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

• Published in: Journal of Comparative Physiology 2003-07, Vol.189 (7), p.509-517
• Main Authors: Haker, H, Misslisch, H, Ott, M, Frens, M A, Henn, V, Hess, K, Sándor, P S
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological; Animals; Darkness; Electrooculography; Eye Movements - physiology; Head - physiology; Head Movements - physiology; Light; Lizards; Motion Perception; Ocular Physiological Phenomena; Orientation - physiology; Primates; Reflex, Vestibulo-Ocular - physiology; Rotation; Space life sciences; Time Factors
• ISSN: 0340-7594; 1432-1351
• DOI: 10.1007/s00359-003-0426-y

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.