The vestibular sensory apparatus and associated vestibular nuclei are generally thought to encode angular head velocity during our daily activities. However, in addition to direct inputs from vestibular afferents, the vestibular nuclei receive substantial projections from cortical, cerebellar, and other brainstem structures. Given this diversity of inputs we asked: how are the responses of vestibular nuclei neurons to head velocity modified by these additional inputs during naturally occurring behaviours? Here we have focused on three specific classes of neurons in the vestibular nuclei: (1) vestibular-only (VO) neurons which are thought to mediate, at least in part, the vestibulocollic reflex (VCR); (2) position-vestibular-pause (PVP) neurons which mediate the vestibuloocular reflex (VOR), and; (3) eye-head (EH) neurons, which are thought to mediate pursuit eye movements. / We first characterized neuronal responses to passive rotation in the head-restrained condition, and then released the head to record the discharges of the same neurons during self-generated head movements. VCR interneurons (VO neurons) faithfully transmitted head velocity signals during passive head motion, but their responses were greatly attenuated during all behaviours during which the monkey's behavioral goal was to move its head relative to the body. Moreover, the attenuation occurs only when neck proprioceptive inputs match those predicted by the neck motor command. We propose that the sensory-motor matching is meditated by interconnections with the cerebellum. Our findings indicate that the VCR is suppressed during active head movements, but remains responsive to unexpected head perturbations. In contrast, VOR interneurons (PVP neurons) faithfully transmitted head velocity signals when the animal stabilized its gaze, regardless of whether the head motion was actively or passively generated; their responses were attenuated only when the monkey's behavioral goal was to redirect its axis of gaze relative to space. We propose that efference copies of oculomotor/gaze commands are responsible for the behaviourally dependent modulation of PVP neurons (and by extension the VOR) during gaze redirection. Finally, the activity of EH neurons was recorded during head-restrained smooth pursuit and eye-head gaze pursuit. EH neurons were not influenced by error terms and their activity was best described by an eye movement-based model. In addition, during gaze pursuit EH neurons were found to encode gaze and head movement-related signals. Furthermore, neuron responses could be predicted by their head movement sensitivity during passive whole-body rotation in the dark and gaze movement sensitivity during smooth pursuit, regardless of the stimulation condition. We propose that EH neuron responses reflect the summation of head movement information fro
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.84430 |
| Date | January 2002 |
| Creators | Roy, Jefferson Edward |
| Contributors | Cullen, Kathleen E. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Aerospace Medical Research Unit.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001973888, proquestno: AAINQ88574, Theses scanned by UMI/ProQuest. |
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