Orientation adaptation of eye movement-related vestibular neurons due to prolonged head tilt

Abstract

Sixteen neurons, including vestibular-only (VO), eye-head velocity (EHV), and position-vestibular-pause (PVP) neurons sensitive to head tilt were recorded in the rostromedial and in superior vestibular nuclei. Projection of the otolith polarization vector to the horizontal plane (response vector orientation [RVO]) was determined before and after prolonged head orientation in side-down position. The RVO of VO neurons shifted toward alignment with the axis of gravity when the head was in the position of adaptation. PVP neurons had similar changes in RVO. There were also changes in RVO in some EHV neurons, but generally in directions not related to gravity. Modeling studies have suggested that the tendency to align RVOs with gravity leads to tuning of gravity-dependent angular vestibular ocular reflex (aVOR) gain changes to the position of adaptation. Thus, coding of orientation in PVP neurons would contribute significantly to the gravity-dependent adaptation of the aVOR.

Conflict of interest statement

Conflicts of interest

The authors have no conflicts of interest to declare.

© 2011 New York Academy of Sciences.

Figures

Figure 1

Determining RVO before and after prolonged head orientation RSD. (A) Neuronal sensitivity obtained from PVP neuron before (open symbols) and after (filled symbols) a head orientation RSD for two hours. Sensitivities (ordinate) were plotted as a function of direction of acceleration of gravity in head coordinates (abscissa). Dashed and solid curves are cosine fit through the data. Vertical lines are plotted through the peak fitted values obtained before (gray) and after (black) adaptation. Insets below approximate head orientation for corresponding accelerations of gravity. (B) Polar plot for RVO obtained for the neuron shown in (A) before (gray arrow) and after (black arrow) orientation adaptation.

Figure 2

Representative changes in RVO after orientation adaptation for PVP (A), VO (B), and EHV (C) neurons. RVO’s before adaptation are shown by gray arrows and after adaptation by black arrows.