very interesting.

--- Meir Weiss <[log in to unmask]> wrote:

> How does the brain know what the right hand is
> doing?
> EurekAlert! Wed, 22 Mar 2006 6:04 AM PST
> A new experiment has shed more light on the
> multi-decade debate about how the
> brain knows where limbs are without looking at them.
> 
> 
>
http://www.eurekalert.org/pub_releases/2006-03/bpl-hdt032206.php
> 
>  Public release date: 22-Mar-2006
> [ Print Article | E-mail Article | Close Window ]
> 
> Contact: Lucy Mansfield
> [log in to unmask]
> 44-186-547-6241
> Blackwell Publishing Ltd. 
> 
> How does the brain know what the right hand is
> doing?
> 
> A new experiment has shed more light on the
> multi-decade debate about how the
> brain knows where limbs are without looking at them.
> 
> You don't have to watch your legs and feet when you
> walk. Your brain knows where
> they are. For decades scientists have debated two
> options for how the brain
> achieves this:
> 
> (1) the outflow hypothesis says that the brain
> monitors signals it sends to the
> muscles telling them how strongly to contract, and
> uses this to predict where
> the limb has moved to;
> (2) the inflow hypothesis suggests that the brain
> relies on information from
> sensors within tissues that say how far a limb has
> moved.
> 
> While there has been plenty of evidence that inflow
> plays a role, no one before
> has been able to show definitively that outflow is
> also important.
> 
> Now research just published in The Journal of
> Physiology provides evidence that
> outflow is involved. Working at the Prince of Wales
> Medical Research Institute
> in Sydney, the Australian research team asked
> subjects to sit at a bench and
> place their right hand through a screen so they
> couldn't see it. The hand was
> clamped so that the researchers could move it, but
> the subjects could only push
> against a fixed plate. The researchers then moved
> the hand and the subjects had
> to say which way it was pointing. The researchers
> then asked the subjects to
> push against the plate, and say where they thought
> the hand had moved to. The
> researchers inflated a cuff around the arm, cutting
> off blood flow and
> temporarily paralysing and anaesthetising the arm.
> They then repeated the tests.
> 
> Before the cuff was inflated, the subjects
> accurately indicated where their hand
> was pointing, both when they were resting and when
> they were pushing against the
> plate. After the arm was paralysed and
> anaesthetised, the subjects were unable
> to detect when researchers moved their hand, but
> incorrectly thought that they
> were still able to move it themselves when they
> tried to push against the plate.
> 
> 'The fact that the person thought they had changed
> the position of their
> paralysed hand, even though they hadn't, shows that
> the perception of limb
> position is at least partly driven by outflow
> commands going to the muscles.
> There were no incoming signals from receptors, so
> this cannot have been
> responsible for the illusion,' says Dr Janet Taylor,
> one of the authors of the
> paper.
> 
> The experiment provides a new and intriguing
> illusion that sheds light on how we
> learn to move accurately, as well as indicating why
> some people who have had
> limbs amputated still feel as if they can move their
> 'phantom' limb. 
> 
> 
> ###
> 
> 
> 
> 
>
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> 
>   
> 


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