How did this come about?

X

Xenu

BBS Whore
Registered Senior Member
Here's something that I've wondered for a long time and can never get a straight answer on:

Does anyone know why the brain and body are setup in a contralateral way (for the most part)? For example the left brain controls the right hand, right visual field etc. ; the right brain controls the left hand, visual field etc.

What advantage does this have? It seems to be more of a disadvantage.
 
I have a good idea!

If early humans displayed "handed-ness" like we modern humans do, maybe..

If they were right handed, and thwacked themselves in the head (it'd prolly be the right side) and then poof they cant use their right side of the body anymore!

So the brain switched itself so if the right-handed protohuman smacked his noggin on the right side..it would affect his left side.

Nevermind, forget everything i wrote above..
 
Xenu ...

Interesting question. Surprised I hadn't wondered about it.

Hmm ... How about other mammals? Are they set up the same way?

Take care, and thanks.
 
To my knowledge, all mammals (which have separate hemispheres at least) are set up contralaterally.

-Xenu
 
Originally posted by NenarTronian
I have a good idea!

If early humans displayed "handed-ness" like we modern humans do, maybe..

If they were right handed, and thwacked themselves in the head (it'd prolly be the right side) and then poof they cant use their right side of the body anymore!

So the brain switched itself so if the right-handed protohuman smacked his noggin on the right side..it would affect his left side.

Nevermind, forget everything i wrote above..
Click to expand...

Actually, what you said parallels what I thought to be a disadvantage. If a mammal were to damage one half of the body (say it gets crushed under a rock or trampled by an elephant, etc.) Then the animal would be completely incapacitated, neither side would be able to move too well.

-Xenu
 
Hmm ...

That being the case, it not being unique to our species, I'm really baffled.

But then, what could be the disadvantage?

Nothing comes to mind that way either.

Weird.

Thanks ... I think :confused:
 
The big disadvantage to a contralateral system is conduction time. You have that much more axon to travel to reach where it needs to go. It's not as efficient.

This extra time wouldn't matter to much with an axon traveling a large distance, say your foot. But look at something like the ear. The temporal cortex, where most of the auditory info is processed, is right next to the ear. But most of the auditory nerve of the right ear travels all the way across the brain to the left temporal cortex rather than just a few centimeters away at the right temporal cortex. Vice versa with the left ear.
 
I'm not sure whether conduction time is such a big disadvantage. Sensory impulses (well, most of them, anyway) are not sent directly to the cortex. The auditory impulse is relayed (in the middle of the brain) before it is distributed to the auditory cortex. (This goes for tactile, visual, etc. impulses as well.) So conduction time doesn't have to be the big disadvantage of a contralatertal system. At least there is no disadvantage when it comes to information processing in general.
 
Alright, I oversimplified it. My mistake.

Yes, the auditory nerve goes to the mid-brain before the cortex. But before it goes to the cortex it crosses over at the Superior Olivary Complex (which is in the medulla). The crossing distance is much shorter than say from cortex to cortex, but still there is an increase of conduction time to travel that distance (and an increase in axon length, needing more room), which may or may not be important (note though, a fraction of a second can mean life or death in the wild). What mystifies me is that going from the Ventral cochlear nucleus (where the auditory nerve enters the brain) to the Superior Olivary Complexes (SOC), the major path is always the one that crosses to the contralateral SOC. There are projections to the same-side SOC too, but there aren't nearly as many. Why couldn't the major projection be the ipsilateral side and a minor projection to the contralateral? It would be slightly more efficient.

The one thing that I've learned from physiology is that nature isn't lazy or sloppy. Everything within the body has a reason or once had a reason for being there.

Still puzzled, I'm not looking for die-hard proof (because I'm sure there aren't any), any hypotheses are welcome.

-Xenu
 
Xenu

Momma says aligators are ornery coz they got all them big teeth and no toothbrush...
 
Here's a picture of what I'm talking about above to help those who aren't familiar with what I'm talking about. Look at the bottom section, this is the medulla. Keep in mind, that the size has been enlarged and the distance isn't as great as depicted (in relation to the top picture). They also don't distinguish between major and minor pathways.

http://www-ece.rice.edu/~dhj/pathway.html
 
Re: Xenu

Originally posted by Adam
Momma says aligators are ornery coz they got all them big teeth and no toothbrush...
Click to expand...

Dude, I have no idea what you're talking about with this. But it's funny though :p
 
It's from the movie The Waterboy. Uneducated chap in psych class tries to tell the professor why aligators are particularly rough around the edges.
 
I see, thanks. Never saw that one. Not a big Adam Sandler fan.

*ducks to avoid hurled axes whizzing by his head*
 
Xenu ...

Took a look at the site. Interesting, but it only addressed horizontal
sound source location. Considering that it appears to be a fairly recent
text, I'm surprised that vertical sound source location was not discusssed.

Take care.

Edited for typo.
 
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hehehe

Maybe God was bored and inexperienced at the time of creation, and unfortunately, He had prepared the head separately from the body, and then He had to go and lose the glue gun (probably landed somewhere in the middle of the Amazon, that's why it's so hot and sticky), and then He just got tired of it and jammed the head on and twisted it 180 degrees like a bottle cap so the little wires and thingies got attached then twisted, and that's why the left is connected to the right and vice versa.

Wanna hear my story about why there are 2 genders and not just one hermaphroditic individual? *lol* just kidding, i still have to make that one up :D
 
Re: Xenu ...

Originally posted by Chagur
Took a look at the site. Interesting, but it only addressed horizontal
sound source location. Considering that it appears to be a fairly recent
text, I'm surprised that vertical sound source location was not discusssed.

Take care.

Edited for typo.
Click to expand...

I guess I wasn't looking at the site, only the picture, because it was almost exactly what I was looking at when I was describing it earlier.

But you bring up an interesting point. I don't remember learning about vertical sound source either, only on a horizontal plane. I imagine, it works the same way as you determine if something is in front/behind you - echo patterns from the shape of the pinnae.

-Xenu
 
Good one gifted.

I think the thing here is, it doesn't matter which way you process info in your brain. Ever how you become used to it is how it is done.

How many here could explain and give directions to someone else how to move an arm so that the one person hearing the explaination and directions could follow them and result in their understanding and moving the arm? It is an intutive process, biological in nature, that all have in common with a few notable exceptions.
 
Xenu ...

Ran across a study many years ago that addressed the subject.
Unfortunately, it was so long ago, almost fifty years, I can't
remember the source (I was a psych. major at the time).

Essentially: The outer ear structure acts as a micro-delay circuit that
permits us to determine vertical orientation, peculiar to primates.

Included an interesting experiment: Blindfolded, determine the location
of a sound source with and without the outer ear distorted.
Horizontal location unafftected, vertical lost either in part or totally.

Take care.

Edit: Just remembered: Horizontal location is mildly affected if the
sound source is behind the subject.
 
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