Vestibular reafference shapes voluntary movement

The vestibular organs in the inner ear are commonly thought of as sensors that serve balance, gaze control, and higher spatial functions such as navigation. Here, we investigate their role in the online control of voluntary movements. The central nervous system uses sensory feedback information during movement to detect and correct errors as they develop. Vestibular organs signal three-dimensional head rotations and translations and so could provide error information for body movements that transport the head in space. To test this, we electrically stimulated human vestibular nerves during a goal-directed voluntary tilt of the trunk. The stimulating current waveform was made identical to the angular velocity profile of the head in the roll plane. With this, we could proportionally increase or decrease the rate of vestibular nerve firing, as if the head were rotating faster or slower than it actually was. In comparison to movements performed without stimulation, subjects tilted their trunk faster and further or slower and less far, depending upon the polarity of the stimulus. The response was negligible when identical stimulus waveforms were replayed to stationary subjects. We conclude that the brain uses vestibular information for online error correction of planned body-movement trajectories.