On 10 Feb 2004, Pollak, Edward wrote:
I had 2 questions from students the other day that I could not answer hopefully you folks can help.
1) This is an old one to which I've never found a satisfactory answer: Is there an adaptive significance to the contralateral
organization of the brain. If so, what is it? Or is it just a
peculiarity of neural development.
Braitenberg (1994) describes an answer provided by Ramon y Cajal.
Cajal's account was that crossing originated with the visual system. Cajal suggested that the crossing was done to correct for the image inversion that happens with our camera-like eyes. The argument goes like this. The left and right halves of the visual field end up on the retina as inverted and left-right reversed. If these two retinal images were projected by uncrossed fibers onto a common receiving surface then there would be a midline discontinuity in the mapping of the visual field. The crossing of fibers at the chiasm was to correct for the issue.
Braitenberg then goes on to show that this is not the only method to correct for this issue. Other fiber weaving patterns can accomplish the same result.
Ken
--------------------------------------------------------------- Kenneth M. Steele, Ph.D. [EMAIL PROTECTED] Department of Psychology http://www.psych.appstate.edu Appalachian State University Boone, NC 28608 USA ---------------------------------------------------------------
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