Neurological control of horizontal and vertical components of oblique saccadic eye movements

Abstract

The horizontal and vertical components of oblique saccadic eye movements are not always tightly crosslinked; often they are completely independent. Most of the time the two components do not start and end simultaneously. The neurological bursting and pausing of the extraocular motoneurons that underlie the generation of these oblique movements will, correspondingly, not be synchronized. Evidence for some crosstalk between the horizontal and vertical systems comes from observations that pure horizontal or pure vertical saccades are rarely straight but are almost always curved. The hooks seen frequently in oblique trajectories are caused by dynamic overshoot in one or both components. Vertical saccades are slower than horizontal saccades, with downward saccades being the slowest. Oblique saccades, being the result of the summation of forces of the horizontal and vertical systems, can be faster than either purely horizontal or vertical saccades of the same amplitude.