2120: Brain Hemispheres
Title text: Neurologically speaking, the LEFT hand is actually the one at the end of the RIGHT arm.
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As a general rule, each cerebral hemisphere (half of the brain) innervates (feeds/supplies/controls) the contralateral (opposite side) portion of the body. So things on the left half of the body are controlled by the right side of the brain and vice-versa. As previously noted however, this is simply a rough approximation. Biology is complicated, and as with most biology "rules" there are exceptions.
A notable exception are the cranial nerves; some do not decussate (cross over) as would be predicted from the rule above and directly innervate the ipsilateral (same side) side (eg abducens CN6). And of course, many cranial nerves innervate both ipsilateral and contralateral sides. This phenomenon is often seen, when everything is working properly, in things like the pupillary reflex (when you shine a bright light in one eye, both eyes' pupils constrict)
While the motor and sensation aspects of nerve innervation have been relatively well-established from studies, experiments, and dissections, (mostly through knockout(what happens to function if I damage/remove this part of the brain?) or stimulation studies) there is probably always going to be an exception, as you might imagine. Any number of factors may cause deviation from the normal physiology: trauma, disease, congenital birth defects, brain plasticity, etc.
With less concrete aspects of human brain function, such as logic, emotion, language processing, and creativity, establishing which brain hemisphere has control is obviously more complicated. Because a lot of these are higher order functions (these are things you tend to learn, develop, and obtain as you grow into an adult from a neonate), establishing which hemisphere has control of which function are obviously more complicated. Due again to brain plasticity or other factors, different developing brains may grow to wire control of these functions differently. So while studies have established which hemisphere is more likely to be involved with which function (eg left with language processing), again mostly through knockout studies, these generalizations are not necessarily true for every individual.
Randall spoofs these by suggesting that the right brain instead controls the upper torso, while the left brain still controls the right side. The product of this partitioning in two dimensions gives four areas of the human body (upper left, upper right, lower left, lower right) and would eventually suggest that your left leg moves independently of your brain. To explain the areas of the body controlled by both halves of the brain, Randall declares those sections "disputed," echoing a note added on maps that must display a border which is part of a territorial dispute. This suggests that the halves of your brain fight for control of the region, and is also described similarly to two countries disputing territory. Alternatively, he states there would be cooperative shared control (= Dual control) like in an airplane, where the pilot and the copilot both can control the plane with their respective yoke or stick at any time. His (fun) theory would explain, why most people are more skilled with their hands than their feet and with their right side than their left.
The title text further confuses the aspects of this decussation. The fact[dubious] that hands are an exception in neurology might be a confusion based to the common argument explaining the actual exceptions mentioned above, that a strictly divided control over body halfes would make coordinated tasks with both hands close to impossible.
|This transcript is incomplete. Please help editing it! Thanks.|
- [Cueball is shown with the right half of his brain (on the viewer's left) colored in orange and the left half (on the viewer's right) in iris blue. An iris blue box is overlaid over the right half of the body (on the viewer's left), and an orange box is overlaid over the top half. The boxes are overlapping in a greenish color on the upper right quarter of the body (on the viewer's left).]
- Neuroscience Fact:
- [An arrow pointing to the iris blue rectangle on top with the text above:]
- The left half of the brain actually controls the right half of the body...
- [An arrow pointing to the orange rectangle at the right, the text reads:]
- ...while the right half of the brain actually controls the top half of the body.
- [An arrow pointing to the overlapping area (the top left body from the viewers perspective) with the text below:]
- Disputed/dual control
- [An arrow pointing to Cueball's left leg area (on the viewer's right), not highlighted by any color, and the text is:]
- This leg is fully autonomous
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