Lateralization Flashcards
Cerebral commissures
connect the two halves of the brain
Corpus Collusum
Aphasia
deficit in language comprehension or production due to brain damage
usually on left
Broca’s area
in left inferior prefrontal cortex
expression and speech
combines sounds into words
Damage of broca results in
Broca’s aphasia
unable to speak fluidly
lots of nouns
Sodium amytal test
Anesthetize one and check for language function
Dichotic listening
Report more digits heard by the dominant half
Functional brain imaging for lateralization tests
fMRI or PET used to see which half is active when doing a language test
Left hemisphere is speech dominant in which “handers?”
almost all dextrals - right-handers most sinistrals
left-handers
what happens when you cut the corpus collosum?
each hemisphere functions independently
Apraxia
difficulty performing movements when asked to do so out of context, also a consequence of damage on the left.
Dual foci of attention
split-brain hemispheres can search for target item in array faster than intact controls
one hemisphere will suffice if task is…
easy
extra hemisphere is needed to process a what kind of task?
If task is difficult
Z lens
Can be used to assess each hemisphere’s understanding of spoken instructions by limiting essential visual information to one side of brain
What kind of info somehow passes between hemispheres?
emotional information
Right hemisphere superiority
Spatial ability
Emotion
Musical ability
Some memory tasks
Left hemisphere superiority
Language
superior in controlling ipsilateral movement
Planum temporale
Wernicke’s area
Heschl’s gyrus
Primary auditory cortex
Frontal operculum
Broca’s area
All theories propose that it’s better to have brain areas that have …..
similar functions be in the same hemisphere
Analytic-synthetic theory
Two modes of thinking :
analytic (LH)
synthetic (RH)
Vague and essentially untestable
“The darling of pop psychology”
Motor theory
Left controls fine movements – speech is just a category of fine movement
Left damage may produce speech and motor deficits
Linguistic theory
Primary role of left hemisphere is language
Evolution of Lateralization of Function:
Some nonhuman primates:
Tend to use their right hand for communicative gestures, particularly when vocalizing
Have right hemisphere superiority for facial expression and identity, suggesting that evolution of laterality preceded evolution of hominids
Language localization
place within the hemisphere of language circuitry
Arcuate fasciculus connects to the…
Broca’s and Wernicke’s areas
Left angular gyrus is posterior to the…
Wernicke’s area
damage to the Arcuate fasciculus
causes conduction aphasia (inability to repeat words just heard)
Comprehension and speech normal
damage to the Left angular gyrus
causes alexia (inability to read) and agraphia (inability to write)
Comprehension of language-related visual input
Surgery that destroys only Broca’s area
has no lasting effects on speech
Removal of much of Wernicke’s area
has no lasting effects on speech
Activity in brain areas for specific cognitive processes . . .
underlie language-related behaviors
have functions independent of language
are likely to be small, widely distributed, and specialized
Bevalier’s fMRI study of reading was about
cortical involvement in reading
Reading sentences versus control periods (strings of consonants)
Areas of activity were tiny and spread out
Active areas varied between subjects and trials
Activity was widespread
is there language in the brain beyond the wernicke and geschwin model?
YES!
Dyslexia
reading difficulties not due to some other deficit (e.g., vision, intelligence)
Developmental dyslexia
– apparent when learning to read
Heritability estimate = 50%, More common in boys than girls
Various subtle visual, auditory, and motor deficits are commonly seen
Genetic component – yet the disorder is also influenced by culture
Acquired dyslexia
Due to brain damage
Relatively rare
(deep dyslexia) extensive damage to left-hemisphere language areas
Developmental Dyslexia: Causes and Neural Mechanisms
Perhaps a deficit of phonological processing rather than sensorimotor processing
Brain differences identified, but none seems to play a role in the disorder
Multiple types of developmental dyslexia – possibly multiple causes
Lexical
using stored information about words
Surface dyslexia
lexical procedure lost.
Can’t recognize words.
loss of visual recognition of words (cannot “look and say”)
Surface: “steek” for “steak”
Phonetic
sounding out
Deep dyslexia
Phonetic procedure lost. Can’t sound out unfamiliar words
loss of ability to “sound out” unfamiliar words or “nonwords”
Deep: “hen” for “chicken”
How is it that lexical abilities are spared?
Lexical abilities may be housed in left language areas that are spared
Lexical abilities may be mediated by the right hemisphere
Evidence for both exists
