On Earth, human beings can feel and “see” the effects of gravity on their bodies and surroundings. The human brain naturally takes gravity into account in several cerebral processes used for orientation, visual perception and motor control. In microgravity, however, many ‘normal’ references are lacking: objects float in space and the notions of ‘up’ and ‘down’ are no longer relevant. As a result, the brain receives unfamiliar information. Could this mean that the disorders experienced by astronauts are due to certain processes being altered by changes in the gravitational field? How does the brain adapt?

This issue has been investigated for the last fifteen years by means of experiments performed during the Cognilab and Neurolab missions. In conjunction with a number of French research laboratories, CNES has developed a neurosensory stimulation platform, SENS*, based on virtual reality. This unit can be used for neuroscience experiments involving astronauts before, during and after flights on the ISS. It includes stimulators which act on subjects and sensors which record their reactions. Using virtual reality, the subject is immersed in the same situation both on Earth and in Space, thus ensuring that the results are consistent.

Three experiments are currently being developed.

• Affordance tests the way subjects perceive distances and dimensions, which usually depends on the height of the observer’s eyes relative to what he is looking at. However, in the ISS, this is no longer meaningful as the astronaut is never planted firmly on the ground. Wearing a virtual reality headset with stereoscopic vision, the subject is asked to estimate the overall dimensions of a virtual room and to determine his size in relation to it.
• The Voila set of experiments investigates spatial references which are fundamental to our orientation and perceptions. One of the experiments involves placing the subject in a virtual corridor in which he has to determine whether he or the corridor is moving.
• 3D Space is designed to test the hypothesis that altered visual perception affects motor control. To do this the subject is asked to reproduce shapes or text on an electronic pen pad.

Better understanding of how the brain works and interacts with the nervous system will help further medical research, particularly into neurological disorders.

The Cadmos microgravity research centre will be responsible for SENS once it becomes operational. Cadmos will implement the experimental protocols designed by researchers from the various associated laboratories, and monitor in-flight operations.

 _{* Système d’Expérimentation NeuroSensoriel}

_{Last updated : March 2007}