Scientists have been asking questions about the somatosensory consequences of our own movements for decades. By now, we know that the brain (probably the cerebellum) anticipates and cancels out incoming information about self-produced movements, creating what is known as an ‘efferent copy’. Because every time we make a movement, the brain attenuates the sensations coming from our body, including those coming from the skin: if we try to tickle ourselves we are forced to move, and therefore we cannot stimulate ourselves enough. But why can’t we tickle ourselves?

Why don’t we laugh when trying to tickle ourselves?

To find the answer, they studied brains of 16 people with a scanner. Furthermore, they tried to tickle themselves on the palms of their hands and feet. And, later, they repeated the experiment by having other subjects tickle them.

They examined whether involuntary movements induced by self-stimulation and, on the other hand, stimulation induced by a third party.

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The foot stimulus alone was scored as tickling as when the experimenter tickled the participant’s foot, using an identical stimulus as the self stimulus. Therefore concluded that magnetic stimulation of the motor cortex is unlikely to generate an efferent copy of the motor system’s output, as self stimulation does.

Thus, they verified that the areas that respond to touch and pleasure were much less activated when they were done by oneself. Furthermore, they concluded that self-generated tactile stimulation is attenuated because internally the sensory system predicts the sensations that our movements will produce in us at the same moment that the motor system gives the order to execute them.

The efferent copy

The concept of ‘efferent copy’ is basic in neurophysiology. Because it refers to how the individual evaluates reality, internally and externally, and how the individual interacts with himself. It alludes to the concept of anticipation of movements.

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To understand it, our partner organizes a surprise party for us, and we find out about it through a friend or family member. When the party arrives, the surprise and emotional effect diminishes. Why? Because we already knew what was going to happen. In this case, something similar happens: if there is no surprise, there is no tickling either.

The self-realized stimuli to ourselves travel along a double path. The brain, on the one hand, is giving the order to carry out said movement. On the other, he is receiving the expected stimulus, the result of that movement. In these cases, the muscles carry with them an order, which is sent to the sensory receptors. There is no surprise.

According to the neurologist and musician Arturo Goicochea, the efferent copy refers to the absence of self-awareness; allows automatic movements , which are classified as harmless, and are tolerated and filtered as such. In addition, as the neurologist explains in his blog, given that the efferent copy allows us to predict movements and stimuli. It also allows us to evaluate “the costs and benefits of each movement, depending on each objective and each context.”