During counterclockwise (left) rotation of the head, the horizontal semicircular canal and its attached cupula also rotate to the left. Initially, the cupula moves more quickly than the endolymph fluid. Thus, the cupula is dragged through the endolymph, as a result, the cilia on the hair cells bend.
If the stereocilia are bent toward the kinocilium, the hair cell depolarizes (excitation). If the stereocilia are bent away from the kinocilium, the hair cell hyperpolarizes (inhibition). Therefore, during the initial counterclockwise (left) rotation, the left horizontal canal is excited and the right horizontal canal is inhibited.
After several seconds, the endolymph "catches up" with the movement of the head and the cupula. The cilia return to their upright position and are no longer depolarized or hyperpolarized.
When the head suddenly stops moving, the endolymph continues to move counterclockwise (left) dragging the cilia to the opposite direction. Therefore, if the hair cell was depolarized with the initial rotation, it now will hyperpolarize. If it was hyperpolarized with the initial rotation, it now will depolarize. Therefore, when the head stops moving the left horizontal canal will be inhibited and the right horizontal canal will be excited.