Optokinetic and Vestibular Stimulation Determines the Spatial Orientation of Negative Optokinetic Afternystagmus in the Rabbit

Abstract

Prolonged binocular optokinetic stimulation (OKS) in the rabbit induces a high-velocity negative optokinetic afternystagmus (OKAN II) that persists for several hours. We have taken advantage of this uniform nystagmus to study how changes in static head orientation in the pitch plane might influence the orientation of the nystagmus. After horizontal OKS, the rotation axis of the OKAN II remained almost constant in space as it was kept aligned with the gravity vector when the head was pitched by as much as 80 degrees up and 35 degrees down. Moreover, during reorientation, slow-phase eye velocity decreased according to the head pitch angle. Thereafter, we analyzed the space orientation of OKAN II after optokinetic stimulation during which the head and/or the OKS were pitched upward and downward. The rotation axis of OKAN II did not remain aligned with an earth vertical axis nor a head vertical axis, but it tended to be aligned with that of the OKS respace. The slow-phase eye velocity of OKAN II was also affected by the head pitch angle during OKS, because maximal OKAN II velocity occurred at the same head pitch angle as that during optokinetic stimulation. We suggest that OKAN II is coded in gravity-centered rather than in head-centered coordinates, but that this coordinate system may be influenced by optokinetic and vestibular stimulation. Moreover, the velocity attenuation of OKAN II seems to depend on the mismatch between the space-centered nystagmus rotation axis orientation and that of the "remembered" head-centered optokinetic pathway activated by OKS.

Influence of Gravity on the Spatial Orientation of Eye Nystagmus Induced by Unilateral Lesion of Horizontal Semicircular Canal

“…100% of velocity corresponds to that at 0°pitch angle. (B) OKAN II slow phase eye velocity and curves of fit (a second order polynomial), from our previous works in normal rabbits (6) and rabbits with nodulus and ventral uvula ablation (12).…”

“…However, only the velocity storage component of OKAN and PRN appears to be influenced by gravity, while direct eye responses remain fixed in head co-ordinates (5). Recently, we demonstrated that the rotation axis of steadystate negative optokinetic after-nystagmus (OKAN II) following long-lasting optokinetic stimulation also tends to align with gravity (6). The spatial constancy of OKAN II, which depends on an internal asymmetry in the visuo-vestibular circuitry (7), prompted us to examine whether the nystagmus induced by unilateral damage of the labyrinth may also be influenced by gravity.…”

Head position modulates optokinetic nystagmus

“…In addition to guiding reflexive eye movements, the combined signals modulate centrally stored eye movements such as post-rotatory vestibular nystagmus (PRN; Guedry 1965; Benson 1974; Harris 1987; Harris and Barnes 1987; Minor and Goldberg 1990; Fetter et al 1996; Merfeld et al 1993; Angelaki and Hess 1995; Wearne et al 1998; Clément 2003), positive optokinetic afternystagmus (OKAN I) (Raphan and Cohen 1988; Waespe and Henn 1978; Dai et al 1991), and negative optokinetic afternystagmus (OKAN II) (Maioli 1988; Pettorossi et al 1999). The rotational axes of OKN, PRN, OKAN I, and OKAN II change when the head changes its orientation with respect to gravity (Dai et al 1991; Merfeld et al 1993; Gizzi et al 1994; Angelaki and Hess 1995; Wearne et al 1998; Kitama et al 2004).…”

“…SPEV is attenuated when the head assumes a different position in space with respect a previously learned reference position (Pettorossi et al 1999). For example, a long-lasting OKAN is induced by optokinetic stimulation, OKAN II, during which SPEV occurs in the opposite direction of the optokinetic stimulus used to evoke it (Pettorossi et al 1999). OKAN II attains maximal velocity when the head is maintained in the position it held during horizontal optokinetic stimulation (HOKS).…”

Activity-Dependent Expression of Acyl-Coenzyme A-Binding Protein in Retinal Muller Glial Cells Evoked by Optokinetic Stimulation

“…1 D). OKAN-II lasts for tens of hours (Barmack and Nelson, 1987;Pettorossi et al, 1999;Barmack et al, 2002). The reduction in gain of the HOKR and the genesis of OKAN-II are the hallmarks of optokinetic adaptation.…”