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NESC 3227 (19)
Kim Good (19)

January 10th, 2013.docx

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NESC 3227
Kim Good

January 10th, 2013 January-10-13 1:06 PM Laterality/Cerebral Asymmetry  Often used interchangeably, but really not the same  Cerebral asymmetry has to do more with structure than function  While laterality has more to do with functional differences Body and brain have two halves  When we're talking about structure, we mean anatomical construction o There's a fair bit of symmetry from right to left  Functional refers to behaviour Why study laterality?  Does brain structure dictate body structure? Or vice versa? If you look at the brain  Left and right hemispheres appear anatomically as mirror images of each other  All the primary sensory areas in the brain tend to be fairly symmetrical across hemispheres  As you move up to areas of more complex controls, functionality and structure both begin to differ between hemispheres o Such as language being processed mainly in left hemisphere, and music and spatial stuff in right hemisphere Structural brain asymmetries; what do we measure?  Firs t thing you can look at are changes in size or shape (Gross anatomy changes)  Or you can look more finely at the cells that make up these hemispheres to see if there's any difference o You can do this post mortem o Or you can use neuroimaging techniques, although this doesn't really hit the cellular level yet  How to measure? o By volume or weight are acceptable ways Gross asymmetries in brain structure  Right frontal lobe extends more anteriorly  But the left occipital lobe extends farther posteriorly  *but it's not clear if there's more brain volume on one side, or if this is just spatial displacement  What does this asymmetry mean?  Has it been linked to any functional changes? Gross cerebral asymmetries  Lateral fissure has a steeper slope on the right side  The planum temporale is larger on the left  The heschl's gyri is larger on the right size Replicable anatomical asymmetries: Planum Temporale  Very important for language  Much larger on the left than the right  It's part of Wernicke's area  Heschl's gyri is more than double the size on the right compared to the left Problems with measurement  Like foot measurement example in textbook  How the measurement is taken can be very important and cause a great deal in variability of results between studies  In the foot example, there was a failure to replicate results due to different methodologies of measurement Solving the replication problem  How do we ensure the findings we get are correct? o We use multiple methods of measurement and only if they say the same thing can we ensure accuracy of our measurement findings  Such as post mortem, MRI studying, and counting number of neurons are examples of different methods MRI confirms some structural brain asymmetries in living humans  They looked at morphometric studies in healthy subjects and confirmed the results of other measurements Post-mortem brain anatomy  A very labour intensive process as you need to remove the brain from the skull without damaging, slice the sections you want  Defining the regions of the brain in cadavers can prove to be very difficult as there are very few landmarks that are consistent across subjects o As well as experimenter bias (where does olfactory bulb end, and olfactory tract start?) Advantages of MRI technology  There are fully automated software programs that can do things like outline the hippocampus for you  It can examine the whole brain to allow for viewing of many areas at once  You can superimpose images of other brains on top of each other, and stretch/shrink the images to fit the other ones  You can also do mirror images of a brain in order to conduct left-right comparisons of brain hemispheres Watkins, Paus et al., (2001)  Used MRI to compare measurements to that of previous pathological research studies, and both did find asym
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