Lateralization in cats in a pointing task of the anterior limb towards a moving target]

In a group of 44 cats overtrained on a task where they had to reach for a moving target, paw performance and paw preference were investigated. More than half of the cats (n = 23) were strongly lateralized in that they used one of their paws to perform more than 90% of the reaching attempts. Among these lateralized cats, left-pawed ones (n = 17) significantly exceeded right pawed-animals (n = 6). Investigating both the accuracy and speed scores, the comparison between lateralized and non-lateralized cats (using a criterion of 90% lateralization) showed that although the accuracy scores did not differ, lateralized cats were significantly quicker to trigger their movement. No difference was found concerning the movement time. For the whole group of 44 cats the comparison between the performance levels obtained with their two forepaws showed that the more frequently used paw was significantly more accurate and faster to trigger and to execute the movement than the less used paw. This study shows that, in pointing towards a moving target, cats display an asymmetry in paw preference that is associated with a performance asymmetry.     

The influence of visual stimulation on the behaviour of cats housed in a rescue shelter

This study explored the influence of 5 types of visual stimulation (1 control condition [no visual stimulation] and 4 experimental conditions [blank television screen; and, televised images depicting humans, inanimate movement, animate movement]) on the behaviour of 125 cats housed in a rescue shelter. Twenty-five cats were randomly assigned to one of the five conditions of visual stimulation for 3 h a day for 3 days. Each cat's behaviour was recorded every 5 min throughout each day of exposure to the visual stimuli. Cats spent relatively little of the total observation time (6.10%) looking at the television monitors. Animals exposed to the programmes depicting animate and inanimate forms of movement spent significantly more of their time looking at the monitors than those exposed to the moving images of humans or the blank screen. The amount of attention that the cats directed towards the television monitors decreased significantly across their 3 h of daily presentation, suggesting habituation. Certain components of the cats’ behaviour were influenced by visual stimulation. Animals in the animate movement condition spent significantly less time sleeping, and displayed a non-significant trend to spend more time resting, and in the exercise area of their pens, than those in the other conditions of visual stimulation. Overall, the results from this study suggest that visual stimulation in the form of two-dimensional video-tape sequences, notably that combining elements of prey items and linear movement, may hold some enrichment potential for domestic cats housed in rescue shelters. Such animals, however, may not benefit from this type of enrichment to the same degree as species with more well-developed visual systems, such as primates.     

Motor Activity Improves Temporal Expectancy

Certain brain areas involved in interval timing are also important in motor activity. This raises the possibility that motor activity might influence interval timing. To test this hypothesis, we assessed interval timing in healthy adults following different types of training. The pre- and post-training tasks consisted of a button press in response to the presentation of a rhythmic visual stimulus. Alterations in temporal expectancy were evaluated by measuring response times. Training consisted of responding to the visual presentation of regularly appearing stimuli by either: (1) pointing with a whole-body movement, (2) pointing only with the arm, (3) imagining pointing with a whole-body movement, (4) simply watching the stimulus presentation, (5) pointing with a whole-body movement in response to a target that appeared at irregular intervals (6) reading a newspaper. Participants performing a motor activity in response to the regular target showed significant improvements in judgment times compared to individuals with no associated motor activity. Individuals who only imagined pointing with a whole-body movement also showed significant improvements. No improvements were observed in the group that trained with a motor response to an irregular stimulus, hence eliminating the explanation that the improved temporal expectations of the other motor training groups was purely due to an improved motor capacity to press the response button. All groups performed a secondary task equally well, hence indicating that our results could not simply be attributed to differences in attention between the groups. Our results show that motor activity, even when it does not play a causal or corrective role, can lead to improved interval timing judgments.     

Seeing your error alters my pointing: observing systematic pointing errors induces sensori-motor after-effects

During the procedure of prism adaptation, subjects execute pointing movements to visual targets under a lateral optical displacement: as consequence of the discrepancy between visual and proprioceptive inputs, their visuo-motor activity is characterized by pointing errors. The perception of such final errors triggers error-correction processes that eventually result into sensori-motor compensation, opposite to the prismatic displacement (i.e., after-effects). Here we tested whether the mere observation of erroneous pointing movements, similar to those executed during prism adaptation, is sufficient to produce adaptation-like after-effects. Neurotypical participants observed, from a first-person perspective, the examiner's arm making incorrect pointing movements that systematically overshot visual targets location to the right, thus simulating a rightward optical deviation. Three classical after-effect measures (proprioceptive, visual and visual-proprioceptive shift) were recorded before and after first-person's perspective observation of pointing errors. Results showed that mere visual exposure to an arm that systematically points on the right-side of a target (i.e., without error correction) produces a leftward after-effect, which mostly affects the observer's proprioceptive estimation of her body midline. In addition, being exposed to such a constant visual error induced in the observer the illusion "to feel" the seen movement. These findings indicate that it is possible to elicit sensori-motor after-effects by mere observation of movement errors.     

Kinematics of the Coordination of Pointing during Locomotion

In natural motor behaviour arm movements, such as pointing or reaching, often need to be coordinated with locomotion. The underlying coordination patterns are largely unexplored, and require the integration of both rhythmic and discrete movement primitives. For the systematic and controlled study of such coordination patterns we have developed a paradigm that combines locomotion on a treadmill with time-controlled pointing to targets in the three-dimensional space, exploiting a virtual reality setup. Participants had to walk at a constant velocity on a treadmill. Synchronized with specific foot events, visual target stimuli were presented that appeared at different spatial locations in front of them. Participants were asked to reach these stimuli within a short time interval after a “go” signal. We analysed the variability patterns of the most relevant joint angles, as well as the time coupling between the time of pointing and different critical timing events in the foot movements. In addition, we applied a new technique for the extraction of movement primitives from kinematic data based on anechoic demixing. We found a modification of the walking pattern as consequence of the arm movement, as well as a modulation of the duration of the reaching movement in dependence of specific foot events. The extraction of kinematic movement primitives from the joint angle trajectories exploiting the new algorithm revealed the existence of two distinct main components accounting, respectively, for the rhythmic and discrete components of the coordinated movement pattern. Summarizing, our study shows a reciprocal pattern of influences between the coordination patterns of reaching and walking. This pattern might be explained by the dynamic interactions between central pattern generators that initiate rhythmic and discrete movements of the lower and upper limbs, and biomechanical factors such as the dynamic gait stability.     

Coordination of eye and head movements in cats

Horizontal displacements of gaze in cats with unrestrained head were studied using the magnetic search coil method. Three types of eye-head coordination were found when cats oriented gaze towards visual targets. Maximal velocities of gaze, head and eye movements in orbits depend linearily on amplitudes of their displacements in the range of up to 20 degrees. Gaze velocity reached its top level in about 0.3 of complete time of movement execution. Data support the idea of saccadic-vestibular summation during coordinated eye-head movements in cats.     

Distinct motor plans form and retrieve distinct motor memories for physically identical movements

We can adapt movements to a novel dynamic environment (e.g., tool use, microgravity, and perturbation) by acquiring an internal model of the dynamics. Although multiple environments can be learned simultaneously if each environment is experienced with different limb movement kinematics, it is controversial as to whether multiple internal models for a particular movement can be learned and flexibly retrieved according to behavioral contexts. Here, we address this issue by using a novel visuomotor task. While participants reached to each of two targets located at a clockwise or counter-clockwise position, a gradually increasing visual rotation was applied in the clockwise or counter-clockwise direction, respectively, to the on-screen cursor representing the unseen hand position. This procedure implicitly led participants to perform physically identical pointing movements irrespective of their intentions (i.e., movement plans) to move their hand toward two distinct visual targets. Surprisingly, if each identical movement was executed according to a distinct movement plan, participants could readily adapt these movements to two opposing force fields simultaneously. The results demonstrate that multiple motor memories can be learned and flexibly retrieved, even for physically identical movements, according to distinct motor plans in a visual space.     

The Effects of Ageing and Visual Field Loss on Pointing to Visual Targets

Purpose

To investigate the effect of ageing on visuomotor function and subsequently evaluate the effect of visual field loss on such function in older adults.

Methods

Two experiments were performed: 1) to determine the effect of ageing on visual localisation and subsequent pointing precision, and 2) to determine the effect of visual field loss on these outcome measures. For Experiment 1, we measured visual localisation and pointing precision radially at visual eccentricities of 5, 10 and 15° in 25 older (60–72 years) and 25 younger (20–31 years) adults. In the pointing task, participants were asked to point to a target on a touchscreen at a natural pace that prioritised accuracy of the touch. In Experiment 2, a subset of these tasks were performed at 15° eccentricity under both monocular and binocular conditions, by 8 glaucoma (55–76 years) and 10 approximately age-matched controls (61–72 years).

Results

Visual localisation and pointing precision was unaffected by ageing (p>0.05) and visual field loss (p>0.05), although movement time was increased in glaucoma (p = 0.01).

Conclusion

Visual localisation and pointing precision to high contrast stimuli within the central 15° of vision are unaffected by ageing. Even in the presence of significant visual field loss, older adults with glaucoma are able perform such tasks with reasonable precision provided the target can be perceived and movement time is not restricted.     

双眼和单眼视觉剥夺猫外膝体细胞的图形适应

为测定丘脑外膝体细胞的图形适应是否依赖于早期视觉经验,在细胞外记录了双眼和单眼缝合的猫外膝体中断细胞对手工时间运动光栅刺激的反应。在双眼剥夺猫,占６８％的记录到的细胞在３０ｓ内反应下降到稳定值,其平均反应值下降３３％,适应程度较正常猫显著。在单眼剥夺猫,记录到的剥夺眼驱动的和非剥夺眼驱动的细胞中,分别有占５３％和４４％的细胞显示图形适应,两者差别不大。研究表明,早期视剥夺能增强或保持图形适应,提示     

Impairments and recovery of the spatial and temporal components of a visuomotor pointing movement after unilateral destruction of the dentate nucleus in the baboon.

In baboons trained to perform visuomotor pointing movements, unilateral electrolytic lesions are performed in the dentate nucleus. The consequences of these lesions on the following movement parameters are then studied:--temporal parameters: reaction time and movement time;--spatial parameters: pointing area and directional errors. From the observations taken 3 months after the dentate nucleus exclusion, a distinction can be made between parameters showing recovery phenomena (reaction time and pointing area) and components definitively affected (movement time and directional error).     

Bidirectional regulation of mitochondrial gene expression during developmental neuroplasticity of visual cortex

The first several months of life are a critical period for neuronal plasticity in the visual cortex, during which anatomical and physiological development depends upon visual experience. Rearing in darkness slows the time course of this critical period, such that at 5 weeks normal cats are more plastic than dark-reared cats, while at 20 weeks dark-reared cats are more plastic. This study reports the identification of a subset of mitochondrial genes that are regulated in this manner. Opponent patterns of bidirectional expression were found: several genes (ATPase 6, cytochrome b, NADH dehydrogenase subunits 4 and 2) showed elevation in normal cats at 5 weeks and in dark-reared cats at 20 weeks ("plasticity" genes); others (NADH dehydrogenase subunits 3 and 5) showed the opposite ("anti-plasticity" genes). These findings add a new dimension to the growing evidence that changes in mitochondrial gene expression are involved in the neuroplastic response.     

视皮层反馈对猫外膝体神经元方位调制特性的影响

以扫描正弦光栅作为刺激,用冰冻法毁损皮层17、18、19区和外侧上雪氏回(LS区)来阻断皮层对外膝体的反馈投射,记录并描绘了猫外膝体597个细胞的方位调制特性.去视皮层猫外膝体神经元的平均方位选择性强度(Bias)为0.154,与正常猫(0.155)几乎相同,其最优方位偏向于水平方位.与正常猫外膝体不同的是,去视皮层猫外膝体失去了最优方位的切向分布规律,用GABA或KCl压抑皮层活动得到了相近的实验结果.结果说明正常外膝体的最优方位切向分布规律来自皮层反馈投射.     

Program and feedback in the systems organization of a motor act

After simultaneous visual dereceptation, aimed jumps in cats, reinforced by electric shocks, are restored, while those with food reward are irreversibly lost. Yet, after a two-stage dereceptation, the aimed jumps reappeared even in case when they had food reinforcement. The adequacy of their performance depended on the stability of the distance between the starting sites. The possibility of local cortical control of motor units was demonstrated which is considered as a component of the general mechanism of urgent identification of the motor system state, via somatic afferent pathways. The ablation of their higher link (the medial lemniscus) at the level where it enters the thalamus, disturbs the biomechanics of the aimed jump, increasing the number of multisensory responses of single sensorimotor cortical units. It is suggested that the motivation and the program of the movement corrected by feedback, provide for its adaptive character.     

Simultaneous Postural Adjustments (SPA) scrutinized using the Lissajous method

The goal of this research was to study the postural adjustments that occur during the course of a voluntary movement (Simultaneous Postural Adjustments: SPA). A pointing task performed at maximal velocity was considered and upper limb kinematics and body kinetics were recorded. A 2-DOF model was elaborated that distinguishes between the body segments that are mobilized in order to perform the pointing movement. These segments are the right upper limb (termed the “focal” component) and the rest of the body (termed the “postural” component). This model allowed for the calculation of both sub-systems? kinetics and a comparison of the resultant reaction (RoSh) with the corresponding action (AoSh) at the shoulder level. The analysis was based on the ellipsoidal shape of their relationship. The ellipse computation (“Lissajous ellipse”) allowed the time lag to be estimated. The results showed that the kinetics of the postural component preceded that of the focal ones and that the time lag during the SPA was not statistically different from the APA duration (dAPA). In addition, the kinetics of the postural component were found to be opposed to the perturbation induced by the pointing movement, but only during part of the SPA time interval. It was concluded that the postural component plays a dual role during the movement, which consists of postural stabilization and propulsive action, with one prevailing over the other depending on the time-instant of movement evolution. This new evidence in healthy subjects is helpful to further specify differences associated with motor impairments.     

Effects of head position on errors in 3-D pointing to remembered locations

The accuracy of pointing movements performed under different head positions to remembered target locations in 3-D space was studied in healthy persons. The subjects fixated a visual target, then closed their eyes and after 1.0 sec performed the targeted movement with their right arm. The target (a point light source) was presented in random order by a programmable robot arm at one of five space locations. The accuracy of pointing movements was examined in a spherical coordinate system centered in respect with the shoulder of the responding arm. The pointing movements were most accurate under natural eye-head coordination. With the head fixed in the straight-ahead position, both the 3-D absolute error and its standard deviation increased significantly. At the same time, individual components of spatial error (directional and radial) did not change significantly. With the head turned to the rightmost or leftmost position, the pointing accuracy was disturbed within larger limits than under head-fixed condition. The main contributors to the 3-D absolute error were the changes in the azimuth error. The latter depended on the direction of the head-turn: the rightmost turn either increased leftward or decreased rightward shift, and conversely, the left turn increased rightward shift or decreased leftward shift of the target-directed movements.It is suggested that the increased inaccuracy of pointing under head-fixed condition reflected the impairment of the eye-head coordination underlying gaze orientation, and increased inaccuracy under the head-turned condition may be explained by changes in the internal representation of the head and target position in space.Neirofiziologiya/Neurophysiology, Vol. 26, No. 2, pp. 122–131, March–April, 1994.     

Optimal response of eye and hand motor systems in pointing at a visual target

The closed loop situation of hand pointing at a target has been experimentally divided into its static and dynamic components. When the subjects see their hand at first (closed loop) until the start of the hand movement cuts off the vision of the hand (open loop), the pointing is significantly more accurate than when it is performed without any vision of the hand before and throughout the movement (fully open loop). This suggests that initial cues as regards hand and target position, improve the motor program by a better identification of initial and final states. As poor as it is, the extra retinal signal (encoding of eye position) improves performance when the foveation is done under closed loop; it allows a better redefinition of target position, and thus modulates the hand motor program through a direct central pathway, which is quicker than the processing of the visual feedback of the hand movement error.     

When Kinesthesia Becomes Visual: A Theoretical Justification for Executing Motor Tasks in Visual Space

Several experimental studies in the literature have shown that even when performing purely kinesthetic tasks, such as reaching for a kinesthetically felt target with a hidden hand, the brain reconstructs a visual representation of the movement. In our previous studies, however, we did not observe any role of a visual representation of the movement in a purely kinesthetic task. This apparent contradiction could be related to a fundamental difference between the studied tasks. In our study subjects used the same hand to both feel the target and to perform the movement, whereas in most other studies, pointing to a kinesthetic target consisted of pointing with one hand to the finger of the other, or to some other body part. We hypothesize, therefore, that it is the necessity of performing inter-limb transformations that induces a visual representation of purely kinesthetic tasks. To test this hypothesis we asked subjects to perform the same purely kinesthetic task in two conditions: INTRA and INTER. In the former they used the right hand to both perceive the target and to reproduce its orientation. In the latter, subjects perceived the target with the left hand and responded with the right. To quantify the use of a visual representation of the movement we measured deviations induced by an imperceptible conflict that was generated between visual and kinesthetic reference frames. Our hypothesis was confirmed by the observed deviations of responses due to the conflict in the INTER, but not in the INTRA, condition. To reconcile these observations with recent theories of sensori-motor integration based on maximum likelihood estimation, we propose here a new model formulation that explicitly considers the effects of covariance between sensory signals that are directly available and internal representations that are ‘reconstructed’ from those inputs through sensori-motor transformations.     

Optimal response of eye and hand motor systems in pointing at a visual target

In a task requiring an optimal hand pointing (with regards to both time and accuracy) at a peripheral target, there is first a saccade of the eye within 250 ms, followed 100 ms later by the hand movement. However the latency of the hand movement is poorly correlated with that of the eye movement. When the peripheral target is cut off at the onset of the saccade, there is no correlation between the error of the gaze position and the error of the hand pointing. This suggests an early parallel processing of the two motor outputs. The duration of hand movement does not change significantly when subjects either see or not see their hand (closed or open loop). In the open loop situation, the undershoot of the hand pointing increases with target eccentricity, whatever the subjects are allowed or not to do a saccade toward the target. It suggests that the encoding of eye position by itself is a poor index for an accurately guided movement of the hand.     

Role of the neocortical and subcortical commissures in the interhemispheric transfer of visual information to the hippocampus

The light flash evoked potentials were recorded in the hippocamp of cats with transected left optic tract and cerebral commissures. The data obtained show a significant reduction in the response amplitude (by 1.5-2 times) in both hemispheres after unilateral transection of the optic tract. The minimal response amplitude (10-15 times less than normal) was recorded in the left hippocamp of cats with additional transection of the commissures of the endbrain, mesencephalon and diencephalon. In contrast, the latent period of the first and second components of the evoked potential was similar to that in the control group animals. It is suggested that the neocortical commissural visual inputs play the most important role in interhemispheric transmission of visual information to the hippocamp.     

Visual-vestibular convergence in the vestibular nuclei of the cat

Responses from neurons of the vestibular nuclei were recorded in N₂O-anaesthetized cats. Most neurons in the rostral parts of the nuclei responded to bimodal visual-vestibular stimulation, following a trapezoidal velocity profile. Both combinations of the two stimuli were tested: rotation of the animal with stationary visual field and rotation with overtaking visual field, i.e. the visual pattern running in the same direction as the turntable with twice the velocity. Some correlation of physiological data with results in corresponding psychophysical experiments were found. As a possible biological function of visual-vestibular convergence a phylogenetic solution for discrimination of body and outer world movement is discussed.