Swiss study looks at why no two bodily movements are the same

We can tend towards stereotypical actions, but our nerve reactions tend to stay unique. Keystone-SDA

Each time we reach for a coffee cup, the movement is different. According to the University of Fribourg, this variability is down to nerve cells, which the brain uses to correct every movement.

The nerve cells act as the brain’s “optimal estimators” in that they combine real sensations with their own predictions, the University of Freiburg said on Wednesday. Fluctuations in movements are caused by proprioception, or the “sixth sense”, which provides information about the position of our body in space without us having to look.

Every movement is based on feedback from sensors in the muscles, tendons and joints, the statement continued. The proprioceptors then tell the brain about where the body is and how it is moving, according to the findings, which were published in the scientific journal Current Biology.

Researchers studied mice that had been trained to reach for drops of water. To do this, they recorded the movements using high-speed cameras. Using two-photon microscopy, they identified individual proprioceptive neurons and were able to eliminate them at their cell bodies using a narrowly focused laser beam. The approach differs fundamentally from traditional methods, which involve disabling an entire region of the brain.

Afterwards, the mice were just as capable of reaching for the drops, but their movement patterns changed. “The sequences were more disordered and, at the same time, increasingly stereotypical in form – as if the movements were becoming more robotic,” lead author Mélanie Palacio-Manzano said in the press release.

According to the study, this shows that the brain relies less on sensory information from the body than on what it has already anticipated. When the nerve cells are inactive, the movements remain precise, but their sequence becomes increasingly stereotypical.

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Translated from German, reviewed by an English Department journalist.