IUBio

Cross - Wired Eyes

maxwell mmmaxwell at hotmail.com
Sun May 13 02:50:42 EST 2001


James Teo <james at teoth.fsnet.co.uk> wrote in message news:3afdd7ab.1471976 at news.freeserve.net...
> On Sun, 13 May 2001 01:17:35 +0200, "Karl Self" <karl.self at gmx.net>
> wrote:
> >I know that in humans, the eyes are cross wired to the brain, i. e. the left eye is connected to the right brain hemisphere and vice versa.  Myquestions:-  why is this so?
> 
> Nobody knows. Good luck for your nobel prize.
> 
> >-  am i right in thinking that only the eyes, and no other organs (e. g.
> >ears) are "wired up" in this manner?
> 
> All sensory input crossover in humans before entering the hemispheres.

No. Temporal hemifields of retina do NOT decussate--
thus left brain sees right half-field of visual space: left half of left retina does not decussate (cross over), while left half of right retina (nasal hemifield) DOES cross over. This *partial* decussation is typical of primates, while in birds and reptiles the crossing-over is complete, which if you consider the lateral placement of the eyes, is unsurprising.

I could discuss this in much greater depth, but please read a primer
first:

http://luna.cas.usf.edu/~husband/evolve/avc5vpth.htm

Later..

-maxwell



> 
> >-  are there any animals in which eyes and brain hemispheres are not cross -wired?
> 
> Don't know any, other than leeches, but then it is debatable whether
> or not they have a brain or just a ganglion.




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