Open Loop Optokinetic Responses of the Turtle (original) (raw)
Related papers
Visual Neuroscience, 1996
The turtle's optokinetic response is described by a simple model that incorporates visual-response properties of neurons in the pretectum and accessory optic system. Using data from neuronal and eye-movement recordings that have been previously published, the model was realized using algebraic-block simulation software. It was found that the optokinetic response, modelled as a simple negative feedback system, was similar to that measured from a behaving animal. Because the responses of retinal-slip detecting neurons corresponded to the nonlinear, closed-loop optokinetic response, it was concluded that the visual signals encoded in these neurons could provide sufficient sensory information to drive the optokinetic reflex. Furthermore, it appears that the low gain of optokinetic eye movements in turtles, which have a negligible velocity storage time constant, may allow stable oculomotor output in spite of neuronal delays in the reflex pathway. This model illustrates how visual neurons in the pretectum and accessory optic system can contribute to visually guided eye movements.
Ocular Kinematics Measured by In Vitro Stimulation of the Cranial Nerves in the Turtle
Journal of visualized experiments : JoVE, 2018
After animals are euthanized, their tissues begin to die. Turtles offer an advantage because of a longer survival time of their tissues, especially when compared to warm-blooded vertebrates. Because of this, in vitro experiments in turtles can be performed for extended periods of time to investigate the neural signals and control of their target actions. Using an isolated head preparation, we measured the kinematics of eye movements in turtles, and their modulation by electrical signals carried by cranial nerves. After the brain was removed from the skull, leaving the cranial nerves intact, the dissected head was placed in a gimbal to calibrate eye movements. Glass electrodes were attached to cranial nerves (oculomotor, trochlear, and abducens) and stimulated with currents to evoke eye movements. We monitored eye movements with an infrared video tracking system and quantified rotations of the eyes. Current pulses with a range of amplitudes, frequencies, and train durations were used...
Analysis of direction-tuning curves of neurons in the turtle's accessory optic system
Experimental Brain Research, 1998
Visual-movement sensitivity of neurons in the turtle's accessory optic system was investigated. Neuronal responses to stimulus direction and speed were analyzed to determine whether they reflect processing by a one-dimensional encoder of visual motion or whether they indicate directional integration of presynaptic direction-sensitive responses whose maximal-response directions are distributed. Both of these mechanisms make predictions about the functional relationship between stimulus direction and response. The responses of single units in the basal optic nucleus to visual stimulation in different directions were described by both cosine and wrapped normal fitting functions. The wrapped normal function (a Gaussian curve mapped onto a circle) performed at least as well as the cosine function and described directional tuning curves of varying widths. Unlike cosines, the addition of two wrapped normals could describe multi-lobed directional data. Next, it was demonstrated that these neurons did not encode visual motion projected onto a single, spatial axis. Responses to the projected speed along the maximal-response direction were systematically lower than responses to the actual speed along that direction. Thus, for speeds above 1/s, neuronal response varies with respect to direction but not speed. Summation of presynaptic direction-sensitive responses with distributed maximal-response directions (referred to as directional integration) is discussed as a means of accounting for these results.
Direction Tuning of Individual Retinal Inputs to the Turtle Accessory Optic System
1998
Neurons in turtle accessory optic system (basal optic nucleus (BON)) were recorded to study convergence of retinal afferents, using whole-cell patch electrodes in a reduced in vitro brain- stem preparation with the eyes attached. BON cells primarily exhibit EPSPs from a contralateral retinal ganglion cell input and generate an output of action potentials. Visual responses were evoked by different directions
Ocular Kinematics Measured by <em>In Vitro</em> Stimulation of the Cranial Nerves in the Turtle
Journal of Visualized Experiments, 2018
After animals are euthanized, their tissues begin to die. Turtles offer an advantage because of a longer survival time of their tissues, especially when compared to warm-blooded vertebrates. Because of this, in vitro experiments in turtles can be performed for extended periods of time to investigate the neural signals and control of their target actions. Using an isolated head preparation, we measured the kinematics of eye movements in turtles, and their modulation by electrical signals carried by cranial nerves. After the brain was removed from the skull, leaving the cranial nerves intact, the dissected head was placed in a gimbal to calibrate eye movements. Glass electrodes were attached to cranial nerves (oculomotor, trochlear, and abducens) and stimulated with currents to evoke eye movements. We monitored eye movements with an infrared video tracking system and quantified rotations of the eyes. Current pulses with a range of amplitudes, frequencies, and train durations were used to observe effects on responses. Because the preparation is separated from the brain, the efferent pathway going to muscle targets can be examined in isolation to investigate neural signaling in the absence of centrally processed sensory information.
Direction tuning of inhibitory inputs to the turtle accessory optic system
Journal of neurophysiology, 2001
Neurons in turtle accessory optic system (basal optic nucleus, BON) were studied to compare excitatory and inhibitory visual inputs. Using a reduced in vitro brain stem preparation with the eyes attached, previous studies only showed a monosynaptic retinal input to the BON from direction-sensitive retinal ganglion cells that share a common preferred direction. Now using an intact brain stem preparation, not only did BON neurons display inhibitory postsynaptic potentials [IPSP(C)s] spontaneously, but IPSP(C)s were also evoked by visual pattern motion, they had their polarity reversed near the chloride equilibrium potential and they were blocked by the GABA(A) antagonist bicuculline. Because excitatory postsynaptic currents had reversal potentials >0 mV, BON cells were recorded using patch electrodes filled with QX-314 or Cs+ to measure the cell's direction tuning also at that higher reversal potential. For most of the BON neurons studied, their visual excitation and inhibition...
Vertical and torsional optokinetic eye movements in the rabbit
Pflugers Archiv-european Journal of Physiology, 1972
Rabbits were placed inside a striped drum, which was rotated at selected constant speeds around the animal's sagittal or bitemporal axis. Eye position was recorded by means of the scleral search coil system. A regular vertical or rotatory optokinetic nystagmus (OKN) was constantly obtained. The ratioslow phase eye velocity/drum velocity (=gain) amounted to 0.7–0.9 for stimulus velocities up to 1°/sec, and declined progressively for higher stimulus velocities. The overall input-output relations for torsional and vertical OKN were very similar to those found previously for horizontal OKN. Upward and downward motion were equally effective as a stimulus for each eye apart. The same was true for nasal and temporal rotation. In darkness, rotatory and vertical drift of the eye was seen, as described before for the horizontal plane. These findings support the hypothesis that the OKN system stabilizes the eyes on the (non-rotating) visual surroundings. It is proposed that vertical, torsional as well as horizontal OKN are mediated by sub-sets of similar retinal direction-selective cells as described in the literature.
Connectivity of the turtle accessory optic system
Brain Research, 2003
Recent whole-cell recordings show that there are multiple synaptic inputs to the accessory optic system of the pond turtle Pseudemys scripta elegans (the basal optic nucleus, BON), suggesting a complex role in visual processing. The BON outputs have now been investigated using transport of diI, rhodamine-conjugated and biotinylated dextrans. Although transport was primarily anterograde, contralateral retinal ganglion cells were labeled retrogradely, confirming that the injection site was a retinal target. Other retrogradely labeled neurons were found ipsilateral to the injection site, in the pretectum, the ventral tegmentum, the dorsal nucleus of the posterior commissure and the lateral habenular nucleus. However, other data indicate that the habenular cells were labeled by spread of the tracer from the BON to the adjacent fasciculus retroflexus and interpeduncular nucleus. Anterogradely labeled fibers projected from BON following three paths, a lateral bundle to the ipsilateral dorsal midbrain, an intermediate bundle to the ipsilateral pretectal area or the posterior commissure and a ventral fiber bundle to the tegmentum bilaterally. Some of these fibers projected caudally through the tegmentum and cerebellar peduncle to terminate just below the Purkinje cell layer of the cerebellar cortex. Fibers that coursed via the intermediate bundle to the posterior commissure were also seen reaching the contralateral pretectal area and the contralateral BON. Injections of the retrograde tracer Fluorogold were also made in the BON to confirm the reciprocal connectivity of both basal optic nuclei. The pathways revealed by these experiments indicate the existence of multiple afferent and efferent connections of the BON, supporting the view that the accessory optic system is more than a simple relay of retinal signals into the brainstem for optokinetic reflexes.