Imagine a world where every step you took, every turn you did, and every move you made forced you to giggle. That world does not exist because it is nearly impossible to tickle ourselves. Have you ever wondered why you laugh when someone tickles your stomach, but get no response from yourself when you try to tickle your own stomach? The answer is quite simple, and it is all thanks to science.
http://vidyasury.com/wp-content/uploads/blogger/-pl7Th-dqobA/T5BZHB-XNPI/AAAAAAAAF4w/3rpE7epXVLA/s1600/Vidya%2BSury%2BTickle.gif
The human brain has the ability to distinguish between our own touch and the touch we feel from others. Guy Claxton of the University of London Institute of Education uses the predictability of the stimulus to explain this. When someone else tickles you, your brain is uncertain about the “place and time of onset of the stimulus.” However, when you try to tickle yourself, the brain knows exactly where it is coming from and when it is coming. 49 students, with ages ranging from 25 to 45 yrs, were used in Claxton’s study. The tickling stimulus was applied to a bar forearm comprised of five strokes with a feather for five seconds. Since this study was conducted in 1975, the method used to create the four main conditions aren’t as technical. The four conditions are as follows:
- Subjects shut their eyes and allowed themselves to be tickled by someone else. This created unpredictable stimulus.
- Subjects kept their eyes open and allowed themselves to be tickled by someone else. This created relatively predictable stimulus.
- Subjects, with open eyes, held a feather (tickling stimulus) in their hands. However, someone else moved theirs hands to crete and involuntary movement.
- Subjects tickled themselves.
The results showed that unpredictable and involuntary touching produced a greater sense of ticklishness. The p-value of this experiment has been recorded and less than .001. That proves that this study is highly reliable. I believe these results because the study was done ethically and the p-value is significant. Since this was an experimental study, reverse causation can be ruled out. While chance could still be a factor, it seem highly unlikely because of the p-value.
More recently, Sarah-Jayne Blakemore of University College London investigated how the brain differentiates between the touch of the self and the touch of others. The study, consisting of six normal right-handed individuals (four females and two males with a mean age of 33 years) was approved by the National Hospital for Neurology and Neurosurgery. The participants gave consent to be a part of the study, so they knew exactly what was being tested on them. Split into two 12-minute sessions, the subjects “underwent 200 fMRI scans.” The subjects laid chest up on an MRI bed. A rod with a piece of soft foam at the end was placed in the hand of each subject. They then randomly underwent four different conditions:
- Condition A: “Self-produced tactile stimuli (touch)”
- In this condition, the subjects made “vertical sinusoidal movements of the rod with the right hand.” Tactile stimulation was produced in their left hands. Subjects we told that stimulation in the left palm would occur.
- Condition B: “Self-produced movement; no tactile stimuli (move)”
- Similar to Condition A, in Condition B, subjects made “vertical sinusoidal movements of the rode with the right hand.” However, tactile stimulation in the left hand was removed. Instead, subjects were told that in this condition, tactile stimulation would not occur.
- Condition C: “Externally produced tactile stimuli (feel)”
- Subjects did not move. Instead of producing stimulation themselves, the experimenters “moved the tactile stimulus sinusoidally across the subjects left palm.”
- Condition D: “Rest”
- Just like how it sounds, subjects were told to stay still and to not move.
http://www.nature.com/neuro/journal/v1/n7/pdf/nn1198_635.pdf
To the right are the results of the study in graph form. As you can see, only the conditions with no self-generated movement produced a BOLD signal. A BOLD signal measured the blood-oxygen-level dependent. In this case, it measures the sensations that are brain feels. More sensations were created in Conditions C and D than in Conditions A and B. Blakemore’s team did a fine job of conducting this experiment. The p-value has been recorded as less than 0.05 which is significant. This shows that the results are reliable. Personally, I believe these results. The structure of the study was nice. However, the sample size is very small. Six people is not enough to draw clear conclusions from. I would like to see this study model conducted on a larger sample size to see if the same conclusions are reached. I don’t think that the results will differ, however it is important to test on a large group of people because it accounts for differentiation.
http://www.todayifoundout.com/wp-content/uploads/2010/08/tickling.jpg
So, the answer really is quite simple. Tickling is due to predictability. When we know the time and place of the stimulus, we won’t feel a tickling sensation. But if the stimulus is a mystery, our neurons send a message to the brain that makes us feel a tickling sensation. So go ahead and try to tickle your stomach. I am 99% sure that you won’t start laughing. But have your friend tickle you, and you will be begging him or her to stop!
I thought this was a very interesting post because I have realized that you indeed cannot tickle yourself. Your beginning statement was a good attention getter, approaching the idea of if everyone constantly did giggle, and what the world would be like. It was interesting to see how science can relate to such a thing as tickling through touch. On the BBC website, an article you used in your blog, also states, “’It’s interesting that people with schizophrenia can tickle themselves and we think that’s associated with things like delusional and alien control of limbs.’” This could be another way to extend the blog, finding a way to intertwine how others with mental disabilities, like schizophrenia, could influence and altar this idea. In the end though, I’m glad I know understand that it’s all due to predictability!