Three-dimensional vestibular eye and head reflexes of the chameleon: characteristics of gain and phase and effects of eye position on orientation of ocular rotation axes during stimulation in yaw direction.
We investigated gaze-stabilizing reflexes in the chameleon using the three-dimensional search-coil technique. Animals were rotated sinusoidally around an earth-vertical axis under head-fixed and head-free conditions, in the dark and in the light. Gain, phase and the influence of eye position on vestibulo-ocular reflex rotation axes were studied. During head-restrained stimulation in the dark, vestibulo-ocular reflex gaze gains were low (0.1-0.3) and phase lead decreased with increasing frequencies (from 100 degrees at 0.04 Hz to < 30 degrees at 1 Hz). Gaze gains were larger during stimulation in the light (0.1-0.8) with a smaller phase lead (< 30 degrees) and were close to unity during the head-free conditions (around 0.6 in the dark, around 0.8 in the light) with small phase leads. These results confirm earlier findings that chameleons have a low vestibulo-ocular reflex gain during head-fixed conditions and stimulation in the dark and higher gains during head-free stimulation in the light. Vestibulo-ocular reflex eye rotation axes were roughly aligned with the head's rotation axis and did not systematically tilt when the animals were looking eccentrically, up- or downward (as predicted by Listing's Law). Therefore, vestibulo-ocular reflex responses in the chameleon follow a strategy, which optimally stabilizes the entire retinal images, a result previously found in non-human primates.
Haker
H
H
Neurology Department, University Hospital of Zürich, 8091 Zürich, Switzerland. haker@bli.unizh.ch
Misslisch
H
H
Ott
M
M
Frens
M A
MA
Henn
V
V
Hess
K
K
Sándor
P S
PS
D000222:Adaptation, Physiological; D000818:Animals; D003624:Darkness; D004585:Electrooculography; D005133:Eye Movements / Q000502:physiology*; D006257:Head / Q000502:physiology*; D019416:Head Movements / Q000502:physiology*; D008027:Light; D008116:Lizards; D009039:Motion Perception; D009799:Ocular Physiological Phenomena; D009949:Orientation / Q000502:physiology*; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D012399:Rotation; D013997:Time Factors