"Karl Self" <karl.self at gmx.net> wrote in message
news:9dkml6$insp0$1 at ID-34153.news.dfncis.de...
> Thanks for your speedy reply. As always, new knowledge spawns new
> questions ... (see below).
>> "James Teo" <james at teoth.fsnet.co.uk> wrote:
> ...
> > Nobody knows. Good luck for your nobel prize.
>> Ta, but I can't right now. I'm too busy trying to win me the Field
> Medal and few Pullitzers.
>> ...
> > All sensory input crossover in humans before entering the hemispheres.
>> I hope I do not sound smart - arsed asking this: so vision and
hearing
> are cross wired, but I guess taste isn't because it is not stereoscopic
(or
> do we have two tongue hemispheres)? What about nostrils -- is smell
> stereoscopic (can we smell left from right, and if not, what is the point
of
> having two nostrils rather than one (other than aesthetic reasons, maybe),
> and are the nostrils cross - wired as well?
> Sorry to be so inflationary in my questioning. I promise to be
equally
> inflationary in my appreciation of any forthcoming answers.
The vertebrate brain is crossed like you describe, but invertebrate brains
are usually wired "correctly" -- the left side of the body is connected to
the left side of the CNS. There is really no point to the crossover -- it
probably is an anomaly of the developmental genes controlling the
bilateral body, distinguishing anterior from posterior, dorsal from ventral,
and left from right. Somewhere along the line, the left-right axis in the
nervous system got mismatched.
I am not sure whether taste and smell are crossed -- I believe the
special "visceral" senses are wired somewhat differently from the
special "somatic" ones. But there are indeed many animals that
can accurately locate food sources by detecting the direction of
taste and smell. The "distance" sense of smell is more complex
because odors are carried by air or water currents. Often, on
detecting an attractive weak odor, an animal will respond simply
by swimming or flying upstream. But then when the odor is strong
enough, many animals can detect the gradient and definitely move
towards to source. Similarly, many animals use the contact
chemical sense (the barbels of fish, for example) to explore their
environment and to locate food.
