Detection of rotating gravity signals

Abstract

It is shown in the preceding paper that neurons with two-dimensional spatio-temporal properties to linear acceleration behave like one-dimensional rate sensors: they encode the component of angular velocity (associated with a rotating linear acceleration vector) that is normal to their response plane. During off-vertical axis rotation (OVAR) otolith-sensitive neurons are activated by the gravity vector as it rotates relative to the head. Unlike "one-dimensional" linear accelerometer neurons which exhibit equal response magnitudes for both directions of rotation, "two-dimensional" neurons can be shown to respond with unequal magnitudes to clockwise and counterclockwise off-vertical axis rotations. The magnitudes of the sinusoidal responses of these neurons is not only directionally selective but also proportional to rotational velocity. Thus, responses from such "two-dimensional" neurons may represent the first step in the computations necessary to generate the steady-state eye velocity during OVAR. An additional step involving a nonlinear operation is necessary to transform the sinusoidally modulated output of these neurons into a signal proportional to sustained eye velocity. Similarly to models of motion detection in the visual system, this transformation is proposed to be achieved through neuronal operations involving mathematical multiplication followed by a leaky integration by the velocity storage mechanism. The proposed model for the generation of maintained eye velocity during OVAR is based on anatomical and physiological properties of vestibular nuclei neurons and capable of predicting the experimentally observed steady-state characteristics of the eye velocity.

Two-dimensional coding of linear acceleration and the angular velocity sensitivity of the otolith system

“…An additional nonlinear step is necessary to "rectify" these sinusoidal responses and produce the observed steady-state change in the neuronal firing rate during OVAR (Benson et al 1970). The accompanying paper (Angelaki 1992b) suggests a biologically plausible mechanism for this "rectification".…”

“…The rest of this presentation will describe how the rotational velocity co is encoded by "two-dimensional" neurons. The accompanying paper (Angelaki 1992b) will explain how co could be extracted and transformed into a neural command proportional to +__ co for the generation of the steady-state eye velocity response during OVAR (see 8 in Angelaki 1992b). The first part of this section will briefly describe the response of "one-dimensional" neurons during clockwise (CW) and counterclockwise (CCW) OVAR.…”

“…The required additional step can be realized by a second-order nonlinearity, as suggested for motion detection in the visual system (Reichardt 1961;van Santen and Sperling 1985). A detailed model for the generation of the "bias" eye velocity during OVAR utilizing the responses from "two-dimensional" neurons is presented in the accompanying paper (Angelaki 1992b).…”

Fos expression in otolith‐related brainstem neurons of postnatal rats following off‐vertical axis rotation

“…With OVAR, utricular hair cells detect not only head tilts relative to gravity but also translational movements (Angelaki, 1992). The ability of the brain to resolve this tilt-translation ambiguity is critical for an accurate representation of spatial orientation and elicitation of appropriate sensorimotor reflexes (Angelaki et al, 1999;Wood, 2002).…”

Spinning versus Wobbling: How the Brain Solves a Geometry Problem

“…As an alternative to the internal model hypothesis, other authors (Hain, 1986;Raphan and Sturm, 1991;Angelaki, 1992;Raphan and Cohen, 2002) have proposed that the spin VOR measured during OVAR is produced by filtering otolith signals. However, these models predict that the otolith activation during cone motion, being identical with the activation during OVAR, should produce the same spin VOR, in contradiction with our results.…”