Lecture NotesLecture 9:Lateralization
(Left Hemisphere = Speech, Right Hemisphere = Music/Spatial)1
•Most of the brain lateralization information was gathered through wars (WWII)
•They realized that different brain damages caused different symptoms (some can't speak etc)
•These information are all based on adults (soldiers).
Research in Brain Damages in Adults (WW2 Soldiers):
Left Hemisphere Damaged Soldiers
•100% of these patients show some aphasic symptoms (language problems).
•approximately 30% of these patients showed SOME sort of recoveries, and these were either
LEFT handed individuals or they're Ambidextrous (both-handed).
•The least amount of recovery was in the RIGHT handed patients.
•Thus they concluded that left hemisphere is responsible for language.
Right Hemisphere Damaged Soldiers
•These soldiers showed very few language problems, and rarely did it lead to some form of
•The patients that did show aphasic symptoms, were all LEFT handed or ambidextrous.
•Most of these left handed patients showed recovery from the language problems.
•Thus they suggested that Language is bilaterally represented (Language is on both hemispheres)
•Also, they suggested that if you're right handed, language is on your left hemisphere. If you're
left handed, language is on both sides (thus if you get damaged on either sides of the brain, you
will have some sort of language problems. However, the good part is that if one side of the brain
is damaged, the other side can take over and slowly learn, thus might slowly recover).
Research in Brain Damages in Children (Under the age of 5)
•Damage to EITHER side of the brain has equal probability of inducing aphasic symptoms.
•However, 100% kids show some degree of recovery.
•Thus, some language is found on both sides of the infant’s brain, also, language is not yet
lateralized in these young infants. Moreover, over time, through development, language is slowly
lateralized to left side of the brain.
•Because the development of the brain in infants is extremely plastic (neuroplasticity), if the
infants got a heavily damaged hemisphere of the brain, it's better to just take the whole thing out
rather than leave it in there (seizures). Amazingly, the other side of the brain will take complete
control, and hardly any problems are spotted within the child.
Acallosal patients (Patients born without a carpus callosum)
•These patients as adults have language components on both hemisphere of the brain.
•Thus we conclude that when we were first born, both hemispheres of our brain are capable of
learning language. However as we mature and begin to develop language, the left hemisphere
becomes dominant over language, and it becomes more competent in it. Also, the overly
development of the left hemisphere actively suppresses the right hemisphere.
So... what is so special about left hemisphere?
•People did anatomical study on the left hemisphere of the brain looked into the dorsal,