A Unifying Hypothesis for both Pendular and Jerk Waveforms in Infantile Nystagmus Embodied in a Behavioral Ocular Motor System Model

摘要

The original behavioral Ocular Motor System (OMS) model for Infantile Nystagmus Syndrome (INS) simulated the responses of individuals with several pendular (P) waveforms based on a hypothesized exacerbation of the normal pursuit-subsystem instability and its interaction with other OMS components. The simulation of jerk (J) waveforms and the easy transition between J and P waveforms were not included in that model. To expand this behavioral model, we intend to incorporate J waveforms with a unifying mechanism for both types of INS waveforms. The transition from a P to a J waveform required that braking saccades become foveating saccades. That simple change produced an alternating-direction J waveform. To convert it into a unidirectional-jerk waveform, the underlying pendular oscillation frequency of the model was varied and the oscillation reset with each foveating saccade. The result was a unidirectional J waveform. The use of a resettable neural integrator in the pursuit pre-motor circuitry enabled the resetting. Other functional blocks within the OMS model were also modified. The fixation subsystem remained responsible for elongating foveation periods in J and P waveforms. The simulations of this robust behavioral OMS model demonstrate that both P and J waveforms can be generated by the same pursuit-system instability; this supports the hypothesis that most INS waveforms are due to a loss of pursuit-system damping. Modeling OMS dysfunction continues to provide valuable insight into the functional structure of the OMS under both normal and pathological conditions.