Reason for crossed projections in the nervous system?

[J. A. Kiernan]

In article <47lg75$h6v at fremont.ohsu.edu> Matt Jones <jonesmat at ohsu.edu> writes:
>From: Matt Jones <jonesmat at ohsu.edu>
>Subject: Re: Reason for crossed projections in the nervous system?
>Date: 6 Nov 1995 17:21:41 GMT

>In article <rambis.815616371 at isum1.iastate.edu> Paul L Pearson,
>rambis at iastate.edu writes:
>>Can anyone give me a solid hypothesis for why the left side of the body
>>is controlled by the right side of the brain and vice versa?  This

>Early swimming animals evolved crossed projections from the visual system
>to the motor systems, so that an object perceived on one side of the body
>would cause contraction of the muscles on the opposite side, leading to a
>swimming movement away from the object (escape).

   Cajal thought it was to compensate for optical inversion of the images
   projected onto the retinas.  See "Recollections of my Life" pp. 470-475.

                                     John A. Kiernan
                                     Department of Anatomy
                                     Univ. of Western Ontario
                                     LONDON, Canada  N6A 5C1
                                     e-mail: kiernan at uwo.ca