Transcript Lateralization & The Split Brain - U

Lateralization of Language
ch.16 (cont’d)
and
Biopsychology of Memory
ch. 11
Lateralization
and
Cortical Localization of
Language
Ch. 16 (cont’d)
Outline
• Differences Between the Left and Right Hemispheres
• Broca’s Area
• Wernicke’s Area
Differences Between
The Left and Right Hemispheres
• Language is the most lateralized of all
abilities; the left-hemisphere is better than
the right at most language-related tasks
• however, the right hemisphere proved to
be able to understand single written and
spoken words (video); also righthemisphere detects prosody and discourse
Differences Between
The Left and Right Hemispheres
• The right hemisphere proved better than
the left at a variety of tasks involving
spatial ability, emotional stimuli and
musical tasks
• LH hippocampus is associated with verbal
memory and RH hippocampus is associated
with spatial memory
Differences Between
The Left and Right Hemispheres
• The two hemispheres seem to engage different
types of memory processing; LH attempts to place
its experience in a larger context (relation of
parts that make up the whole), while the RH
attends strictly to the Gestalt perceptual
characteristics of the stimulus (either the parts or
whole but not relation between)
• This is usually termed analytical (LH) versus
holistic (RH)
Differences Between
The Left and Right Hemispheres
• Thus the RH should not be regarded as the
minor hemisphere; it has different abilities,
not less important ones
Differences Between
The Left and Right Hemispheres
• There are also anatomical asymmetries in
the human brain; for example the planum
temporale and frontal operculum (language
related areas) are larger in LH
• However, Heschl’s gyrus (also language
related) in larger in RH
Differences Between
The Left and Right Hemispheres
• (not in book) left-handers seem to have
symmetrical planum temporales, suffer less
severely from LH aphasia, and suffer more
severely from RH aphasia
• This suggests left-handers may have a more
diffuse representation of language and is
evident in differential strategies in sentence
processing
Differences Between
The Left and Right Hemispheres
• For example in priming studies, when the
target word is LILY, right-handers are
quicker at deciding that it as a word if they
are primed with the word ROSE, where as
left-handers are quicker at deciding if
primed with the word POND
Differences Between
The Left and Right Hemispheres
• LILY and ROSE fit same syntactic
templates
– i.e., The ___ bloomed. The ___ is a flower.
• LILY and POND are associated in real
world semantic representation
Three Theories of
Cerebral Asymmetry
• Analytic-synthetic theory
• Motor theory
• Linguistic theory
Analytic-Synthetic Theory
• Suggests that there are two fundamentally
different modes of thinking, an analytic mode
(LH) and synthetic mode (RH), and that the
neural circuitry for each is fundamentally different
• LH (pieces of the whole) operates in logical,
sequential, analytic fashion
• RH (the whole) makes immediate, overall
synthetic judgments
Analytic-Synthetic Theory
• Experienced musicians are left-hemisphere
dominant for processing music
Motor Theory
• Posits that LH is specialized for fine motor
movement of which speech is but one example
• Two lines of evidence:
– Lesions of the LH disrupt facial movements more than
do RH lesions, even when they are not related to speech
– Degree of disruption of nonverbal facial movements is
positively correlated with the degree of aphasia
Linguistic Theory
• Based on the view that the primary function of the
LH is language; this is based on studies of deaf
people who communicate using ASL; this ability
is lost if these people suffer damage to the LH,
even when they are able to make the movements
required
• (or is this just showing ASL is a language, or that
language is highly analytical or that ASL requires
fine motor movements of the hand like speech
does of the mouth/tongue?)
Broca’s Area
• Inferior left prefrontal area in left
hemisphere
• Damage leads to deficits primarily in
speech production (problems with
expression) and also grammatical
comprehension
Wernicke’s Area
• Left posterior temporal area, just posterior to
the primary auditory cortex
• Damage leads to deficits to semantic language
comprehension (problems with reception) and
speech is semantically incomprehensible, despite
having correct grammar, rhythm and intonation
(word salad)
• Broca’s area
(Broadmann’s area
44 and 45)
• Wernicke’s area
(narrowly defined
as BA22 but can
also describe BA37,
39 and 40).
Conduction Aphasia
• Damage to white matter (heavily
myelinated) tract connecting Broca’s and
Wernicke’s areas called the arcuate
fasciculus
• Comprehension and spontaneous speech are
intact but patient not able to repeat words
they have just heard
Arcuate fasciculus
Arcuate fasciculus
Conduction Aphasia
• However, conduction aphasics (temporoparietal
lesions) are a heterogeneous group in terms of
impairment (some more Broca’s aphasic - like,
some Wernicke’s aphasic - like) suggesting arcuate
fasciculus may not be the only underlying
structure
Perisylvian language networks of the
human brain (Catani, et al., 2005)
• Newly discovered but evolutionarily older
structure in addition to the classical arcuate
fasciculus
– parallel and lateral to classical arcuate fasciculus
– Connects “Geschwind’s territory” (inferior parietal cortex that
receives multimodal inputs important for semantics; BA39 and 40)
to classical language areas (Broca’s and Wernicke’s areas)
– Rudimentary form of this network exists in the brain of other
primates (macaque monkey)
Perisylvian language networks of the
human brain (Catani, et al., 2005)
Arcuate fasciculus (unique to humans; long segment; medial)
and other network (anterior segment and posterior segment)
Perisylvian language networks of the
human brain (Catani, et al., 2005)
• Corroborates neuropsychological evidence
for different types of conduction aphasics
– Classical conduction aphasia (long segment
lesion; failure in automatic repetition)
– Transcortical aphasia (anterior segment
lesion; failure to vocalize semantic content)
– Sensory aphasia (posterior segment lesion;
failure of auditory semantic comprehension)
• Broca’s area
(Broadmann’s area
44 and 45)
• Wernicke’s area
(narrowly defined
as BA22 but can
also describe BA37,
39 and 40).
Alexia
• Damage to the left angular gyrus (area of
left temporal and parietal cortex just
posterior to Wernicke’s; BA39)
• Inability to read despite intact language
comprehension and production
Agraphia
• Also due to damage to the left angular
gyrus
• Inability to write despite intact language
comprehension and production
• Involvement of LAG in alexia and agraphia
show its responsible for language related
visual input
Broca’s Aphasic Video
(shown in class)
Wernicke-Geshwind Model
• Seven components in Left hemisphere:
primary visual cortex, angular gyrus,
primary auditory cortex, Wernicke’s area,
arucate fasciculus, Broca’s area, and
primary motor cortex
Responding to a heard question
• Primary auditory cortex to Wernicke’s area where
comprehended
• To respond, concept generated in Wernicke’s area,
goes via arcuate fasciculus to Broca’s area, then to
primary motor cortex and articulatory areas (face,
lip, and tongue muscles, voice box, and muscles
assoicated with lungs)
• (animation in class)
Reading aloud
• Primary visual cortex to left angular gyrus,
which transmits visual code to auditory
code
• Then to Wernicke’s area to arcuate
fasciculus to Broca’s to primary motor
cortex to articulatory areas
• (animation in class)
Evidence against W-G Model
• Damage to these boundaries has little lasting effect
on language
• Damage to other brain areas can produce aphasia
• Broca’s and Wernicke’s aphasia are rarely “pure” aphasia is both receptive and expressive
• Major individual differences for cortical
localization for language
Cognitive Neuroscience
Approach to Language
• Cannot perform lesion studies because
humans are only known species with
language
• Use Cognitive Neuroscience (brain imaging
like PET and fMRI) to study relation of
brain and language
Cognitive Neuroscience
Approach to Language
(1) Each of of the components in W-G model
can be broken down further into
constituent cognitive processes
(1) Phonological analysis (sounds)
(2) Grammatical analysis (structure)
(3) Semantic analysis (meaning)
Cognitive Neuroscience
Approach to Language
(2) Areas of brain involved in language are
not solely dedicated to language; many of
the constituent cognitive processes also play
roles in other behavior
Example - some areas involved in short-term
memory and visual pattern recognition are
involved in reading, too
Cognitive Neuroscience
Approach to Language
(3) W-G model assumes that brain areas
involved in language are large,
circumscribed, and homogenous but
Cognitive Neuroscience assumes they are
small, widely distributed, and specialized
Dyslexia and Cognitive
Neuroscience
• Dyslexia is pathological difficulty in
reading, does not result from general visual,
motor, or intellectual deficits
• Developmental dyslexia- apparent in
childhood
• Acquired dyslexia - damage in individuals
who were already capable of reading
Developmental Dyslexia
(1) Differences between brains of dyslexic
and non-dyslexic readers have been
reported, however none seems to play a
critical role
Example - dyslexics do not display the
asymmetry of the planum temporale
Developmental Dyslexia
(2) Several types of dylexias and thus likely to
have different causes and brain areas
susceptible
Developmental Dyslexia
(3) Difficult to determine cause-and-effect of
brain abnormalities
Are these abnormalities the cause of dylexia
or the result of lack of reading experience
(brain develops differently as a result of
different experience)?
Acquired Dyslexia
• Two strategies for reading aloud:
– Lexical procedure - based on specific stored
information that has been acquired about
written words - looks at it, recognizes it and
says it (yacht, aisle)
– Phonetic procedure - looks at words,
recognizes letters, sounds them out and says
word (fish, river, glass)
Acquired Dyslexia
• Surface Dyslexia - patients lose ability to to
pronounce words based on the specific memories
of the words (they lose their lexical procedure)
• Can pronounce non-words - wug
Example: can pronoun words consistent with rules
( fish, river, or glass) but can’t pronounce unusual
words (have, lose, and steak are like cave, hose,
and beak)
Acquired Dyslexia
• Deep Dyslexia - patients lose ability to
apply common rules of pronunciation ( they
lose their phonetic procedure)
• Can’t pronounce non-words
Example: can say phonetically unusual words
like aisle and yacht but cannot pronounce
rule-consistent words like fish, river, or
glass
Acquired Dyslexia
• Where are lexical and phonetic processes in
the brain?
• Deep dyslexia (lose phonetic procedure)
due to damage in LH
• Surface dyslexia (lose lexical) due to partial
LH damage or RH damage
The Neuropsychology
of Memory
Ch. 11
Outline
• Review of memory terms
• Amnesic Effects of Bilateral Medial
Temporal Lobectomy
• The case of H.M.
Learning vs. Memory
• Learning deals with how experience
changes the brain and memory refers to how
these changes are stored and later retrieved
• We have learned much about the neural
mechanisms of memory by studying
amnesic patients
Types of Memory
• Episodic memory - explicit and declarative
• Semantic memory - explicit and nondeclarative
• Procedural memory - implicit and nondeclarative
Amnesic Effects of Bilateral
Medial Temporal Lobectomy
• H.M. suffered from severe, intractable
epilepsy; he seemed to have epileptic foci in
both medial temporal lobes
• A bilateral medial temporal lobectomy
was prescribed for H.M.; this included the
removal of the hippocampus and
amygdala
Amnesic Effects of Bilateral
Medial Temporal Lobectomy
• In some respects, the operation was a
success: H.M.’s convulsions were reduced
in severity and frequency and his IQ
increased from about 104 to 118,
however…
Amnesic Effects of Bilateral
Medial Temporal Lobectomy
• H.M. suffered from devastating amnesia as
a result of his operation
H.M.’s Memory Deficits
• H.M. has minor retrograde amnesia (can’t
remember events before his surgery) for
events of the 2 years preceding the surgery
• He has normal memory for remote events
and normal short-term memory (his digit
span is about 6)
H.M.’s Memory Deficits
• However, he cannot form long-term
memories for events that occurred after his
surgery
• This is called anterograde amnesia. For
example, he has no memory of his new
home, his new job, or new friends
H.M.’s Memory Deficits
• At first, it was assumed that H.M. could not
form long-term memories at all, but
objective testing revealed that H.M. can
demonstrate his retention of certain types of
tasks by his improved performance on them,
although he has no conscious recollection
of previously practicing them
H.M.’s Memory Deficits
• H.M.’s deficits can be described in terms of
his performance on six objective tests of
memory:
H.M.’s Memory Deficits
– Digit Span +1 Test: after 25 trials with the
same series of digits, he could do only 7 digits,
just one more than his normal memory span
– Block-Tapping Memory-Span Test: his blocktapping memory-span was normal; but he could
not extend it, even by one, when the same
sequence was repeated for 12 trials
H.M.’s Memory Deficits
– Mirror-Drawing Test: he displayed substantial
savings with no conscious recall of previous
practice
– Rotary-Pursuit Test: he displayed substantial
savings with no conscious recall of previous
practice
H.M.’s Memory Deficits
• Incomplete-Picture Test: after seeing 5 sets of 20
line drawings of varying completeness, he
displayed substantial savings with no conscious
recall of the drawings
• Pavlovian Conditioning: tones and a puff of air
to the eye were presented to H.M.; he blinked in
response; two years later he retained this
conditioned pairing almost perfectly although he
had no conscious awareness of his previous
training
H.M.’s Memory Deficits
• H.M.’s case had the following significant
influences on the study of memory:
– It showed that the medial temporal lobes are
important to mnemonic functions
– It challenged the view that mnemonic functions
are diffusely represented throughout the brain
H.M.’s Memory Deficits
– It renewed efforts to related specific brain
structures to specific mnemonic processes
– It supported the theory that there is a different
mode of storage for short-term and long-term
memories
– H.M.’s case provided the first evidence that
implicit memory could survive in the absence
of explicit memory
Medial Temporal Lobe Amnesia
• H.M.’s ability to form implicit, but not
explicit, long-term memories is often seen
in cases of medial temporal lobe amnesia,
as well as other amnesic disorders
Medial Temporal Lobe Amnesia
• Repetition priming tests are used to assess implicit
memory; patients are shown a list of words and sometime
later they are shown a series of word fragments and asked
to complete the words
• Amnesic patients do as well on this task as control
subjects, even though they do not remember ever seeing
the original list of words
Medial Temporal Lobe Amnesia
• Recent research has suggested that
problems with episodic memory (memories
for the events of one’s own life) are more
common than problems with semantic
memory (memories for general facts or
information) in patients suffering from
medial temporal lobe amnesia
Medial Temporal Lobe Amnesia
• The fact that implicit are intact while
explicit memories are compromised in
patients suffering from MTL amnesia raises
the question
“Why do we have 2 memory systems… one
conscious, and the other unconscious?”
Medial Temporal Lobe Amnesia
• The answer seems to be differential
flexibility; implicit memories do not
transfer well to different contexts, whereas
explicit memories can