To navigate and act effectively through a complex three-dimensional (3D) environment, we must accurately estimate our own motion and orientation relative to nearby objects. Although multi-modal in nature, both the perception of self-motion and self-orientation, as well as the precise monitoring of changes in our head or gaze relative to objects of interest, require contributions from the vestibular system, which provides information about the angular and linear acceleration of the head in space. The long-term goal of these studies is to understand the thalamo-cortical processing of vestibular information, pertinent to the elucidation of the neural correlates for motion perception, spatial orientation and control of movement. As a first step in delineating these unexplored neural correlates of higher vestibular processing, we propose here to characterize pre-cortical neural pathways, focusing first on the neural processing in the two main thalamic projections from the vestibular nuclei (VN) and prepositus hypoglossi (PH) to the ventral posterior nuclei (VPN) and the intralaminar nuclei (ILN) of the thalamus. Experiments proposed here are motivated by a central hypothesis where these two vestibulo-thalamic pathways participate in two distinct functions: The VPN pathway represents the conduit of vestibular signals involved in selfmotion perception. The ILN pathway, on the other hand, provides cortical eye fields with the necessary extraretinal signals (including an efference copy of gaze changes) required to update retinal information for nonretinotopic saccades. To address the validity of these hypotheses, we propose a multi-faceted approach using multiple techniques, including single unit recording, antidromic identification of physiologically-characterized neurons, dual tracer injections, as well as reversible inactivation while animals perform behavioral tasks. The proposed experiments will test for the first time a direct link between vestibular neural activities and perception and will bridge the gap between traditional vestibular system analysis and modern, functionally-relevant, stochastic correlation analysis techniques relating neural activities with animal's behavioral choices.
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