Bang goes the bus top and still no tickle

Last night, I walked past a bus stop adorned with a poster advertising the new BBC science programme Bang Goes the Theory asking “Is it possible to tickle yourself?” and giving a number to text for an explanation.

Fantastic, I thought. Neuroscientist Sarah-Jayne Blakemore’s work on the role of action prediction in the sensory attenuation of self-produced actions summarised in 160 characters.

But here’s the response I got sent to my phone:

Your brain tells your body not to react when you tickle yourself hard, but skin with no hair is sensitive to a light touch. More at http://bbc.co.uk/bang

Admittedly, I was a little worse for wear last night, but even in the cold hard light of day, this doesn’t make a lot of sense.

The second bit (“skin with no hair is sensitive to a light touch”) just seems irrelevant to the question, the webpage has nothing more and the actual explanation is kinda screwy.

Your brain is not telling your body not to react because, except for reflex actions (which are handled by reflex arcs and can be managed entirely by the spinal cord), sensory reactions are handled by the brain.

So if you’re taking this line, a more accurate description is that your brain is telling your brain not to react but this still explains virtually nothing about why you can’t tickle yourself.

However, a scientific paper [pdf] entitled ‘Why can’t you tickle yourself?’ addresses exactly this question.

The science of this is quite well known (in fact, it was featured in the original Mind Hacks book as Hack #65) but in summary it seems that the brain simulates of the outcomes of actions based on your intentions to move because the actual sensory information from the body takes so long to arrive that we’d be dangerously slow if we relied only on this.

This slower information is used for periodic updates to keep everything grounded in reality, but it looks like most of our action is run off the simulation.

We can also use the simulation to distinguish between movements we cause ourselves and movements caused by other things, on the basis that if we are causing the movement, the prediction is going to be much more accurate.

If the prediction is accurate, the brain reduces the intensity of the sensations arising from the movement – for good safety reasons, perhaps – we want to be more aware of contact from other things than touches from ourselves.

So Aunty BBC, here’s one you can use for free:

Your brain predicts the effects of movement and reduces sensations if it guesses right. We guess our own actions better, so it tickles less. http://is.gd/2978A

The next one will cost you the 10p I spent texting Bang Goes the Theory for an inaccurate explanation.

pdf of scientific paper ‘Why can’t you tickle yourself?’
Link to Hack #65 in Mind Hacks.

One Comment

  1. Posted August 9, 2009 at 5:47 pm | Permalink

    That’s a beautiful explanation.


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