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Jessica Krueger's picture

Kind of off topic...

When Professor Grobstein was elaborating upon the concept of proprioception, he asked us if we had to look at ourselves to make sure we were standing up straight. The example he gave was of a man unable to maintain postural control because of his loss of proprioception, so the question kind of makes sense. However, postural control and remaining upright is actually a fairly intricate task requiring more input from the environment than just "self-awareness."

In fact three systems are required to keep your head over your shoulders, and your shoulders over you knees. Balance is maintained by information provided by the visual system, the proprioceptive system and the vestibular system of the inner ear. (1) Proprioception and vision have already been briefly discussed in class, so I'm going to spend a little time discussing the vestibular system.

The vestibulum, along with the organs of hearing, houses the two organs responsible for detecting where we are in space: the semicircular canals (which detect rotation) and the otoliths (which detect linear translation and position relative to gravity).(2) We each have a set of three canals on either side of our heads (mirroring the three dimensions of our world) which work in a "push-pull" system, simultaneously inhibiting the other side when one is activated. The otoliths, each composed of an utricle and saccule, which function by detecting the displacement of hearing "ear crystals" suspended in in gel as we speed up or slow down ou turn our heads upside down. This system is also heavily reliant/bound up in the visual system, with both processes driving eachother to orient the body towards relevant events.(3)

So the man in the article Professor Grobstein presented to us presumably had an intact vestibular-visual pathway, because when he looked at himself he was able to translate the visual and vestibular inputs into postural control. Had someone with a vestibular pathology, like Meniere's disease, been asked to complete a similar task when denied proprioceptive information, they presumably would not have been able to. Even with body-awareness input, sufferers of Meniere's disease experience varying degrees of vertigo and have diffuculty maintaining balance (I know this from living with a person who has been diagnosed with Meniere's disease). So I guess this is just to say that perhaps there are more sensory modalities or modality combinations to consider when trying to translate from neurology to behavior.

1. http://en.wikipedia.org/wiki/Equilibrioception

2. http://www.physpharm.fmd.uwo.ca/undergrad/sensesweb/L10Balance/L10Balance.swf

3. http://www.bio-medicine.org/biology-definition/Vestibular_system/

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