Saccadic gain adaptivity in the two eyes in Wallenberg's lateral medullary syndrome

Abstract

Saccadic movements and their adaptive gain control in the two eyes were explored in six patients with an ischemic infarction in the lateral medulla oblongata (Wallenberg's syndrome). Eye movements were recorded binocularly with the search coil method to examine their conjugacy. Gain adaptivity of experimentally induced hypermetric saccades was tested with the double target step paradigm.

All patients had persistent saccadic dysmetria as compared to control subjects. The dysmetria was direction-specific and not equal in the two eyes. Ipsiversive saccades were on average by 20.5% larger than contraversive saccades. The amplitude of ipsiversive saccades was on average by 1.6% and that of contraversive saccades by 3.9% larger in the ab- than in the adducting eye, compared to 0.75% in normal subjects. There is strong evidence that gain adaptivity of horizontal saccades was diminished. The reduced capability to readjust saccadic gain to altered visual feedback was, however, equal in the two eyes. The author speculates that the observed saccadic abnormalities are caused by the functional disconnection of vermal Purkinje cells from their target cells in the fastigial nucleus, due to disruption of climbing fiber pathways in the lateral medulla.

Key Words:

• Saccade
• motor learning
• binocularity
• Wallenberg
• cerebellum