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Behavioral/Systems/Cognitive Three-Dimensional Kinematics at the Level of the
 

Summary: Behavioral/Systems/Cognitive
Three-Dimensional Kinematics at the Level of the
Oculomotor Plant
Eliana M. Klier, Hui Meng, and Dora E. Angelaki
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110
Motorsystemsoftenrequirethatsuperfluousdegreesoffreedombeconstrained.Fortheoculomotorsystem,aredundancyinthedegrees
of freedom occurs during visually guided eye movements and is solved by implementing Listing's law and the half-angle rule, kinematic
constraints that limit the range of eye positions and angular velocities used by the eyes. These constraints have been attributed either to
neurally generated commands or to the physical mechanics of the eye and its surrounding muscles and tissues (i.e., the ocular plant). To
directly test whether the ocular plant implements the half-angle rule, critical to the maintenance of Listing's law, we microstimulated the
abducens nerve with the eye at different initial vertical eye positions. We report that the electrically evoked eye velocity exhibits the same
eyepositiondependenceasseeninvisuallyguidedsmooth-pursuiteyemovements.Theseresultssupportanimportantrolefortheocular
plant in providing a solution to the degrees-of-freedom problem during eye movements.
Key words: eye; torsion; muscles; pulleys; Listing's law; pursuit
Introduction
Our limbs are controlled in the presence of kinematic redun-
dancy. For example, when pointing to an object, one can rotate
the arm torsionally about the index finger and still remain point-
ing at the same object. Similarly, the oculomotor system also faces
kinematic redundancy during visually guided eye movements:

  

Source: Angelaki, Dora - Department of Anatomy and Neurobiology, Washington University in St. Louis

 

Collections: Biology and Medicine