Behavior of Cells Without Eye Movement Sensitivity in the Vestibular Nuclei During Combined Rotational and Translational Stimuli

A total of 74 neurons that lacked eye movement sensitivity were recorded within the confines of the rostral medial and medial lateral vestibular nuclei. Of these, 36 had response characteristics that were consistent with combined canal and otolith inputs (CAOT neurons), 18 received canal inputs only (CA neurons), and 20 had otolith inputs only (OT neurons). Responses were measured during both rotational and combined rotational and translational stimuli at 0.5 and 3.0 Hz. The otolith signal was found to lag acceleration markedly at both frequencies. Indeed, one subset of CAOT neurons had otolith responses that led translational velocity by only 12° at 0.5 Hz. All translation-responsive neurons decreased their phase lag with respect to acceleration when the stimulus frequency was increased and exhibited a large increase in sensitivity. As these cells have response dynamics that lie between those seen in otolith afferents and those required to drive the motoneurons during the translational VOR, they may represent an intermediate stage in the signal processing.