Arms crossed, Noémie, 39, boldly advances. The young woman places her heel against the toe of the opposite foot and walks step by step along a line drawn on the ground. Researchers note the number of steps she takes without faltering. Then she Noémie repeats the exercise with her eyes closed, a pure challenge. She often staggers, the two experimenters who supervise her are alert.
This test is a classic for assessing balance disorders. Noémie underwent it on the premises of the University of Caen, at the beginning of October, where about thirty volunteer patients from all over France were gathered. Over four days, a battery of tests allowed the researchers to assess their postural balance, their ability to walk in the presence of obstacles, their perception of angles, distances and time, and their ability to solve various cognitive tasks. Their bone density was measured, their brains underwent magnetic resonance imaging (MRI). Everyone is suffers, like Noémie, from a deficit of the vestibular system.
The vestibular system? An unknown sixth sense. Yet it plays a crucial role in maintaining our balance, the stability of our gaze, our orientation in space. Feeling the acceleration or deceleration of an elevator, experiencing a sharp turn in a car are all sensations we owe him. He still intervenes – but, here, his way of acting is more obscure – in our perception of time, in the rhythm of our hormonal secretions, in the quality of our sleep, in our bone density…
However, “we realize its existence only in certain ‘pathological’ situations, such as seasickness, alcohol poisoning, vertigo”, underlined, in 2006, two researchers from the Collège de France, Werner Graf and François Klam. Is it because this little jewel of precision, a perfect illustration of nature’s engineering capabilities, is kept in the labyrinth of our two ears, hidden from view?
A variety of sensors
Guardian of our balance, the vestibular system does not act alone. It has two precious allies: the visual system and proprioception. A seventh sense, for its part, which mobilizes a panoply of sensors sensitive to stretch and pressure, scattered over our muscles, tendons and ligaments. These buried sentinels transmit location data from different parts of our bodies to the brain. Eventually, our brains will integrate messages from these three systems: vestibule, visual system, and proprioception. And it will convert them, after an intelligent calculation, into coherent information. For instance, “ the body is erect, the head is turned to the right”.
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