To be tickled, it turns out, requires the element of surprise.
Scientists used an fMRI to examine neural responses when subjects experienced a tactile stimulus that was either self-produced or externally produced. In other words, the subjects tickled themselves or were tickled by others.
“More activity was found in somatosensory cortex when the stimulus was externally produced. In the cerebellum, less activity was associated with a movement that generated a tactile stimulus than with a movement that did not.”
When you try to tickle yourself, your cerebellum (the part of the brain that regulates fear and pleasure responses) predicts your movements and provides a signal that cancels the sensory response to self-generated stimulation.
It is not known whether the words “coochie-coochie-coo” were uttered during administration of the externally produced tactile stimulus.
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