Quantifying Utricular Stimulation During Natural Behavior

Abstract

The use of natural stimuli in neurophysiological studies has led to significant insights into the encoding strategies used by sensory neurons. To investigate these encoding strategies in vestibular receptors and neurons, we have developed a method for calculating the stimuli delivered to a vestibular organ, the utricle, during natural (unrestrained) behaviors, using the turtle as our experimental preparation. High-speed digital video sequences are used to calculate the dynamic gravito-inertial (GI) vector acting on the head during behavior. X-ray computed tomography (CT) scans are used to determine the orientation of the otoconial layer (OL) of the utricle within the head, and the calculated GI vectors are then rotated into the plane of the OL. Thus, the method allows us to quantify the spatio-temporal structure of stimuli to the OL during natural behaviors. In the future, these waveforms can be used as stimuli in neurophysiological experiments to understand how natural signals are encoded by vestibular receptors and neurons. We provide one example of the method which shows that turtle feeding behaviors can stimulate the utricle at frequencies higher than those typically used in vestibular studies. This method can be adapted to other species, to other vestibular end organs, and to other methods of quantifying head movements.

Multiscale modeling of mechanotransduction in the utricle

“…This is a very important result, but it needs to be replicated in other species. Rivera et al (2012) have recently developed a library of utricular stimulus waveforms generated during a variety of natural behaviors in the turtle (T. scripta). Given the extensive information available for the structure (see STRUCTURE) and mechanical properties (see MACROMECHANICS and MICROMECHAN-ICS: HAIR BUNDLE MOTION AND MET CURRENTS) of the utricle in this species, these waveforms can be used to develop models of the response properties of utricular afferents to natural stimuli and test hypotheses about the role that variation in the structural and mechanical properties of utricular hair cells plays in the extraction of information about head movements.…”

“…The methods for calculating the forces acting in the plane of the otoconial layer (OL) of the utricle during natural behavior have been described in detail (Rivera et al 2012). Briefly, we made high-speed (1,000 frames/s) video recordings of four separate natural movements, swimming, walking, head retraction, and feeding strikes, in three turtles, using two synchronized digital cameras.…”

An operating principle of the turtle utricle to detect wide dynamic range

“…This static head tilt is followed by a quick head motion during feeding strike. Rivera et al used fast video imaging at two different views to measure 3-D head motion during an underwater feeding strike of a turtle (Rivera, Davis et al 2012). The utricle accelerations in its three orthogonal axes was computed from the head motion.…”

“…However, three lines of recent studies shed new light on the realistic stimulations on the utricular hair cells. Rivera et al (2012) measured the head motion of an unconstrained turtle during feeding strike. Based on anatomical measurements, they calculated the acceleration vector components of the utricle from the head motion.…”

Tripping Elicits Earlier and Larger Deviations in Linear Head Acceleration Compared to Slipping

“…Tri-axial linear acceleration of the right and left vestibular organs was calculated using methods similar to Rivera et al [29]. Briefly, a head-fixed reference frame was first defined using three markers on the head (back of head, right temple, left temple).…”