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B65 Lec 9 Laterality.docx

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Michael Inzlicht

B65 LECTURE # 9: Laterality (Localization and Specialization) Historical/General Overview • First laterality obvs came from war (the injuries that soldiers experienced, ex. Bullet wound on the left or right side) • LEFT hemi wound for adults: o 100% show some aphasic (lang problems) symptoms o Approx 30% show recovery, these people were mostly left-handed or ambidextrous o The least amount of recovery was in right-handed individuals (because language is predominantly in left brain when you’re right-handed). o Right hemi is also capable of lang in left-handed individuals meaning not all fxn is lost if left hemi is wounded o Theorized that ambidextrous are actually just lefties who are forced to learn right  We can test ambidextrous by getting someone to look through a telescope (which eye), throw a ball, get them to check if a clock is ticking (which ear) • RIGHT hemi wound for adults: o Most showed a few and minor aphasic symptoms, but rarely full-blown aphasia o Those that DID show aphasic problems were always the lefties/ambidextrous but they show very good recovery o Thus, lefties clearly have language on both sides so wounds on left or right will affect them but it will always only be mild o but righties have more severe issues for left hemi, but nearly no issues for right hemi • either hemi damage for kids (less than 5 y.o) has an equal probability of affecting lang o thus we conclude that lang is on both sides at that point, unlike an adult o 100% of kids who suffer brain damage show recovery o Therefore, kids are kind of like lefties o Child’s brain is not yet fully lateralized o Over time, brain becomes more and more lateralized (beginning at 5 y.o  teen years) o Lateralization primarily occurs in right-handed individuals, but lefties have more split on both sides o Child can even recover from an entire side of the brain being removed because they still have so much plasticity and lack of lateralization Acollosal People: • Born without a corpus callosum • Towns in Quebec with a fairly high percentage of people who genetically have this • They have language on both sides of brain (even in right-handed adults) • We conclude that left hemi is better at lang and so it will actively suppress right side • But if there is no corpus callosum to let the hemis communicate, the left hemi won’t do this! Children w/ early extensive brain damage: • Language is almost always on opposite side of brain as the damage -it’s actually been suggested that lefties may have had some small amount of brain damage when they were younger and that’s why their brain never lateralized Anatomy of Left Brain: • Left temporal lobe, mainly the planum temporale, is the primary language area • in left brain, planum temporale is heavier by 1/3 and more convoluted than same structure on the right • left-specialization is found to be a very genetic, primitive thing that has been around for ages • other species present the same left-specialization • therefore, it’s not just a lifetime of use that causes left brain to be specialized for language. Left is just inherently more capable to begin with. • Between 10 to 20 week of gestation, we already show left temporal being larg
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