Eye movements during voluntary head motion with minimized cervical input.

Eye movements were recorded using DC-electro-oculography in 20 healthy subjects during sinusoidal voluntary head movements and during similar voluntary head movements with minimized cervical input. The eye movements during these conditions were compared to the vestibulo-ocular reflex (VOR), to the cervico-ocular reaction (COR) and to the active COR (i.e., voluntary stabilization of the head in space while the trunk was moved sinusoidally). Each subject sat with eyes covered on a rotating chair. Sinusoidal movements having an amplitude of +/- 20 degrees and either 0.1 or 0.2 Hz were performed. Voluntary head movements and head movements with minimized cervical input showed no difference in the gain of the slow-phase velocity of the nystagmus, the saccadic activity (cumulated amplitude/time) and the maximum eye deviation. The distribution of saccades around the reversal of head movement in space represents the only significant difference between these conditions. While the saccades appear promptly after reversal during sinusoidal voluntary head movement, they appear during voluntary head movement with minimized cervical input just before the reversal of head movement in space. The direction of saccades always depends on the displacement of the head related to the trunk and is due to cervical input and/or central influences.