The optokinetic response in wild type and white zebra finches

Optic flow is a main source of information about self movement and the three-dimensional composition of the environment during locomotion. It is processed by the accessory optic system in all vertebrates. The optokinetic response is elicited by rotational optic flow, e.g. in a rotating drum lined with vertical stripes. We investigated here the effect of rotational optic flow on the optokinetic response in wild type and white zebra finches. The highest stimulus velocity eliciting an optokinetic response (upper velocity threshold) was dependent on stimulus direction and illumination level, but was not different between the colour morphs. The upper velocity threshold was higher with temporal to nasal movements in monocularly exposed birds and symmetrical with binocular exposure. Its increase with illumination level followed Fechner's law and reached a plateau at about 560 Lux. In bright daylight, white birds did not show optokinetic responses. We conclude that the altered wiring of the visual system of white birds has no influence on accessory optic system function. The unwillingness of white birds to respond with optokinetic response in bright daylight may be due to a substantial lack of inhibition within the visual system as demonstrated earlier, which may enhance the sensibility to glare.     

家兔的开环及闭环视动震颤（OKN）研究

研究了家兔闭环及开环状态的ＯＫＮ反应。闭环时,ＯＫＮ眼动速度与刺激速度成正比,增益接近１。当固定受刺激眼形成开环状态时,ＯＫＮ眼动速度远大于刺激速度,增益可达１０２左右,说明ＯＫＮ系统是由运动跟踪的负反馈机制控制的;刺激范围缩小则眼动反应减弱,表明ＯＫＮ系统对运动信息具有空间总和作用;以视野中不同高度的局部刺激时,发现视网膜中央视带比周边部对ＯＫＮ刺激的敏感性高;单光点刺激视带中央可诱发出清楚的ＯＫＮ反应,这为临床上应用ＯＫＮ客观测定视网膜功能和运动感知提供了可能性。     

运动图形刺激时家兔的视动震颤反应

旨在用实验方法研究家兔的视动震颤（ＯＫＮ）眼动特点以及单侧前庭迷路损伤对ＯＫＮ的影响,结果表明：单眼刺激时,家兔的ＯＫＮ反应存在着从颞侧到鼻侧方向的方向优势;恒定速度刺激时,刺激开始后,家兔的ＯＫＮ眼动跟踪速度具有从小到大最后趋于稳态的建立过程,刺激消失后,存在眼动速度由大到小直到消失的视动后震颤（ＯＫＡＮ）反应,这两个过程反应了ＯＫＮ系统中可能存在速度存储机制及其对ＯＫＮ眼动的控制作用;单侧前庭     

Development of optokinetic neuronal responses in the pretectum and horizontal optokinetic nystagmus in unilaterally enucleated rats

Responses of single units to constant-velocity rotations of the visual surround (0.25-10 degrees/s) were studied in the pretectum of unilateral enucleated rats at different ages. Enucleation was performed either in the first postnatal week ("early" enucleated rats) or in the adult stage ("late" enucleated rats). Pretectal unitary responses were recorded in early enucleated animals at postnatal day 20-21, 36-49 and, in both experimental groups, in the adult stage. Optokinetic ocular nystagmus was studied in early and late enucleated rats in the adult stage. Gain of optokinetic nystagmus in temporo-nasal stimulus direction was not changed for visual surround rotations of up to 20 degrees/s compared to controls in monocular viewing conditions. At higher stimulus velocities, however, the gain dropped. In naso-temporal stimulus direction, optokinetic nystagmus was improved in gain for optokinetic pattern motions of up to 5-10 degrees/s. There were only minor differences in the gain behaviour of optokinetic nystagmus obtained from early or late enucleated rats. The optokinetic responses of pretectal neurons obtained from early and late enucleated rats were reduced in sensitivity by more than 50%. The response patterns of neurons recorded in the contralateral pretectum relative to the intact eye were shifted by a large amount from directional selective to directional nonselective response types. No such changes were obtained in the ipsilateral pretectum. In contrast to normal rats, there were very few directional selective units responding to temporo-nasal pattern motion. On the other hand, a large proportion of directional selective units responded to naso-temporal pattern motion. These latter units were found in both early and late enucleated rats. A similar response type has previously been described for intact young rats but not for adult rats. The velocity tuning curve of pretectal units studied in the adult stage was similar in shape in early and late enucleated rats and resembled that obtained from enucleated or intact young animals. Our results show that response sensitivity, direction and velocity tuning of pretectal units depend crucially on retinal afferent input originating from both eyes. The data suggest that the response characteristics of many of the pretectal units that are considered to be important for mediating optokinetic reflexes depend on interpretectal signal processing using commissural connections. There is very little evidence for an adaptative structural plasticity of the optokinetic system following loss of one eye. The reduced asymmetry observed in gain of optokinetic responses correlated in both early and late enucleated rats with the shifts observed in the distribution of pretectal unitary response patterns.     

Gain of the ventilatory exercise stimulus: definition and meaning

The ratio G = delta VE/delta VCO2 where delta VA is change in ventilation and delta VCO2 is change in CO2 production, is often used to quantitate the ventilatory response to exercise and is the overall system gain (G). However, the actual variable of interest often is the gain for the exercise stimulus (GEX). Exercise stimulus refers to a stimulus or group of stimuli other than the mean levels of arterial PO2 (PaCO2), PCO2 (PaCO2), and pH (pHa) that act to increase ventilation during exercise. GEX will be equal to G only if the response to exercise is precisely isocapnic, normoxic, and without metabolic acidosis. A mathematical model was used to examine the relationship between G and GEX when 1) the response to exercise is not strictly isocapnic and 2) when the resting PaCO2 is shifted away from its normal value. It was found that 1) when the exercise response was not strictly isocapnic, G was a poor estimate of GEX and 2) when resting PaCO2 was changed while GEX wa assumed to remain constant, G was a function of the resting PaCO2. However, this dependence of G on resting PaCO2 is a system property that was caused by the nonlinear properties of the gas exchange processes and was not a fundamental property of the controller. It is concluded that G may not always be a good estimate of GEX and may lead to incorrect conclusions concerning the nature of the exercise stimulus.     

Frame of reference transformations in motion perception during smooth pursuit eye movements

Smooth pursuit eye movements change the retinal image velocity of objects in the visual field. In order to change from a retinocentric frame of reference into a head-centric one, the visual system has to take the eye movements into account. Studies on motion perception during smooth pursuit eye movements have measured either perceived speed or perceived direction during smooth pursuit to investigate this frame of reference transformation, but never both at the same time. We devised a new velocity matching task, in which participants matched both perceived speed and direction during fixation to that during pursuit. In Experiment 1, the velocity matches were determined for a range of stimulus directions, with the head-centric stimulus speed kept constant. In Experiment 2, the retinal stimulus speed was kept approximately constant, with the same range of stimulus directions. In both experiments, the velocity matches for all directions were shifted against the pursuit direction, suggesting an incomplete transformation of the frame of reference. The degree of compensation was approximately constant across stimulus direction. We fitted the classical linear model, the model of Turano and Massof (2001) and that of Freeman (2001) to the velocity matches. The model of Turano and Massof fitted the velocity matches best, but the differences between de model fits were quite small. Evaluation of the models and comparison to a few alternatives suggests that further specification of the potential effect of retinal image characteristics on the eye movement signal is needed.     

Two-dimensional coding of linear acceleration and the angular velocity sensitivity of the otolith system

There exist otolith-sensitive vestibular nuclei neurons with spatio-temporal properties that can be described by two response vectors that are in temporal and spatial quadrature. These neurons respond to the component of a stimulus vector on a plane rather than a single axis. It is demonstrated here that these two-dimensional linear accelerometer neurons can function as one-dimensional angular velocity detectors. The two-dimensional property in both space and time allows these neurons to encode the component of the stimulus angular velocity vector that is normal to the plane defined by the two response vectors. The angular velocity vector in space can then be reconstructed by three populations of such neurons having linearly independent response planes. Thus, we propose that these two-dimensional spatio-temporal linear accelerometer neurons, in addition to participating in functions of the otolith system that are based on detection of linear acceleration, are also involved in the generation of compensatory ocular responses during off-vertical axis rotations.     

Effect of adequate stimulation on the discharge pattern of an isolated frog muscle spindle

Discharges from an isolated frog muscle spindle during mechanical stimulation of varied amplitude, velocity, and shape were investigated. The firing rate during a linear increase in strength of the stimulus is determined by its amplitude, whereas the change in firing rate is determined by the rate of increase of amplitude. With sinusoidal stimulation the firing rate apparently reproduces stimulus shape, i.e., the muscle spindle is sensitive not only to amplitude and velocity, but also to acceleration of the stimulus. Sensitivity to acceleration is most probably due to the change in threshold of appearance of action potentials observed during variation of the speed of stretching.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 426–433, July–August, 1976.     

Visual contributions to human self-motion perception during horizontal body rotation

It is still an enigma how human subjects combine visual and vestibular inputs for their self-motion perception. Visual cues have the benefit of high spatial resolution but entail the danger of self motion illusions. We performed psychophysical experiments (verbal estimates as well as pointer indications of perceived self-motion in space) in normal subjects (Ns) and patients with loss of vestibular function (Ps). Subjects were presented with horizontal sinusoidal rotations of an optokinetic pattern (OKP) alone (visual stimulus; 0.025-3.2 Hz; displacement amplitude, 8 degrees) or in combinations with rotations of a Bárány chair (vestibular stimulus; 0.025-0.4 Hz; +/- 8 degrees). We found that specific instructions to the subjects created different perceptual states in which their self-motion perception essentially reflected three processing steps during pure visual stimulation: i) When Ns were primed by a procedure based on induced motion and then they estimated perceived self-rotation upon pure optokinetic stimulation (circular vection, CV), the CV has a gain close to unity up to frequencies of almost 0.8 Hz, followed by a sharp decrease at higher frequencies (i.e., characteristics resembling those of the optokinetic reflex, OKR, and of smooth pursuit, SP). ii) When Ns were instructed to "stare through" the optokinetic pattern, CV was absent at high frequency, but increasingly developed as frequency was decreased below 0.1 Hz. iii) When Ns "looked at" the optokinetic pattern (accurately tracked it with their eyes) CV was usually absent, even at low frequency. CV in Ps showed similar dynamics as in Ns in condition i), independently of the instruction. During vestibular stimulation, self-motion perception in Ns fell from a maximum at 0.4 Hz to zero at 0.025 Hz. When vestibular stimulation was combined with visual stimulation while Ns "stared through" OKP, perception at low frequencies became modulated in magnitude. When Ns "looked" at OKP, this modulation was reduced, apart from the synergistic stimulus combination (OKP stationary) where magnitude was similar as during "staring". The obtained gain and phase curves of the perception were incompatible with linear systems prediction. We therefore describe the present findings by a non-linear dynamic model in which the visual input is processed in three steps: i) It shows dynamics similar to those of OKR and SP; ii) it is shaped to complement the vestibular dynamics and is fused with a vestibular signal by linear summation; and iii) it can be suppressed by a visual-vestibular conflict mechanism when the visual scene is moving in space. Finally, an important element of the model is a velocity threshold of about 1.2 degrees/s which is instrumental in maintaining perceptual stability and in explaining the observed dynamics of perception. We conclude from the experimental and theoretical evidence that self-motion perception normally is related to the visual scene as a reference, while the vestibular input is used to check the kinematic state of the scene; if the scene appears to move, the visual signal becomes suppressed and perception is based on the vestibular cue.     

Stimulus Deprivation Increases Pineal Gsα and Gβ

Denervation and other forms of stimulus deprivation cause an increase in the magnitude of subsequent responses, a phenomenon commonly referred to as denervation supersensitivity. This has been well demonstrated with the cyclic AMP response to norepinephrine in the pineal gland. In the present report, we address the question of whether stimulus deprivation alters alpha and beta subunits of the GTP binding regulatory protein that stimulates adenylyl cyclase activity (Gs). Stimulus deprivation of the pineal gland was produced by denervation (superior cervical ganglionectomy), decentralization of the superior cervical ganglia, or by exposure of the animal to continuous lighting. All increased both the alpha and beta subunits of Gs (Gs alpha and G beta) by up to fourfold, as estimated using semiquantitative western blot technology. These effects were detectable after 1 day of stimulus deprivation and were sustained for 2 weeks. The stimulatory effects of constant light-induced stimulus deprivation were also apparent by measuring cholera toxin-dependent ADP-ribosylation of Gs alpha, which revealed a four-fold increase in the amount of labeled substrate. The results of in vivo studies were confirmed with in vitro studies, which demonstrated a spontaneous increase in both Gs alpha and G beta during 72 h of organ culture. The constant light-induced increases in both Gs alpha and G beta were prevented by continuous administration of isoproterenol (0.3 mg/kg/day), supporting the suggestion that adrenergic stimulation controls the levels of Gs alpha and G beta. These studies indicate that stimulus deprivation increases both Gs alpha and G beta.(ABSTRACT TRUNCATED AT 250 WORDS)     

A random walk model of fast-phase timing during optokinetic nystagmus

 Most vertebrate animals produce optokinetic nystagmus in response to rotation of their visual surround. Nystagmus consists of an alternation of slow-phase eye rotations, which follow the surround, and fast-phase eye rotations, which quickly reset eye position. The time intervals between fast phases vary stochastically, even during optokinetic nystagmus produced by constant velocity rotation of a uniform surround. The inter-fast-phase interval distribution has a long tail, and intervals that are long relative to the mode become even more likely as constant surround velocity is decreased. This paper provides insight into fast-phase timing by showing that the process of fast-phase generation during constant velocity optokinetic nystagmus is analogous to a random walk with drift toward a threshold. Neurophysiologically, the output of vestibular nucleus neurons, which drive the slow phase, would approximate a random walk with drift because they integrate the noisy, constant surround velocity signal they receive from the visual system. Burst neurons, which fire a burst to drive the fast phase and reset the slow phase, are brought to threshold by the vestibular nucleus neurons. Such a nystagmic process produces stochastically varying inter-fast-phase intervals, and long intervals emerge naturally because, as drift rate (related to surround velocity) decreases, it becomes more likely that any random walk can meander for a long time before it crosses the threshold. The theoretical probability density function of the first threshold crossing times of random walks with drift is known to be that of an inverse Gaussian distribution. This probability density function describes well the distributions of the intervals between fast phases that were either determined experimentally, or simulated using a neurophysiologically plausible neural network model of fast-phase generation, during constant velocity optokinetic nystagmus. Received: 1 June 1995/Accepted in revised form: 15 February 1996     

Effect of the distance of optokinetic stimuli from the eyes on certain parameters of the optokinetic nystagmus.

The above effect was studied in 65 subjects with normal vision (mean age 20 years) in investigations in which the following factors were successively changed: distance of optokinetic stimuli from the eyes; this distance and angular velocity of stimuli; distance and frequency of stimuli or finally distance and accommodation level. The angular velocity of the pursuit nystagmus phase was found to be by far the highest and simultaneously the closest to the angular velocity of optokinetic stimuli when the latter are 1.5m from the eyes. With shorter distances, the velocity of the pursuit movements lags steadily behind that of stimulus velocity. This change is conditioned by changes in OKN amplitude since its frequency as a whole does not change. Even though the accommodation level significantly affects the velocity of the pursuit nystagmus phase, the dependence on the distance of optokinetic stimuli from the eyes persists even after atropinization. The interpretation of these findings must take into account sepcifically the demands on accommodation, convergence, and on visual attention which are increased with shorter distances.     

运图象刺动激的视动振颤(OKN)眼动反应的速度跟踪特性

本文用传统的转筒式运动条纹刺激及电视运动条纹图形刺激两种方法进行了OKN实验,对所引起的OKN反应进行了定量比较,结果证明两者的刺激效果是相似的;用电视运动图象刺激方法,分别在中心视场和周边视场进行刺激实验,阐明了OKN主要是由作用于视网膜中央区域的运动图象刺激所引起的;并对OKN的动态反应进行了实验分析,在正弦速度刺激下,OKN增益主要取决于刺激运动的加速度,而不是单纯取决于刺激运动的速度或频率,并在脉冲速度刺激的OKN实验中,用动态反应时间阐明了这一结论.     

Eye movements induced by linear acceleration in humans.

The otolith-function study is remarkably behind the semicanal-function study. In the present paper, we introduced briefly our on-going studies on eye movements including nystagmic elicitation during lateral (Gy) linear acceleration with step and sinusoidal modes using a sled-type accelerator. The eye movements were recorded by EOGs (DC) from subjects who looked at an imaginary target of their straight ahead in darkness during G-loading up to 0.5 G. Corresponding to the +Gy and -Gy segments, nystagmus and/or deviation in eye position were frequently induced in some subjects, but none or slightly in the other. The nystagmus changed the beating direction dependently on the Gy direction, while the eye-deviation could be either direction of compensatory or anticompensatory. In half of subjects, nystagmus elicitation was absent or low at 0.3 G, while it tended to increase above 0.3 G. The nystagmic elicitation was similar to each other between the both modes of acceleration, and directional preponderance (DP) was observed in some subjects. There was no correlation between the DP and the nystagmic slow-phase velocity. Functional meanings of these findings were discussed.     

Aerial and aquatic visual acuity of the grey bichir Polypterus senegalus,as estimated by optokinetic response

The present study assessed the aerial and aquatic visual abilities of juvenile grey bichir Polypterus senegalus, fish capable of terrestrial locomotion, by measuring the optokinetic response to stimuli of varying speed and spatial frequency. In water, fish tracked slow-moving (2° s⁻¹) stimuli moderately well and fast-moving stimuli very poorly. Spatial acuity was very low compared with many other species, with maximum response observed at 0.05–0.075 stimulus cycles per degree of visual arc; however, it should be noted that adult fish, with their larger eyes, are likely to have somewhat improved spatial acuity. Low spatial acuity and limited stimulus tracking ability might be expected in a nocturnal ambush predator such as P. senegalus, where gaze stabilization may be less crucial and other sensory inputs may have greater importance in perception of the environment. In air, spatial and temporal acuity were both poorer by every measure, but some visual ability persisted. As the eye shows no anatomical specialization for aerial vision, poor vision was expected; however, the large decrease in saccade velocity observed in air trials was unexpected. Stimulus parameters typically have little effect on the characteristics of the saccade, so this finding may suggest that the function of the reflex system itself could be compromised in the aerial vision of some fishes capable of terrestrial locomotion.     

Hemodynamics evoked by microelectrical direct stimulation in rat somatosensory cortex

The aim of this study was to estimate the timing (latency) of the increase in red blood cell (RBC) velocity and RBC concentration, and the magnitude of response in local cerebral blood flow (LCBF) for neuronal activation. We measured LCBF change during activation of the somatosensory cortex by direct microelectrical stimulation. Electrical stimuli of 5, 10 and 50 Hz of 1 ms pulse with 10-15 microA, were given for 5 s. LCBF, RBC velocity and RBC concentration were monitored by laser-Doppler flowmetry (LDF) in alpha-chloralose anesthetized rats (n = 7). LCBF, RBC velocity and RBC concentration increased nearly proportionally to stimulus frequency, i.e. neuronal activity. LCBF rose approximately 0.5 s after the onset of stimulation, and there was no significant time lag of the latencies among LCBF, RBC velocity and RBC concentration at the same stimulus frequency. We interpret these results to mean that the onset of LCBF increase on cortical activation is reflected by a rapid change in arteriole (resistance vessel) dilation and capillary volume. The data also elucidate the linear relationship between LCBF increase and cortical activity.     

Human optokinetic responses under quasi-open and closed loop conditions

The human optokinetic response to a horizontally moving striped pattern surrounding the subject was investigated under quasi-open and closed loop conditions. Open loop conditions were produced by the addition of an external signal from measured slow phase eye velocity to stripe velocity. A comparison of open and closed loop responses to step and sinusoidal changes of stripe velocity indicates that the central nervous system controlling slow phase optokinetic following can be described as a simple first order lag (Ka/(s+a)) where K is 4.7 and the time constant, 1/a, is 1.25 s.     

Swimming velocity of Paramecium under the conditions of weightlessness

During the 6 min-lasting "free-fall conditions" (4 x 10(-6) g) of the parabolic flight of a sounding rocket Paramecium aurelia cells showed an increase of 7.5 % in their mean swimming velocity. A detailed analysis revealed that the kinetic response was transient: after 3 min the velocity decreased to the speed of the former horizontal swimming at 1 g. Control experiments simulating the influence of vibration and hypergravity during launch of the rocket lead to the conclusion that the increase of the velocity during the parabolic flight was exclusively induced by the transition to 0 g. An increased velocity was also observed under the condition of simulated weightlessness on a fast-rotating clinostat microscope.     

The effect of saccades on threshold perception — A model study

The effect of saccadic eye movements on threshold perception is investigated theoretically. The proposed model considers eye movements by taking into account the shifting of the stimulus pattern on the retina during the occurrence of an eye movement. Saccades are characterized by high velocity and short duration. These motions cause overshoots in the response of linear filters to certain stimulus patterns. Therefore, the model predicts facilitation effects of saccades in the perception of low spatial frequency patterns and patterns flickering with high temporal frequencies. These results agree with experimentally obtained data presented in a subsequent paper. A simple approach is formulated which approximates the complex shifting function of a saccade by a switching of the pattern.     

Using light to shape chemical gradients for parallel and automated analysis of chemotaxis

Numerous molecular components have been identified that regulate the directed migration of eukaryotic cells toward sources of chemoattractant. However, how the components of this system are wired together to coordinate multiple aspects of the response, such as directionality, speed, and sensitivity to stimulus, remains poorly understood. Here we developed a method to shape chemoattractant gradients optically and analyze cellular chemotaxis responses of hundreds of living cells per well in 96‐well format by measuring speed changes and directional accuracy. We then systematically characterized migration and chemotaxis phenotypes for 285 siRNA perturbations. A key finding was that the G‐protein G_iα subunit selectively controls the direction of migration while the receptor and Gβ subunit proportionally control both speed and direction. Furthermore, we demonstrate that neutrophils chemotax persistently in response to gradients of fMLF but only transiently in response to gradients of ATP. The method we introduce is applicable for diverse chemical cues and systematic perturbations, can be used to measure multiple cell migration and signaling parameters, and is compatible with low‐ and high‐resolution fluorescence microscopy.