evolutionary benefit of the brain's neural crossover

[gforcepdx]

I am beginning my undergraduate studies for a Masters in Social Work and am taking psychology 201. This has us studying the basic structures of the mind and my reading is leading me to questions not addressed yet within our course work.

 

Has anyone established an evolutionary benefit of the brain's neural crossover effect? Everything provides a benefit it would seem, so what theory's have been put forward for the left brain controlling the right hand and so on?

 

Also, how far down the evolutionary track does this trait go ?

 

I know that they have discovered many animals literally sleep with one eye open (dolphins, ducks) and that this has to do with hemispheric isolation. That by having both sides of the brain operate independently, one side can rest while the other side remains aware of predators. This separation provides a powerful benefit. But why the cross over?

[forufes]

well i'm not sure you should be looking at it from a "benifit" point of view, even that usually helps, rather, shouldn't it be something like this: why would the first ever being with a brain mutated with a crossover reproduce better?

 

and i don't know

 

but maybe because if the right side of the body gets damaged you can still control it with the brain that's on the other undamaged side (but then you can't control the undamaged side of your body cuz it's controlling brain is damaged)?

 

waaaiit a second.. the ear sack thingy with the fluid inside used for balance, it's directly connected to the brain, no? so maybe it's easier or more accurate to sense imbalance of a body if you're connected to it from afar and not ON it, like the tail blade in helicopters, it's small, but due to the long arm it keeps the main body pretty steady relatively effortlessly, as opposed to it being so close to the main body, cuz then you're magnifying any "turbulence" or imbalances for easier detection AND correction..

 

so it could be the same, the sack sensor can sense imbalance in one side of the body better when it's actually on the other side, and it may have been more convenient(supposedly there's no such thing in evolution) to switch the whole two brain halves then switch the sacks and keep them connected to their halves on the other side..

 

haha, i'm a genius.

 

nice thread btw.

[iNow]

What you're referring to is called "decussation" (also, as trasnslateration). My understanding is that decussated arrangements in the cortex and body are very robust, and that it has an advantage in minimizing errors in neural wiring during development. Errors in wiring are relatively common in organisms with simpler wiring schemes on the same side of the body. Given that, organisms with wiring problems were less likely to reproduce than organisms without wiring problems, and the decussated arrangement of neural architecture was advantageous evolutionarily and selected for through the generations.

 

 

I might be wrong. It's been a few years since I read about this stuff, and I'm still working on my first cup of coffee today.

[Mr Skeptic]

I recall making a very simple automaton, consisting of two photodetectors and two motors, one on each side of the body. With the signal from each photodetector used to regulate the speed of the motor on the opposite side of the body (brighter=faster), the automaton would move toward the light. I wonder if our ancestor was a light-seeking animal?

[forufes]

With the signal from each photodetector used to regulate the speed of the motor on the opposite side of the body

but why not the opposite?

i.e each photodetector regulates the wheels' speed on its side(brighter==slower), it would be as easy as modifying one line of code, and the performance would be the same[?]

[J.C.MacSwell]

The explanation I was given was that given a blow to the head from the side, it would leave the body more able to defend the side from which the attack came, since the opposite side had control of it.

 

I was quite young when I heard that, and never really questioned it.

[Skye]

There are lots of theories for both motor and sensory decussation. One of the oldest, by Ramon y Cajal in the 19th century, is that it accounts for image inversion by lenses in the eyes. Others developed from this are similar to Mr Skeptic's automaton in that the decussation could be used to lump visual information processing and motor control on one side of the brain. There's also the robustness idea that pretty new.

 

Here's a recent paper that providesmore background: http://arxiv.org/PS_cache/arxiv/pdf/1003/1003.1872v1.pdf

[Charlatan]

I am beginning my undergraduate studies for a Masters in Social Work and am taking psychology 201. This has us studying the basic structures of the mind and my reading is leading me to questions not addressed yet within our course work.

 

Has anyone established an evolutionary benefit of the brain's neural crossover effect? Everything provides a benefit it would seem, so what theory's have been put forward for the left brain controlling the right hand and so on?

 

Also, how far down the evolutionary track does this trait go ?

 

I know that they have discovered many animals literally sleep with one eye open (dolphins, ducks) and that this has to do with hemispheric isolation. That by having both sides of the brain operate independently, one side can rest while the other side remains aware of predators. This separation provides a powerful benefit. But why the cross over?

 

The brain crosses over because it needs the signals to join at some point for communication based on electrical impulses, and, that means that they relay information onto the other side for synthesis and coordination, based on dual actions of using two hands at once. The information may then allow the brain's 'operating system' side to control the ohter side. Take a look at my diagram:

 

 

[left brain half]<->[right brain half]

\ /

[actions] \ / [processing]

\ /

[meeting] - makes other side of the body act aswell...

/ \

/ \

[left side] [right side]

 

I suggest the right half of the brain acts as if it were ram for a computer. It allows for the actions or dominant left side to use it's space to make temporary bonus processing. If the left half of your brain enacts things, then the right side should open the door for 'fresh ideas', or fresh input. We therefore need both halves to work properly.

 

The thing is memories are not stored in the brain, as they are electrical impulses and they will travle around the body. The brain is there to regulate a lot of impulses around the brain's area, using it to store signals and acts as a hub to relate impulses, many of them, at once.

 

Just a little statement, I am a creationist, so don't ask me to go into that Dawkins nonsense, please.

[CharonY]

I realize that it can be fun making things up, however if one has not the slightest idea how it works one should not post in a way that suggests that it is anything but mere fantasy.

Thanks.I realize that it can be fun making things up, however if one has not the slightest idea how it works one should not post in a way that suggests that it is anything but mere fantasy.

Thanks.

 

As regarding to the benefit , it is a misconception that everything has to be of benefit in an evolutionary way. Sometimes when a developmental path has been selected, there are some side issues that come with it that are not necessarily beneficial. At least part of it has to do with the bilateral symmetry of our body development. But crossing the signal itself also provides important information as exemplified in stereoscopic vision, which requires crossing at the optic chiasma. Also I think that the way the view field is split it actually reduces the reaction time by reducing the time necessary to reach the motor area of the respective body side without having to pass the pons. But I would have to draw it to recall it in more detail (it has been a long while since I last had neurobiology other than on the molecular level).

 

Note that we are actually talking about three things here.

1) why is there a bilateral separation and why is it set up like as it is

2) what are the diverse cross-overs good for

3) what is the evolutionary history of it (note that I am not specifically arguing benefits here)

Edited May 5, 2010 by CharonY

[ewmon]

Since we're talking about why/how decussation evolved, where in evolution did it begin and is it universal among animals? Mammals? Yes. Marsupials? Reptiles? Arthropods? Cephalopods? Etc.