The role of gravity in adaptation of the vertical angular vestibulo-ocular reflex.
The gain of the vertical angular vestibulo-ocular reflex (aVOR) was adapted in side-down and prone positions in two monkeys and tested in four planes: left-/right-side down; forward/backward; and two intermediate planes that lie approximately in the planes of the vertical semicircular canal pairs, left anterior/right posterior (LA/RP) and right anterior/left posterior (RA/LP). Gain changes, expressed as a percent of preadapted values, were plotted as a function of head orientation in the planes of tilt, and fitted with sinusoids to obtain the gravity-dependent (amplitude) and gravity-independent (bias) components of adaptation. Gravity-dependent gain changes were always maximal when tested in a plane that included the head orientation in which the aVOR gain had been adapted. Changes were minimal when the head was tilted in a plane orthogonal to the plane of adaptation, and were smaller but still significant when tested in the two intermediate planes. Gravity-independent VOR gain changes were uniform over all planes of head tilt. Thus, the gravity-dependent and gravity-independent components could be separated experimentally. The aVOR gain changes from the head tilts in different directions were utilized to reconstruct the gain changes in three dimensions. They formed a continuous surface, which peaked in and around the position of adaptation. These studies support the postulate that gain adaptation has both gravity-independent and gravity-dependent components, and further show that these gain changes have a three-dimensional structure. These results are similar to those in humans, indicating that the gravity-dependent adaptation of the aVOR is likely to be a common phenomenon across species.
Yakushin
Sergei B
SB
Department of Neurology, Box 1135, Mount Sinai School of Medicine, 1 East 100th Street, New York, NY 10029, USA. sergei.yakushin@mssm.edu
Xiang
Yongqing
Y
Raphan
Theodore
T
Cohen
Bernard
B
D000064:Acclimatization; D000221:Adaptation, Ocular; D000818:Animals; D005133:Eye Movements / Q000502:physiology; D006112:Gravitation; D019416:Head Movements / Q000502:physiology; D008252:Macaca fascicularis; D011187:Posture; D016684:Prone Position; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*