How does my brain locate my hand in space?

  • #1

Main Question or Discussion Point

If I close my eyes (so as to remove my sense of sight) and spread my fingers so they do not touch (so as to remove sense of feeling) and then move my hand around, I still have a sense of where in space it is located. How is my brain figuring out the location of my hand under these conditions?
 

Answers and Replies

  • #2
Evo
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If I close my eyes (so as to remove my sense of sight) and spread my fingers so they do not touch (so as to remove sense of feeling) and then move my hand around, I still have a sense of where in space it is located. How is my brain figuring out the location of my hand under these conditions?
From the nerve signals sent from the hand. You don't need sight to sense your body.
 
  • #3
What are the nerve's being stimulated by?/What information are they transmitting? Are they transmitting information about how tense my various muscles are and then from that information my brain is calculating the orientation and extension of my arm and hence the location of my hand?
 
  • #4
Pythagorean
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Yup, exactly, little mechanosensors in the muscle spindle measure how much your muscles have stretched and report it to the nervous system, increasing frequency of firing with intensity of muscle stretch.

By some feat of neural computation, your parietal lobes use this somatosensory information (along with other information from your different sensory systems, such as your vestibular system, which detects the motion of fluid in your brain and your head's orientation with respect to gravity) to put together a picture of your body's configuration in space. Of course, having seen 3D space with your eyes your whole life and having echo-located on sounds with your ears (assuming you have functioning eyes and ears), there's probably a lot of extra help from an informed imagination.
 
  • #5
atyy
Science Advisor
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  • #6
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Yes, proprioception. It is the incredibly important sense that most don't realize they have or need. The few people who have completely lost their sense of proprioception have had their lives devastated. Oliver Sacks tells the story of one woman who lost it in his book "The Man Who Mistook His Wife For a Hat", in chapter 3, "The Disembodied Lady".

Due to Multiple Sclerosis, my Brother-in-Law has lost the proprioception in his feet. He can't tell where they are except by looking at them. He has to walk staring at his feet.
 
  • #7
I wonder whether it is possible to read the signals from these nerves (by placing a electrode or something on your arm) and interpret them so as to be able to track your hand.
 
  • #8
Ryan_m_b
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I wonder whether it is possible to read the signals from these nerves (by placing a electrode or something on your arm) and interpret them so as to be able to track your hand.
Do you mean for people who have dysfunctional proprioception? A less complicated and risky method could be to devise mechanical devices worn on the knees, elbows, shoulders and hips that apply pressure to different areas of the limb on the basis of how extended the joint is. Overtime perhaps patients will adapt to this; I've read a Sacks case wherein the patient could no longer balance. They improvised a small spirit level attached to his glasses so that he could tell if he was standing straight. After a lot of practice he could walk again and the action became automatic.
 

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