| Abstract No.: | B-D2152 |
| Country: | Canada |
| | |
| Title: | DO VESTIBULAR AFFERENTS DIFFERENTIALLY ENCODE ACTIVE AND PASSIVE TRANSLATIONS? |
| | |
| Authors/Affiliations: | 1 Mohsen Jamali*; 1 Soroush Sadeghi Ghandehari; 1 Kathleen Cullen;
1 Department of Physiology, McGill University, Montreal, QC, Canada
|
| | |
| Content: | Objectives: The ability to distinguish sensory inputs that are a consequence of our own actions from those that result from changes in the external world is essential for perceptual stability and accurate motor control. Previous studies have shown that sensory inputs resulting from active and passive angular head movements are differentially encoded at an early stage of vestibular processing. While vestibular afferents innervating the semicircular canals encode active and passive head movements similarly, neurons in the vestibular nucleus that receive signals from these afferents do not reliably encode head velocity resulting from self-generated movements. In this study, we address the question of whether the same principle also applies to vestibular cells that encode translational movements.
Materials and Methods: To test this hypothesis, single units were recorded in the vestibular nerve of alert macaque monkeys under several conditions: 1) the cells were characterized using sinusoidal passive head movements along the vertical and horizontal axes, 2) the activity of the same cells were recorded during active translational movements that were restrained to one axis; i.e. vertical, fore-aft or interaural axis, and 3) the responses were obtained when animals were translated to induce head movements with trajectories comparable to those generated during voluntary head movements. To carry out this study, monkeys were trained to make translational head movements to follow food targets moved along one axis. A least-squares regression analysis was used to determine the bias discharge, sensitivity to head acceleration, and the phase shift of each unit relative to head acceleration,.
Results: Extracellular single unit recording were obtained from 34 afferent fibers innervating the saccule and utricle. Based on the normalized coefficient of variation of the interspike interval, our sample divided to regularly discharging (n = 21) and irregularly discharging units (n = 13). When classified based on the axis of translation that led to maximum activation during passive head-on-body translation, there were 12, 9, and 13 units sensitive to lateral, fore-aft and vertical translations respectively. The mean bias discharge measured across afferents during passive translations was 85.81 spikes/s and was 86.94 spikes/s for the active translations (paired t-test; p = 0.168). The mean acceleration sensitivity of the afferents for passive translations was 87.85 (spikes/s)/G, and the mean for active translations was 85.04 (spikes/s)/G (paired t-test; p = 0.377). There were no significant changes in afferent responses in terms of bias discharge or sensitivity to head acceleration between passive and active head translations.
Conclusion: Our data indicate that otolith afferents can not distinguish between active and passive head translations.
|
| | |
| Back |
|
