Question: Why is it that the left side of our body is controlled by the right side of our brain and the right side of our body is controlled by the left side of our brain.

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  1. OK, my answer to this is kind of long winded but the basic story is that our brains are very ordered and there is an exact map of the outside world stored in the structure of the brain itself-this is called a topographic map.
    So, every body part has a special spot in your brain, every part of what you see or hear etc. This means that the cells that respond to these senses and the axons and nerve fibres they send out all have to be in a special topographic order as well.
    The reason why things are crossed over is because it helps our brain to coordinate both sides of our bodies to respond to the cues in our environment. When you move your hand, you are actually coordinating a number of different brain areas and neurons from both sides of your body including visual input, balance, the position of your body in space etc. So if everything was on the one side and stayed on that side, you wouldn’t be able to very easily coordinate all this information.
    Complicated, I know….


  2. Awesome answer, Kristyn!

    I was going to go for the obvious answer; because the nervebundles cross over, never even realized it helps with coordination!


  3. This is an excellent question!

    So your brain is divided into two hemispheres, the left and right, and these are connected by a structure called the corpus callosum, which is a large bundle of nerves which link the two hemispheres.

    Kristyn already answered this really, but I’ll add a couple of cool things about lateralisation:

    – Your language is located in the left hemisphere, in a place called the temporal lobe
    – Spatial awareness is located in the right hemisphere, in the parietal lobe

    We can also see what happens to people when the two hemispheres can’t communicate, which happens sometimes if people have to have brain surgery (called a Corpus callosotomy). This can cause problems with following oral instructions – for example if you are told to do something with your left hand, your left hemisphere (language hemisphere) processes the speech, but it’s the right hemisphere which controls this movement – if the two hemispheres can’t communicate, it’s really difficult to follow these sorts of instructions!

    There have been amusing anecdotes about people in this situation whose body tries to communicate to the other hemisphere, for example in the above situation, the right hand might start slapping the left hand to try to tell it to do something, but the person won’t really know why it’s doing it!!