Why can’t we tickle ourselves while schizophrenics can?

Have you ever tried to tickle yourself? Try it; you will find that the feeling will be nothing like the sensation you get when someone else tickles you. But why is this the case?

tickle 300x238 Why can’t we tickle ourselves while schizophrenics can?The simplest answer to this question is to assume that when you tickle yourself you’re expecting the sensation, so are less likely to react. However, functional magnetic resonance imaging (fMRI) has shown that activity in an area of the brain known as the somatosensory cortex is comparable both when subjects are tickled unexpectedly and when they are warned that they are about to be tickled. This provides evidence that the brain responds to an expected sensation in the same way as it does to an unexpected sensation. Meaning that expectation alone cannot be the explanation for our inability to tickle ourselves.

The brain is constantly receiving sensory input  (information about our experiences communicated by our physical senses)  from everything we touch, see, hear, taste and smell. This constant barrage of information must be sorted and processed by the sensory systems of the brain in order for us to make sense of the world around us. Arguably, the most important feature of normal brain processing is the ability to identify and extract information about externally-induced changes in our environment. Therefore, in order to differentiate between spontaneous environmental changes and those we cause ourselves, the brain categorizes self-produced movements as being less significant than those initiated external to our bodies. Indeed, fMRI scans have identified increased activity in the somatosensory cortex in response to externally produced tickling (as used in the above study) compared to little or no change in activity seen when participants tickle themselves. This data suggests that activity in the brain differs in response to externally and internally produced stimuli, reinforcing the neurological basis for our ability to consciously distinguish between the two.

Cerebellum NIH 300x218 Why can’t we tickle ourselves while schizophrenics can?

Cerebellum in purple

Research suggests that this ability to recognise a self-initiated movement may depend on a structure at the back of the brain known as the cerebellum. Circuits within the cerebellum have been termed the bodies ‘central monitor’ and may be the key to distinguishing between self-produced sensations and external stimuli. Neurons of the cerebellum have the capacity to calculate strong and accurate predictions about the sensory consequence of self-tickling. This system takes predictions about our movements and compares them with actual sensory feedback produced by the action. The difference between the two is known as an ‘error signal’. If you attempt to tickle yourself, your internal ‘central monitor’ will accurately predict the sensory consequence because the movement is self-produced and there will be little or no difference in error signal. In contrast, when someone else tickles you (even if you are aware it is going to happen), you will not be able to predict exactly what the sensory stimulation will feel like; that is, its position or strength. Therefore, there will be a difference between your brains prediction and the actual sensory feedback.

So it seems that you can’t tickle yourself? Well, at least this is usually the case. However, research has now stumbled upon a remarkable feature of schizophrenia showing that, unlike the rest of us, schizophrenics actually have the capacity to tickle themselves! It has been suggested that this phenomenon may be a caused by neurological changes in the schizophrenic brain which disable the patient’s ability to detect self-initiated actions. It is possible that biochemical or structural changes in the brain cause a malfunction in the predictive system of the cerebellum. This results in a miscommunication of information concerning internally- vs. externally-generated actions. Essentially this means that, although the patient is able to process the intent to move and is aware the movement has occurred, they cannot then link the resulting sensation (the tickle) with their internal knowledge of making the movement. It is therefore possible that this deficit in self-awareness or monitoring could result in thoughts or actions becoming isolated from the internal appreciation that they are producing them. Consequently, schizophrenic patients may misinterpret internally-generated thoughts and movements as external changes in the environment.

Our ability to control the magnitude of our responses based on prior knowledge of our own actions appears to have numerous advantages. This includes the ability to distinguish between real external threats, such as a poisonous spider crawling up our leg, and those we create ourselves, for example resting our own hand on our leg. Indeed, recognising the difference between an external threat and a self-induced false alarm may, in some situations, be the difference between life and death. The multifactorial basis of the tickling sensation indicates a staggering complexity in central processing in the brain. Science is currently unravelling these complexities and, with luck, this research may lead to both a better understanding of disorders such as schizophrenia and may point the way towards novel treatment strategies.

Post by: Isabelle Abbey-Vital

button print gry20 Why can’t we tickle ourselves while schizophrenics can?

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10 Responses to Why can’t we tickle ourselves while schizophrenics can?

  1. Pingback: Some People Can Tickle Themselves | Smart News

  2. Cactus says:

    So, if I happen know someone who is so unfortunate he can tickle himself, he is by necessity from what I can read here an undiagnosed schizophrenic, if he is not already unknown to me diagnosed?! I really do not believe it! Some more facts on this claim, please.

  3. thebrainbank says:

    Thanks for your comment. Research has identified that schizophrenics have a altered perception of self touch/tickling, in which they cannot distinguish between self tickle and external tickle. The fact that someone can tickle themselves does not mean they are schizophrenic, but many of the changes in the brain associated with schizophrenia can drive these symptoms in patients. If you’d like to read more here is a good link http://www.ncbi.nlm.nih.gov/pubmed/?term=The+perception+of+self-produced+sensory+stimuli+in+patients+with+auditory+hallucinations+and+passivity+experiences%3A+Evidence+for+a+breakdown+in+self-monitoring

  4. Jo says:

    Interesting. I wonder if this would apply across body hemispheres to a patient who has had their corpus collosum severed. It would certainly be an irritation if the uncontrolled hemisphere of the brain was a tickle-phile!

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  7. Bim says:

    This makes me a little worried… I had schizophrenic experiences in 10th grade. They suddenly stopped occuring and my therapist said that some people experience such events when they are under stress etc. and it was nothing serious after all.
    I can tickle myself, so much that it can become unbearable…
    I will not ask for advice on the internet… Should I have a talk with a therapist again O.o?

    • thebrainbank says:

      This post is based on a research paper which can be downloaded here: http://tinyurl.com/lh4w63l . Although the observed effect is certainly interesting I don’t think that its findings can be used to replace a psychiatrist’s diagnosis.

      If you look at the sample size for this study it’s relatively small, also the study only investigates a small number of individual groups (schizophrenics – with or without psychosis – (23 people), ‘normal – whatever that is -‘ individuals (15 people) and people suffering from affective disorder (18 people)), this certainly doesn’t represent the whole population, thus doesn’t rule out other factors which may lead to someone to be able to tickle themselves.

      So although I think the research is certainly interesting, it is probably only part of a much bigger picture – like many scientific studies.

      I would suggest that if you have not experienced any traditional symptoms there is no need to worry. But, ultimately you need to do whatever makes you feel most comfortable. I am not a medical doctor, so can not really offer advice on this issue.

      Many thanks for commenting, I hope you find reading the actual study helpful.

      Sarah

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  9. brandi says:

    Oh shit !!! I can tickle myself ! Should i go see a doctor ?!

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