Mechanisms of Interrupted Saccades Differ in Normal Subjects and Late Onset Tay-Sachs Patients

Saccades normally occur in one smooth movement. In late-onset Tay-Sachs disease (LOTS), saccades have initial normal acceleration, but are interrupted by a transient deceleration greater than that at normal saccade end. Before eye velocity reaches zero, it reaccelerates and goes to target. These saccades are similar to those seen when monkey omnipause neurons are stimulated at saccade onset. Two-step saccades are occasionally seen in normal subjects.