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. 2019 Nov 14;4(22):e128397. doi: 10.1172/jci.insight.128397

Figure 1. Coplanar pairs of semicircular canals in the vestibular labyrinths encode 3D head rotational velocity in 3 mutually orthogonal components.

Figure 1

Relative levels of activity within vestibular nerve branches innervating a labyrinth’s 3 semicircular canals encode 3 mutually orthogonal canal-aligned components of the head rotational velocity’s 3D axis. The vestibulo-ocular reflex (VOR) drives eye rotations that counteract head rotation to keep images stable on the retinae. (A) Pairs of coplanar canals normally encode 3 linearly independent components of head rotational velocity about axes perpendicular to the left horizontal (LH) and right horizontal canals (LHRH or +z axis), left anterior and right posterior canals (LARP), and right anterior and left posterior canals (RALP). By convention, positive rotations denote right-hand rule rotations as shown by black arrows. Each canal is most sensitive to rotation about an axis approximately perpendicular to its anatomic plane. (B–D) Head rotations about canal axes that excite the LA, LH, and LP canal, respectively, normally drive VOR responses that rotate both eyes in the opposite direction about the LARP, LHRH, and RALP axes. Physiologically excitatory directions (shown by gold arrows) are not always positive by the right-hand rule mathematical convention. (E) Head rotation about an arbitrary axis excites or inhibits each canal according to a cosine dependence on the angle between the axis of head rotation and the canal’s anatomic axis. (F) Relative activity on the 3 canals in each labyrinth (and their coplanar partners in the other ear) normally drives a VOR response that helps keep images of Earth-stationary objects stable on the retinae. Without the VOR, image slip on the retinae degrades vision during quick head rotations. Although most studies of the VOR measure and describe only yaw (z/LHRH in panel A, also called “horizontal”) and/or pitch (y/PITCH, also called “vertical”) components, all 3 components of the 3D VOR are required to maintain stable vision, and measurement of all 3 components is required to accurately estimate the relative levels of activity on each of a labyrinth’s 3 semicircular canals. Reproduced by permission from Labyrinth Devices, LLC, ©2019.