Effects of unilateral midbrain lesions on gaze (eye and head) movements

The rostral midbrain, especially the rostral interstitial nucleus of the medial longitudinal fasciculus (RIMLF) and the interstitial nucleus of Cajal (INC), plays an important role in the control of eye movements. Although the effect of midbrain lesions on eye movements is well investigated, little is known about its effect on head movements. In this study, we measured eye and head (gaze) movements in five patients with unilateral, acute midbrain lesions and nine healthy controls. In all patients, vertical eye velocity was reduced as a result of the lesion compared to healthy subjects, whereas peak head velocity was not affected. Further, most patients displayed an increased contralesional torsion in peripheral head positions, independently of whether they presented a head tilt in the straight-ahead position or not. Our results indicate that midbrain lesions affect the control of eye and head differently and independently.