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Zachariah Campbell

CEREBRAL DOMINANCE/LATERALITY and the NEUROPSYCHOLOGY of LANGUAGE Lateralization- two hemispheres have different functions -most ppl are right-handed thus, -language is almost exclusively on the LEFT hemisphere of brain -for those who are left-handed/ambidextrous -language is BI-laterally located Note: Ambidextrous ppl are neurologically LEFT handed and were probably forced to use right-hand History -most early research gathered from war survivors who were injured in only one side of brain (RIGHT or LEFT) -prior to injury they were normal adults over age of 20 -if bullet wound was in left hemisphere, 100% of patients showed some aphasic (language/speech) symptoms -BUT, about 30% of these show some recovery of language -of these 30% (the ppl who shoed recovery), all were either left-handed or ambidextrous -least amount of recovery was in right-handed ppl Conclusion: -Some language is in left hemisphere for ALL ppl -Right-handed ppl didn’t recover, therefore ALL language is in LEFT hemisphere -Left-handed or ambidextrous ppl did recover somewhat therefore although there is language in left hemisphere, some language ability occurs in RIGHT hemisphere. -if bullet wound was in right hemisphere, essentially NONE showed aphasic symptoms -those who did show some symptoms were LEFT-handed/Ambidextrous (this makes sense b/c they have language in both hemispheres) -all right-handed ppl showed no symptoms -AGAIN, virtually all of the LEFT-handed/Ambidextrous ppl showed some recovery Development, Children, and Language -in children under age of 5, damage to either hemisphere has equal probability of producing aphasic symptoms -BUT, 100% of these children show large recovery, no matter their handedness (this is not like adults- see above) -this means both hemispheres are involved in language and the development of language -furthermore, by the recovery evidence, both hemispheres (the remaining non-damaged parts) are capable of language (in kids with severe epilepsy or scar tissue, we sometimes remove a whole hemisphere but child develops surprisingly normally) -acollosal patients are born without a corpus callosum -seems to be genetic -interestingly, language is on BOTH hemispheres of brain in these patients -children with early extensive brain damage to the LEFT hemisphere, have language shift to opposite side of brain (the RIGHT hemisphere) AND it has been suggested that the child’s handedness shifts as well! Conclusions: -early in development, both sides of brain are capable of language -BUT over time in right-handed ppl, seems that left hemisphere becomes more competent and takes over language (AND seems to suppress right hemi in terms of language-see below)) -Why does the left always seem to take over? b/c for some reason it is dominant/better suited to handle language -Why do acallosal patients have language in BOTH hemispheres? -this seems to suggest that the left hemisphere, in normal ppl, SUPRESSES the right hemisphere -the communication b/w the two hemispheres, in normal ppl, is a suppression msg from left to right hemisphere -this also explains why children with damage to the left get language localized in right its b/c left hemisphere can’t send suppression msg, so right hemisphere can take over Evolution (trys to explain why left is dominant for language) In humans, planum temporale- is language area in left and right temporal lobe -it is larger, more convoluted, and heavier in left hemi than in right by one-third BUT, maybe it’s b/c of experience and usage or right side of body (see research below that disproves this notion) -this was also true in other primates (great apes) as well even tho they don’t have speech -left hemisphere is also larger in song birds -seems as tho this is evolutionary/genetic and not just growth by experience/usage -we also see this larger left hemi in LEFT-handed ppl th st -we also see this larger left hemi in new borns between 10 and 31 week of gestation anatomical prediposition Classic Sodium Amitol Expt’s (on epileptic patients) -person comes in with epilepsy and meds are not working even at high doses -at this point they need surgery to remove the focus of the seizures which is usually in the temporal lobe (which as we know, also contains speech) -first we need to localize the place that needs removal (which temporal in which hemisphere) b/c we don’t want to remove both sides and we also want to know which side speech is localized in the person SO: -we give them a sodium amitol injectio
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