The vestibular organ sits in the inner ear and controls balance and gaze control. Now, Brian Day and Raymond Reynolds of University College London report in the August 9 issue of Current Biology that it also serves as an online control center for voluntary movements.
The team had volunteers sit on a stool while blindfolded and asked them to tilt their upper bodies 10 degrees to the right. After each volunteer learned the movement through repeated trials, the team stimulated their vestibular organ via electrodes placed on the bone just below and to the rear of the ear, called the mastoid process. The added electrical stimulation caused the volunteers to accelerate or slow their rate of tilting in a predictable manner. The same stimulus had no impact when the volunteers were sitting still.
These results demonstrate that the vestibular organ senses movement and adjusts the rate or direction when the movement does not match an expected motion. Like a computer, the vestibular system makes those changes while the motion is continuing.
“Vestibular feedback is used during voluntary movements,” says Reynolds, and not just for controlling posture or balance.