Kitchen Science - Rising Arms

This week's Kitchen Science requires no equipment - just you, your brain and your arms!...
25 October 2009

Interview with 

Ben Valsler & Meera Senthilingam


Ben -   I'm sorry to say that this week, Dave Ansell is actually in bed with a flu, leaving me to handle Kitchen Science all on my own. But luckily, I'll be joined later on by Meera Senthilingam who will help me demonstrate an old experiment that I've known about since I was very little where you can fool your brain into making your body do something very strange. It's a really simple one to try out at home, so do please give it a go. All you need is a doorway and your arms. So, find the doorway, stand in the middle of the doorway, facing in to the room and drop your arms down by your side. Then press the backs of your hand doorframe and push and push and push and push. You need to push for about a minute. It'll start to hurt, it'll feel very uncomfortable, but you need to keep going. And after a minute, all you need to do is step forward and relax your arms.


Arm muscles - front, superficialBen -   Welcome back to Kitchen Science.  Today, I'm having to cope without Dave but I do have a very willing victim.  Sorry, volunteer, Meera Senthilingam.  Hello, Meera.

Meera -   Hello.

Ben -   Now, you've seen this experiment done before, haven't you?

Meera -   Yeah, but a while ago.

Ben -   So then you might have an idea to what's happening, but hopefully will still be a bit of a surprise.  So if you could come with me over to this doorway then we can get you set up.

Meera -   Okay.

Ben -   So, you need to stand in the doorway, facing into the room.  Now this door is actually quite narrow which is kind of perfect for us because you don't want to have to lift your arms too much.  If your door is a lot wider then it might work better to get somebody to put their foot behind the door and just make the right size space between the door frame and the door itself.  But here, there's maybe 6 inches maybe either side of your hand, so that's pretty much perfect.  You feel comfortable standing in the doorway?

Meera -   Yeah.  As comfortable as you can be in a doorway.

Ben -   And now the next thing to do is put your arms down by your sides and then just  and place the backs of your hands against the doorway.  So they're level with your hips and pushing out on the door.

Meera -   Okay.

Ben -   Now, here's the tricky bit.  What I need you to do now is to push outwards on the door frame, as hard as you're comfortable with and you're going to have to do this for about a minute.  So, when you're ready, start pushing.

Meera -   Okay.

Ben -   Well I can see from your face that you are genuinely putting some effort in here.  Now the thing with this is initially doesn't feel too bad.  You're just pushing out against the doorway and nothing really feels like its happening.  But then after, probably about this much time, it actually starts to get quite uncomfortable.  But don't stop.  Do keep pushing.  How are you feeling?

Meera -   Uncomfortable, but I'm trying.  I'm trying.  I'm concentrating.

Ben -   Well we still have to go for a little bit longer yet so I may as well distract you by explaining what's going on in your brain.  Now your brain sends messages to different groups of muscles, telling some to relax and some to contract in order to create the movement that you need.  Right now, certain muscle groups will be contracting as hard as they can to try and push out against the door.  But obviously, they're not doing very well unless you have a very flimsy house.  In which case, you may have broken your own doorway.  How are you feeling now?

Meera -   It's quite painful actually and is it okay that my arms are actually shaking a little bit?

Ben -   The shaking I think is just evidence that you're really putting in the effort to it.  I think you've probably had long enough now.  So what I need you to do, when I say go, I need you to step forward and just relax your arms completely.  So, are you ready?

Meera -   Okay.

Ben -   Go.

[Meera's arms mysteriously rise up from her sides - without her trying to do so]

Meera -   My arms!  Okay.  That was quite cool.

Ben -   And you do look a bit like you're sleep walking now as your arms appear to be stuck out in front of you.  But how does it feel?

Meera -   It feels completely normal.  Like it doesn't feel that my arms have raised at all.  It just feels that they're just dangling and I can actually just happen to see them in front of my face.

Ben -   And normally, if were to hold your arms out in front of you, it would actually take some effort.  But does this position feel like you're totally relaxed and this is where your arms are supposed to be?

Meera -   Yeah.  Basically, as if I was in a swimming pool or something and my hands were just sitting on top of the water.  That's what it feels like.

Ben -   Well, what's actually happening to your arms has, until very recently, been a bit of a mystery.  Back in the 1920s, people knew about this experiment but they assumed that it was all to do with the spinal cord.  Because there are nerve clusters that control the length of muscle and so they assume that the spine was involved.  But now, in a very new paper that came out in September in the journal Brain Research, Amy Parkinson and her colleagues have actually done this very experiment inside a brain scanner to have a look at what's going on.  Now they compared scans of people making this movement on purpose, to people doing it exactly how we've just done, pressing against something for a while and then this involuntary movement happening afterwards.

If people had been right in the '20s and it was a spinal cord only issue, then you'd see very little brain activity or certainly nothing significant compared to normal.  But what they found was significant brain activity in the areas that were concerned with making and planning movements.  And they found this activity just before the movement happened.  So this wasn't a response to the fact that your arm was moving of its own accord.  This really was the effect that made it happen.  They also did find some activity in the brain that happened after the movement and this suggested that that was a response to the fact that your arm was involuntarily moving. 

One of the bits they did find quite a lot of activity in is called the cerebellum.  Now this is what's responsible for motor learning and error corrections.  So it must have learned while you were pushing out.  That your arm was apparently supposed to be shorter than it really is and that's why the muscles contracted and your arms rose up at their own accord.

This is very similar to an experiment that we did a little while ago on The Naked Scientists where we put special prismatic glasses on.  These shift your vision 10 degrees to one side and then when you try and throw and catch a ball, initially, you're totally useless until your cerebellum kicks in and corrects for the fact that when you thought you'd thrown it in one direction, your eyes tell you you're throwing it in a different direction.  After a little while, you can throw and catch because the cerebellum has done its job.

Meera -   I actually remember having a go on that around the office and it did adapt really quickly.  I was really surprised.

Ben -   It's strange and frustrating when you take the glasses off again and you find that you can't throw and catch for a little while.

Meera -   Yeah, but I'm not amazing at that any way, so it's alright.

Ben -   Hopefully, Dave will be back in action for another Kitchen Science next week.

We'd like to say huge thank you to Dr. Ellie Dommet at the Open University and Professor Patrick Haggard at UCL for helping out with this week's experiment.


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