Several studies have demonstrated the importance of the pretectal Nucl
eus of the Optic Tract (NOT) and the Dorsal Terminal Nucleus of the ac
cessory optic system (DTN) for the generation of horizontal optokineti
c nystagmus (OKN). Although single unit data from trained rhesus monke
y NOT/DTN cells are available it is still unclear if there is a link b
etween the pursuit and the optokinetic system at this level of motion
analysis. In order to address the question whether the NOT/DTN is impo
rtant for the optokinetic as well as the pursuit system an electrolyti
c lesion was placed where NOT/DTN activity was recorded previously. Th
e monkey was tested on optokinetic and pursuit paradigms. Immediately
following the lesion the monkey performed a spontaneous nystagmus with
slow phases directed away from the lesioned side. This spontaneous ny
stagmus persisted even during optokinetic stimulation in the opposite
direction. During the first week postlesion the spontaneous nystagmus
disappeared and the monkey regained the ability to perform optokinetic
nystagmus toward the lesioned side. The gain of the mean slow phase e
ye velocity was, however, largely reduced for this stimulus direction.
The onset of OKN following the onset of optokinetic stimulation was n
ot affected by the lesion. During smooth pursuit the mean eve velocity
was more reduced for pursuit towards the lesioned side. The resulting
position error was compensated by an increase in the number of catch-
up saccades. In addition to the confirmation of the well-known directi
onal deficits of the optokinetic system caused by a lesion of the pret
ectum, a directional deficit in the pursuit system was demonstrated.