Sunday, 23 October 2016

Rubber Hands and Mirror Boxes: Illusions of the brain

For anyone that regularly reads my blog, you will know that I studied Neuroscience for my undergraduate degree university and love learning about the brain! Although I study a different course now for my masters, I still love spotting news stories that pop up about the brain every now and then.

One of the more recent news stories I have read discussed the 'rubber hand illusion', which was used by a team of researchers in Italy to demonstrate how our brains can understand our bodies. This illusion explores the idea of shifting our perception of ourselves, tricking us into thinking that a fake body part is our own. The experiment worked by asking volunteers to sit with both arms on a table, but with their right hand covered by a box. A lifelike rubber hand was placed in front of them and aligned with the right side of their body where the hand would have been.

Source: The Guardian/China Photos/Getty Images
Next, the researchers stroked the middle finger of the hidden right hand at the exact same time as they did to the fake hand. After a couple minutes, the volunteers began to believe that the fake hand belonged to them. This illusion works by sending conflicting visual and sensory (touch) information to the brain, which then sees no other conclusion but that the fake hand is part of the volunteer's body.

This figure demonstrates the science behind the illusion
Source: Figure 1A, della Gatta F. et al.'Decreased motor cortex excitability mirrors own hand disembodiment during the rubber hand illusion', 2016, eLife
Interestingly, when the researchers carried out different techniques to work out exactly what was going on inside the brain during the illusion, they found that electrical impulses to the volunteer's right hands decreased dramatically. This showed that the brain was shutting down impulses to the right hand, as if preparing to stop using it because it not longer believed it to be part of the body. this demonstrates just how strong the illusion is!

The researchers believe their work may be able to help others who suffer from body ownership disorders that may have occurred after stroke or other brain damage. If you'd like to read the study in full, please click here.

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Reading about this study reminded me of one of the first Neuroscience books I read, called 'Phantom Limbs', by the brilliant Vilayanur S. Ramachandran. The book described different ways our brains can react to limb damage or loss, as well as explaining methods that can be used to help cope with the loss. For example, Ramachandran was working with a patient named Jimmy, who had lost one of his hands. However, Jimmy felt like his missing (phantom) hand was constantly (and painfully) clenched shut.

In an attempt to help relieve Jimmy of this pain, Ramachandran put a mirror between Jimmy's arms and asked him to slowly move his healthy and phantom limbs together. Jimmy looked at the mirror whilst doing this, so effectively was looking at the mirror image of his healthy hand in the place where his phantom would have been. After doing this for a period of time, Jimmy's brain was tricked into thinking that his phantom limb was moving in a normal way. He was soon able to release his painful clenched wrist. This is an example of sensory conflict - Jimmy's visual system would have been telling him that the phantom limb is real and moving, but his brain would be denying existence of the hand. Ramachandran called this 'Mirror Visual Feedback' therapy.

A demonstration of the mirror illusion, convincing the volunteer of two intact healthy arms
Source: BBC News
I have also covered another similar phenomenon in a previous blog post. In this, I discussed the case of Ian Waterman, who lost his sense of his own body and its position relative to space around him. This sense is called proprioception. If you'd like to read my previous blog post on this, please click here!

What do you think of these illusions? Do you think they would work on you?! Let me know in the comments!

4 comments:

  1. I have not read too much on this topic and have to say I found this to be very interesting! Thank you for sharing. xxx

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  2. This is all new to me but really thought provoking. Amazing how the human body works.

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  3. Wow! How amazing is that?!!? The human body is absolutely fascinating, i love reading how it all works!!! Xx

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  4. A very interesting post, Emily. I wonder if this could cure allergies as well in another stage of this illusion, if you could trick your brain to believing that broccoli is actually carrots, for example. Also, what if you could cure cancer by doing this? You could take this illusion to another stage, and do what cancer does to you in a way. Since cancer makes you destroy your t-cells and make you think that a lot of necessary things are trying to kill you, and that you need to get rid of them, you could change the target. You could try to make a stage of the illusion that is not visual, and then you could convince your brain that the cancer is actually the things that the cancer is trying to make you destroy. This is a great post, and something that I will be thinking about for a while.

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