Deficits in torsional and vertical rapid eye movements and shift of Listing's plane after uni- and bilateral lesions of the rostral interstitial nucleus of the medial longitudinal fasciculus.

Abstract

The rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) contains burst neurons whose activity precedes rapid eye movements with a vertical and/or torsional component. To ascertain their causal role in the generation of conjugate eye movements, we placed uni- and bilateral kainic acid lesions in that region. Unilateral inactivation of the riMLF leads to a loss of all rapid eye movements with an ipsitorsional component (ipsitorsional is defined as movement of the upper pole of the ipsilateral eye in a temporal direction). Vertical eye movements are impaired in an asymmetric way, with downward movements slowed and upward movements little affected. Listing's plane is shifted in the contratorsional direction, i.e., we find a constant torsional offset for all eye positions. With bilateral lesions one observes a total loss of all vertical and torsional eye movements, while Listing's plane retains its shape and position. These results show that burst neurons in the riMLF play a decisive role in generating rapid eye movements with a vertical and torsional component.