title: Modeling eye-head gaze shifts in multiple contexts without motor planning.
abstract: During gaze shifts, the eyes and head collaborate to rapidly capture a target (saccade) and fixate it. Accordingly, models of gaze shift control should embed both saccadic and fixation modes and a mechanism for switching between them. We demonstrate a model in which the eye and head platforms are driven by a shared gaze error signal. To limit the number of free parameters, we implement a model reduction approach in which steady-state cerebellar effects at each of their projection sites are lumped with the parameter of that site. The model topology is consistent with anatomy and neurophysiology, and can replicate eye-head responses observed in multiple experimental contexts: 1) observed gaze characteristics across species and subjects can emerge from this structure with minor parametric changes; 2) gaze can move to a goal while in the fixation mode; 3) ocular compensation for head perturbations during saccades could rely on vestibular-only cells in the vestibular nuclei with postulated projections to burst neurons; 4) two nonlinearities suffice, i.e., the experimentally-determined mapping of tectoreticular cells onto brain stem targets and the increased recruitment of the head for larger target eccentricities; 5) the effects of initial conditions on eye/head trajectories are due to neural circuit dynamics, not planning; and 6) "compensatory" ocular slow phases exist even after semicircular canal plugging, because of interconnections linking eye-head circuits. Our model structure also simulates classical vestibulo-ocular reflex and pursuit nystagmus, and provides novel neural circuit and behavioral predictions, notably that both eye-head coordination and segmental limb coordination are possible without trajectory planning.
authors.affiliation: Department of Biomedical Engineering, McGill University, Montreal, Quebec, Canada; and.
authors.forename: Iman
authors.initials: I
authors.lastname: Haji-Abolhassani
authors.affiliation: Department of Neurology and Neurosurgery, Montreal Neurological Institute, Montreal, Quebec, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Guitton
authors.affiliation: Department of Biomedical Engineering, McGill University, Montreal, Quebec, Canada; and henrietta.galiana@mcgill.ca.
authors.forename: Henrietta L
authors.initials: HL
authors.lastname: Galiana
mesh_terms: D000200:Action Potentials; D000818:Animals; D001933:Brain Stem / Q000033:anatomy & histology / Q000502:physiology; D002415:Cats; D002531:Cerebellum / Q000033:anatomy & histology / Q000502:physiology; D005133:Eye Movements / Q000502:physiology*; D000882:Haplorhini; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008959:Models, Neurological; D016571:Neural Networks, Computer; D009434:Neural Pathways / Q000033:anatomy & histology / Q000502:physiology; D009474:Neurons / Q000502:physiology; D017711:Nonlinear Dynamics
keywords: common error feedback; eye-head coordination; gaze shifts; network modeling; saccade and fixation; vestibular compensation