| The long term goal of our research is to contribute to the diagnosis and treatment of disorders that affect balance and spatial orientation in humans and non-human animals. Our approach is to investigate mechanisms of balance and spatial orientation using the methods of neuroethology and an interdisciplinary team than includes neuroscientists, behavioral biologists, physicists, and engineers. Our experimental models are turtles and mice. These species offer a number of practical advantages for investigation of vestibular mechanisms. Because the vestibular system is highly conserved during evolution, knowledge gained from turtles and mice can be expected to generalize well to other vertebrates, including humans. Neuroethology is the study of neural mechanisms underlying naturally occurring behavior. Vestibular Neuroethology seeks to understand how head movements during natural behavior are converted into neural signals that can be used by the brain. This is accomplished in three steps. |
 Figure 1. Characteristic head posture of Trachemys scripta . The black iris line is aligned with a high-density band of photoreceptors and ganglion cells in the retina. During head movements, the turtle keeps its iris line parallel to earth horizontal using non-visual, probably vestibular, reflexes. |
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 Figure 2. Turtle Vestibular Organs. This laser scanning confocal micrograph shows the sensory surfaces of three vestibular organs, the utricle and the anterior and horizontal semicircular canals. To develop a broad picture of how the peripheral vestibular system works, we perform our experiments on the utricle (an otoconial organ that signals linear head motion and head orientation in space) and the canals (which signal angular head movements). |
First, we identify the spatial and temporal patterns of head movement that occur during natural behaviors using high speed digital video recordings of freely moving animals (Fig. 1). We combine these data with information about the orientation of vestibular organs in the skull to specify the pattern of stimulation that different vestibular organs experience during natural behaviors. Figure 2 illustrates the sensory surface of one otoconial organ, the utricle, and the anterior and horizontal semicircular canals. The bright green stain is phalloidin, which labels the hair bundles of vestibular hair cells (see figure 3, which illustrates major parts of a vestibular hair cell.)
Second, we use anatomical and physiological experiments and computational models, to analyze the mechanical cascade by which forces arising from head movements stimulate mechanoreceptive hair bundles on vestibular hair cells. Finally, we use experiments, models, and information analysis to determine how mechanical stimuli delivered to hair bundles are transduced into electrical signals by vestibular receptors (hair cells) and then encoded and transmitted to the brain by afferent fibers of the vestibular nerve. Figure 3 illustrates the relation between vestibular hair cells and afferents. |
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| Figure 3. Signaling stages in the vestibular periphery. Head movements create forces (1) in the inner ear that deflect hair bundles (2) on top of vestibular hair cells (3) . This deflection modulates transmitter release at the synapse (4) between hair cells and primary afferent neurons (5) , causing them to modify their firing. This modification of afferent firing is the signal (6) that the vestibular system sends to the central nervous system (CNS). The signal triggers stabilizing reflexes of eyes, trunk, and limbs. Figure 1, above, illustrates stabilization of eye orientation by vestibular reflexes. |  | |
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