A modification of eye-head coordination by CNS disease

When a subject, seated and facing ahead, was asked to look toward one side, the result was a combined movement of the eyes and head. Normal subjects began the eye movement just before the onset of head movement; 4 neurologic patients who showed abnormalities in eye movements (saccades that tended to be smaller in amplitude and lower in velocity than those of the control subjects) regularly began eye movement after the onset of head movement. Thus the initiation of the head rotation was not as much retarded in these patients as that of eye movement. Amplitudes of the movements were reduced in the patients, but this change too was less for the head than for the eyes. Because the amplitude and velocity of the head movement were less affected in the patient group, the relative contribution of the head to the total gaze shift was increased. It appears as if, when the oculomotor system is affected, the head can assume a leading role in the initiation and execution of gaze shifts.