The ability to distinguish between self and others is extremely important. A new-born child develops an understanding of where their own body ends mainly through being touched by those who care for them. Problems with the self-concept, such as the ability to recognize one's own actions, are common in several psychiatric disorders. Most people cannot tickle themselves, but some patients with schizophrenia can, suggesting that their brain interprets sensory perceptions from their own body differently.
Most people have a ticklish spot somewhere on their bodies, and laughing when another person tickles you is a natural reaction. Scientists have discovered that the feeling experienced when we are tickled causes us to panic and is a natural defense to the likes of spiders and bugs. Slight tickles from insects can send a chill through your body letting you know something is crawling on you.
That same ticklish feeling sends us into a state of panic and elicits a response of uncontrollable laughter if a person tickles us. Even if you know that you are about to be tickled, the fear and unease of someone touching and possibly hurting you causes you to laugh. Some people are so ticklish that they begin laughing even before they are touched.
So, if someone else's touch can tickle us, why can't we tickle ourselves? Much of the explanation is unknown, but research has shown that the brain is trained to know what to feel when a person moves or performs any function. We aren't aware of a lot of the sensations generated by our movements. So, if we grab our sides in an attempt to tickle ourselves, our brain anticipates this contact from the hands and prepares itself for it. By taking away the feeling of unease and panic, the body no longer responds the same as it would if someone else were to tickle us.
Brain scientists at the University College London have pinpointed the cerebellum as the part of the brain that prevents us from self-tickling. The cerebellum is the region located at the base of the brain that monitors our movements and it can distinguish expected sensations from unexpected sensations. An expected sensation would be the amount of pressure your fingers apply to your keyboard while typing.
An unexpected sensation would be someone sneaking up behind you and tapping you on the shoulder. While the brain discards the sensation of typing, it pays a lot of attention to someone tapping on your shoulder. The difference in reactions from expected to unexpected is a built-in response.
In the experiments scientists examined what happens in various parts of the nervous system when a person is touched by another person compared to touching themselves and found that the brain reduces the processing of the sensory perception when it comes from self-touch.
The skin contains sensory receptors that react to touch, pressure, heat and cold. Information about touch is transmitted to the spinal cord and on to the brain where the perception is processed in several steps in different regions of the brain.
In the experiments volunteers laid in a magnet resonance camera which recorded images of brain activity and were requested to stroke their arm slowly with their own hand, or were told that a researcher would stroke their arm.
What they discovered was a very clear difference between being touched by someone else and self-touch. When a person touched themselves activity in several parts of the brain were reduced. The differences actually began to be noticed in the spinal cord even before the perceptions reached the brain.
The results are compatible with a theory that suggests the brain attempts to predict the sensory consequences of everything we do. Consequently, the brain does not attach as much importance to sensory perceptions caused by our own bodies because it's expecting to receive such information.
Apparently when someone else touches us we can never be exactly sure what they're up to, so the brain is on high alert.