Agonist and antagonist muscle tension during horizontal saccadic eye movements.

Agonist and antagonist muscle tension simulations are reported for a fourth-order model of the oculomotor plant and active state tensions generated by a neural feedback model during horizontal saccadic eye movements. The lateral and medial rectus muscles are modeled as a parallel combination of passive elasticity, and series elasticity connected to a parallel combination of active state tension generator, viscosity element and elastic element. The eyeball is modeled as a sphere with moment of inertia connected to a viscosity element and an elastic element. The active state tension is generated by a low-pass filtered output from the neural burst circuit. The saccade generator is first-order time optimal and located in the superior colliculus. Agonist muscle tensions simulated with TUTSIM match the data extremely well. Antagonist muscle tension simulated with TUTSIM have an initial drop in tension, consistent with microelectrode predictions, and then a rise in muscle tension. The initial drop in antagonist muscle tension has not been reported in the literature because of band limitations of the force transducer used to record muscle tension.