To perform movements correctly and stay balanced, humans must constantly assess how their bodies move relative to the environment. For example, if we lean against a wall or the floor slopes, our brain unconsciously adjusts our movements. New research from Erasmus MC now shows that these corrections are more complex than previously believed.
The neuroscientists, led by associate professor Patrick Forbes, had a group of volunteers stand on a custom-made robotic balance simulator (see photo). The participant stands on a plate with sensors. A computer uses information from these sensors to control the installation and records all the movements and forces of the test subject. Effectively, the participant controls their own movement in synchrony with the robot, as if they were standing naturally.
PhD student Matto Leeuwis demonstrates the robotic balance simulator.
Using the robot, the scientists can simulate balance situations and measure how participants respond. In this case, the participants first learned a Pavlovian response: after hearing a sound, their balance was disrupted by the robot. In response, they corrected their posture to avoid falling. When the scientists changed the robot’s settings, they noticed something strange. Without telling the participants, the robot took over their balance control. Even in this situation, where participants had no control over their movements, the learned balance correction after hearing the sound persisted.
Multiple representations
This is remarkable because previous research shows that the brain does unconsciously suppress signals from the vestibular system when control over movements is removed. Apparently, this is different for conditioned balance corrections, as shown by the robot experiment. The response persists, even if it is ineffective because the robot has taken over control. PhD student Matto Leeuwis explains: ‘The prevailing theory was that the brain combines incoming signals to build a single image of ourselves and the world. Our results suggest that the brain may not rely on one understanding of our body and the world around us. Instead, multiple representations of ourselves may exist in our brain to guide different behaviors.’
This is important information for neuroscientists because it teaches them something fundamental about how the balance system in the brain works. Future studies could explore how these representations are formed in the brain and how they are affected by brain disorders such as cerebellar ataxia, a condition where a part of the brain called the cerebellum doesn’t work properly, making it hard for a person to control their movements and balance.
