The fact that you cannot tickle yourself is due to the phenomenon of tactile suppression: the brain predicts the effect of the self-generated touch and weakens the tactile sensation accordingly.
This mechanism is often disrupted in schizophrenic patients, which is why they have problems distinguishing self-generated movements from those generated by others.
Scientists from the University of Gießen have now shown that tactile suppression is very specific to the respective sensory stimulus.
Sasha Zoske
Sheet maker in the Rhein-Main-Zeitung.
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The researchers asked 32 subjects to run a finger over surfaces of varying roughness.
The materials were chosen to stimulate different types of receptors in the skin.
Even before the surface was touched, a reduced sensitivity of precisely those receptors that would be activated by the material in question was evident.
The brain therefore makes an exact prediction about the stimulus to be expected and adjusts the sensitivity of the skin accordingly.