A model of the optokinetic reflex system in larval Xenopus
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1
Clinical Neurosciences, Ludwig-Maximilians-University, Center for Sensorimotor Research, Germany
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2
Ludwig-Maximilians-University, Department Biology II, Germany
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3
Klinikum Großhadern, Ludwig-Maximilians-University, DFG Research Training Group 1091, Germany
Vestibular and optokinetic reflexes are classically considered to be the major contributors for maintaining visual acuity during locomotion in vertebrates. Here, we present a computational model of the optokinetic reflex system, which helps to elucidate the functional organization and sensory-motor processing within the neural circuitry responsible for the visual image stabilizing system in Xenopus laevis. The optokinetic reflex performance was tested by various step and sinusoidal visual stimulus patterns, which were presented by rotation of a vertically striped drum in semi-intact preparations of larval Xenopus with a functional visual system. Eye movements were studied by computer analysis of videos recorded from the animals during optokinetic stimulation with a camera at 50 frames per second. The optokinetic response of larval Xenopus consisted of slow following phases, which were regularly interrupted by resetting fast phases. The horizontal ocular motor range was ~60° and the maximal gain was 0.63 ± 0.03 at 2°/s constant rotation. Miniature oscillations with a frequency of 2.78 ± 0.39 Hz could be observed during the slow phases independent of stimulation velocity. Simultaneous motion recordings of one eye and multiple-unit recordings of the contralateral lateral rectus nerve during optokinetic stimulation revealed the presence of distinct motoneuronal subgroups that were differentially active during slow and fast phases, respectively. Based on these data a computational model of the optokinetic reflex circuitry was established, simulating the interaction of the separate neuronal subgroups involved in generating the optokinetic responses on a systems level with integrating structures responsible for both slow and fast phases. The individual subsystems were approximated by gain elements and their dominant time constants, omitting further temporal characteristics. This allowed studying the dynamic behavior of the interaction between the optokinetic subsystems. Besides allowing simulations of new stimulation patterns that can be tested experimentally, the model also supports a potential task-dependent activation of separate motoneuronal subgroups for slow and fast phases, converging at the mechanical properties of the eyeball. The experimentally measured miniature oscillations emerged as an intrinsic property of the underlying model structure incorporating visual feedback pathways and uncompensated propagation delays, suggesting that the observed oscillations most likely originate from delays in the sensory transduction process. Extension of the computational model will provide further understanding about the nature of neuronal projections and adaptive changes of the optokinetic system during ontogeny. Moreover, it allows formalizing hypotheses on oculomotor behavior and eco-physiological plasticity that can be tested by experimental manipulations.
Keywords:
computational model,
optokinetic reflex,
Xenopus
Conference:
Bernstein Conference 2012, Munich, Germany, 12 Sep - 14 Sep, 2012.
Presentation Type:
Poster
Topic:
Motor control, movement, navigation
Citation:
Knorr
AG,
Schuller
JM,
Straka
H and
Glasauer
S
(2012). A model of the optokinetic reflex system in larval Xenopus.
Front. Comput. Neurosci.
Conference Abstract:
Bernstein Conference 2012.
doi: 10.3389/conf.fncom.2012.55.00146
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Received:
11 May 2012;
Published Online:
12 Sep 2012.
*
Correspondence:
Mr. Alexander G Knorr, Clinical Neurosciences, Ludwig-Maximilians-University, Center for Sensorimotor Research, Munich, Germany, knorr@mytum.de