1. Visual-Vestibular Interaction Hypothesis for the Control of Orienting Gaze Shifts by Brain Stem Omnipause Neurons Mario Prsa and Henrietta L. Galiana Department of Biomedical Engineering, McGill University, Montreal, Quebec, Canada Presented by: Fereshteh Lagzi

2. Presentation Agenda Introduction Model Description Simulation Results Conclusion

3. Introduction Gaze =(eye position-in-head + head position-in-space) orienting movements of the visual axis are referred to as gaze shifts and are composed of an initial fast phase followed by a slow phase.

4. Introduction target attainment target fixation

5. Omnipause Neurons These two fundamental requirements of gaze shifts, target attainment and target fixation, are coordinated by omni-directional pause neurons (OPNs) located in the nucleus raphe interpositus of the caudal pontine reticular formation in the brain stem. OPNs discharge at a regular rate during visual fixation and pause for the duration of the saccadic gaze component.

6. Gaze Saccade Generation

7. Robinson’s Model The classic local feedback model of eye saccade generation (Robinson 1975) compares the actual eye position Theta to the desired target position ThetaT to produce a motor error signal that drives the burst cells. Improvements of Robinson’s model rely on a dynamic motor error signal produced by a “comparator” that drives the burst neurons during the saccadic fast phase. Most models either attribute its role to the superior colliculus (SC) or place it downstream of the SC.

8. Proposed Switching Strategy

9. Model Description

10. Head Brake Experiment

11. Head Velocity & Gaze Position Error

12. Gaze Shift Simulation

13. Head-Fixed Eye Saccades Simulation

14. OPN Stimulation

15. Head Brake Simulation

16. Conclusion The proposed visual-vestibular interaction controlling the activity of OPNs was shown to accurately reproduce alternations between fast and slow phases of combined eye-head gaze movements, which are not controlled uniquely by a gaze motor error signal. Inputs to the OPNs are based on a weighted premotor fusion of different signals. The presentedhypothesis for the neural control of OPNs can thus provide insight for further investigations of how the firing activity of these neurons is modulated during all types of eye-head movements.

17. References [1] Prsa M, Galiana H.L. Visual- Vestibular Interaction Hypothesis for the Control of Orienting Gaze Shifts by Brain Stem Omnipause Neurons. J Neurophysiol 97: 1149-1162, 2007 ]2[ سعيدي، ساره. سمينار درس مدلسازي سيستمهاي بيولوژيکي، دانشکده مهندسي پزشکي، دانشگاه صنعتي اميرکبير، تابستان 1386