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Gravity-Specific Adaptation of the Angular Vestibuloocular Reflex: Dependence on Head Orientation With Regard to Gravity
Ist Teil von
Journal of neurophysiology, 2003-01, Vol.89 (1), p.571-586
Ort / Verlag
United States: Am Phys Soc
Erscheinungsjahr
2003
Link zum Volltext
Quelle
Free E-Journal (出版社公開部分のみ)
Beschreibungen/Notizen
Departments of 1 Neurology and
2 Physiology and Biophysics, Mount Sinai School
of Medicine, New York City, 10029; and
3 Department of Computer and Information Science,
Brooklyn College of the City University of New York, Brooklyn, New
York 11210
Yakushin, Sergei B.,
Theodore Raphan, and
Bernard Cohen.
Gravity-Specific Adaptation of the Angular Vestibuloocular
Reflex: Dependence on Head Orientation With Regard to Gravity. J. Neurophysiol. 89: 571-586, 2003. The gain of the vertical angular vestibuloocular reflex (aVOR) was
adaptively altered by visual-vestibular mismatch during rotation about
an interaural axis, using steps of velocity in three head orientations:
upright, left-side down, and right-side down. Gains were decreased by
rotating the animal and visual surround in the same direction and
increased by visual and surround rotation in opposite directions. Gains
were adapted in one head position (single-state adaptation) or
decreased with one side down and increased with the other side down
(dual-state adaptation). Animals were tested in darkness using
sinusoidal rotation at 0.5 Hz about an interaural axis that was tilted
from horizontal to vertical. They were also sinusoidally oscillated
from 0.5 to 4 Hz about a spatial vertical axis in static tilt positions
from yaw to pitch. After both single- and dual-state adaptation, gain
changes were maximal when the monkeys were in the position in which the
gain had been adapted, and the gain changes progressively declined as
the head was tilted away from that position. We call this
gravity-specific aVOR gain adaptation . The spatial
distribution of the specific aVOR gain changes could be represented by
a cosine function that was superimposed on a bias level, which we
called gravity-independent gain adaptation . Maximal
gravity-specific gain changes were produced by 2-4 h of adaptation for
both single- and dual-state adaptations, and changes in gain were
similar at all test frequencies. When adapted while upright, the
magnitude and distribution of the gravity-specific adaptation was
comparable to that when animals were adapted in side-down positions.
Single-state adaptation also produced gain changes that were
independent of head position re gravity particularly in association
with gain reduction. There was no bias after dual-state adaptation.
With this difference, fits to data obtained by altering the gain in
separate sessions predicted the modulations in gain obtained from
dual-state adaptations. These data show that the vertical aVOR gain
changes dependent on head position with regard to gravity are
continuous functions of head tilt, whose spatial phase depends on the
position in which the gain was adapted. From their different
characteristics, it is likely that gravity-specific and
gravity-independent adaptive changes in gain are produced by separate
neural processes. These data demonstrate that head orientation to
gravity plays an important role in both orienting and tuning the gain
of the vertical aVOR.