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Lecture 9

Lecture 9.doc

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University of Toronto Scarborough

Lecture 9 Left Hemisphere - in LH damage caused by bullet wounds 100% had some aphasic (language) symptoms - 30% would show some recovery of varying degrees => all left-handed or ambidextrous individuals that were able to recover => least amount of recovery in right-handed individuals - LH must be involved in language bc 100% showed some form of damage - RH damage caused by bullet wounds showed very few language problems, and rarely lead to a form of aphasia => those who did show aphasic ppl were all left handed or ambidextrous => most of the patients showed recovery from the language problems - right handed ppl w a bullet wound to the RH – no aphasic symptoms => in right handed ppl language is located in the LH - in left handed ppl language is bilaterally – represented in both sides => damage to either side disrupts language Language development: - in children under the age of 5, damage to either side has equal probability of inducing aphasic symptoms => some language found on both sides of the brain in children - in addition, 100% of children will show some degree of recovery - either side can take over the function of language after brain damage => language is not yet lateralized - over development language slowly becomes lateralized to one side => when children have brain damage on one side of the brain, language is found on the other side of the brain - some neuropsychologists suggest that left handed ppl are the result of brain damage in childhood - brain is very plastic during dev’t and loses plasticity as it matures => especially around 2-3 – children cant remember anything before that - in infants brain damage can be treated by removal of the damaged parts of the brain => the remaining parts of the brain take over *at birth both hemispheres are capable of language acquisition => LH seems to become more dominant for language with maturity Acollosal patients: - patients born w/o a corpus callosum have language on both sides in the adult brain - during dev’t LH actively suppresses the RH => bc in acollosal patients language remains on both sides - if hemispheres can’t communicate, some language stays on the RH => active suppression when LH can communicate w RH, or if LH is damage and can’t suppress, RH will remain w language ability - LH suppression not as active in left-handed ppl, bc some language remains on RH Anatomical differences: Planim temporale: primary language area in temporal lobe; larger, more convoluted and heavier on the left side, by about 1/3 => suggests LH speech area is more equipped anatomically to handle language bc larger in size - in other apes left temporal lobe was also larger and heavier than the right – not just in humans => also true in other animals that communicate, such as birds – vocalization controlled by the LH - appears that genetic predisposition for animals that communicate to have vocalization to lateralize to the LH => also true for left handed ppl – anatomical adv for LH, even though language on both sides - also seen in infants, and fetuses at 10-31 weeks of gestation => larger temporal lobes not caused by experience of speaking – genetic/evolutionary predisposition Normal humans: - hippocampus buried deep inside the temporal lobe – may need to be removed to stop seizures in epilepsy (common area for seizures) - sodium amytal test done before surgery – injected into one side or the other, and takes a couple minutes before it reaches the whole brain 1 => one side of the brain put to sleep, the person counts backwards and watch as one side becomes paralyzed (opposite side of the brain injected) => if language is located on the left side, the person stops counting as the left side becomes p
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