RAPID COMMUNICATION Hypothesis for Shared Central Processing of Canal and Otolith Signals

Green, Andrea M. and Henrietta L. Galiana. Hypothesis for cies above Ç0.5 Hz (Paige and Tomko 1991a; Paige et shared central processing of canal and otolith signals. J. Neuroal. 1996; Tokita et al. 1981). Third, the appropriate ocular physiol. 80: 2222–2228, 1998. A common goal of the translational compensation for a pure head translation depends inversely vestibuloocular reflex (TVOR) and the rotational vestibuloocular on target distance so that ideally no response is required in an reflex (RVOR) is to stabilize visual targets on the retinae during unconverged state (Busettini et al. 1994; Paige and Tomko head movement. However, these reflexes differ significantly in 1991b; Schwarz and Miles 1991; Telford et al. 1997). Hence their dynamic characteristics at both sensory and motor levels, TVOR performance must be interpreted in conjunction with implying a requirement for different central processing of canal binocular viewing context. In comparison, although the reand otolith signals. Semicircular canal afferents carry a signal proquired RVOR gain also depends on target location (Crane portional to angular head velocity, whereas primary otolith afferents modulate approximately in phase with linear head acceleration. et al. 1997; Hine and Thorn 1987; Snyder and King 1992; Behaviorally, the RVOR exhibits a robust response down toÇ0.01 Viirre et al. 1986), its performance is easily gauged relative Hz, yet the TVOR is only significant above Ç0.5 Hz. Several to an ideal gain of 1 for far target viewing. hypotheses were proposed to address central processing in the Recent studies provided better behavioral descriptions of TVOR pathways. All rely on a central filtering process that prethe TVOR by taking into account both frequency range and cedes a ‘‘neural integrator’’ shared with the RVOR. We propose target location (Paige et al. 1996; Telford et al. 1997). Yet, an alternative hypothesis for the convergence of canal and otolith little is known about how and where sensory otolith signals signals that does not impose the requirement for additional loware processed centrally. Relatively few studies considered pass filters for the TVOR. The approach is demonstrated using an central responses during pure linear translation, and in genanatomically based, simple model structure that reproduces the eral either observed responses were not correlated with ocugeneral dynamic characteristics of the RVOR and TVOR at both ocular and central levels. Differential dynamic processing of otolith lar behavior (Angelaki et al. 1993; Bush et al. 1993; Lannou and canal signals is achieved by virtue of the location at which et al. 1980), or the cells described could not be specifically sensory information enters a shared but distributed neural interelated to well-known vestibuloocular cell types in the vesgrator. As a result, only the RVOR is provided with compensation tibular nuclei (VN) (Perachio 1981; Xerri et al. 1987). Refor the eye plant. Hence canal and otolith signals share a common cently, neuronal responses to translation during eccentric central integrator, as in previous hypotheses. However, we propose vertical-axis rotation were isolated from angular response that the required additional filtering of otolith signals is provided components by comparing on-axis and off-axis responses. by the eye plant. The well-characterized position-vestibular-pause (PVP) and