect
and motivation but they tend to:
– Use hands independently in a way others
cannot.
– Respond differently to stimuli presented to only
one side of the body.
Fig. 14-4, p. 420
Lateralization of Function
• Sperry (1974) revealed subtle behavioral
differences for spilt brain people.
• Because the left side of the brain is dominant for
language in most people, most split brain people:
– Have difficulty naming objects briefly viewed in the
left visual field.
• A small amount of information can still be
transferred via several smaller commissures.
Fig. 14-5, p. 422
Lateralization of Function
• Immediately after surgery, each hemisphere
can only quickly and accurately respond to
information that reaches it directly.
– Smaller commissures allow a slower response.
• The brain later learns use the smaller
connections:
• Difficulty integrating information between
both remains.
Fig. 14-6, p. 423
Lateralization of Function
• Right hemisphere is better at perceiving emotions.
• Damage to parts of the right hemisphere causes
difficulty perceiving other’s emotions, failure to
understand humor and sarcasm, and a monotone
voice.
• Left hemisphere damage increases ability to
accurately judge emotion.
– Associated with decreased interference from the left
hemispheres.
Lateralization of Function
• The right hemisphere is also better at
comprehending spatial relationships.
• In general, the left hemisphere seems to
focus more on visual details, and the right
hemisphere focuses more on visual patterns.
Lateralization of Function
• Some anatomical differences exist between the
hemispheres of the brain.
• The planum temporale is an area of the temporal
cortex that is larger in the left hemisphere in 65%
of people.
– Difference are slightly greater for people who are
strongly right handed.
• MRI studies indicate that the a big difference in
the ratio of left to right planum temporale is
related to increased language performance.
Fig. 14-9, p. 425
Lateralization of Function
• Damage to left hemisphere often results in
language deficiencies.
• Left side seems to be specialized for
language from the very beginning in most
people.
• The corpus callosum matures gradually
through the first 5 to 10 years.
– Thus, young children have difficulty comparing
information from the left and right hand.
Lateralization of Function
• Being born with a condition where the corpus
callosum does not completely develop results in
extra development of the following:
– Anterior commissure - connects the anterior parts of the
cerebral cortex.
– Hippocampal commissure - connects the left and right
hippocampus.
• Allows performance on some tasks that differs
from split-brain people.
Lateralization of Function
• The left hemisphere is dominant for speech
in 95% of right-handed people.
• Most left-handers have left-hemisphere or
mixed-dominance for speech.
– Few people have strong right hemisphere
dominance.
Lateralization of Function
• Recovery of language after damage to the brain
varies.
• Age affects extent of recovery.
– Brain is more plastic at an early age.
• Right hemisphere reorganizes to serve some of the
left-hemisphere function.
Lateralization of Function
• Rasmussen’s encephalopathy is a rare condition in
which the immune system initially attacks the glia
and then the neurons of one hemispheres of the
brain.
– Usually begins in childhood or adolescence.
• Surgeons eventually remove or disconnect the side
of the damaged brain.
• Language recovers slowly but substantially.
– Slow deterioration allows the other side of the brain to
compensate and reorganize.
Lateralization of Function
• Language recovery after brain damage is also
influenced by how language was initially
lateralized for the given person.
• Individuals with partial representation of language
in both hemispheres recover better than those with
language dominance in one hemisphere.