Why you can't tickle yourself: what your brain knows that your skin does not
Sensory attenuation: how your brain turns down your own touch
Every time you move, your brain quietly forecasts what you will feel, then turns that feeling down. Why would it hide your own touch from you?
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When your brain tells your fingers to move, it does not only send the order. It also keeps a copy of it, the way you keep a copy of a letter you send.
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Scientists think that a part at the back of your brain, the cerebellum, reads the copy and makes a forecast: a touch is coming, right here, right now, this strong.
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Then the real touch comes in from your skin. It matches the forecast, so your brain turns it down. Scientists call this sensory attenuation. So a tickle that your brain saw coming is only a touch.
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Scientists watched this in a brain scanner. When people made the touch themselves, the touch area of the brain worked less than for the same touch from outside.
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Why would a brain do this? You move all day, your clothes rub and your hands touch each other. Scientists think that with your own touches turned down, a touch from outside stands out. So when the conductor taps your shoulder in the dark, you jump.
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Go further
The real name of the copy, and your voice.