Egocentric and allocentric localization during induced motion

This research examined motor measures of the apparent egocentric location and perceptual measures of the apparent allocentric location of a target that was being seen to undergo induced motion (IM). In Experiments 1 and 3, subjects fixated a stationary dot (IM target) while a rectangular surround stimulus (inducing stimulus) oscillated horizontally. The inducing stimulus motion caused the IM target to appear to move in the opposite direction. In Experiment 1, two dots (flashed targets) were flashed above and below the IM target when the surround had reached its leftmost or rightmost displacement from the subject’s midline. Subjects pointed open-loop at either the apparent egocentric location of the IM target or at the bottom of the two flashed targets. On separate trials, subjects made judgments of the Vernier alignment of the IM target with the flashed targets at the endpoints of the surround’s oscillation. The pointing responses were displaced in the direction of the previously seen IM for the IM target and to a lesser degree for the bottom flashed target. However, the allocentric Vernier judgments demonstrated no perceptual displacement of the IM target relative to the flashed targets. Thus, IM results in a dissociation of egocentric location measures from allocentric location measures. In Experiment 2, pointing and Vernier measures were obtained with stationary horizontally displaced surrounds and there was no dissociation of egocentric location measures from allocentric location measures. These results indicate that the Roelofs effect did not produce the pattern of results in Experiment 1. In Experiment 3, pointing and Vernier measures were obtained when the surround was at the midpoint of an oscillation. In this case, egocentric pointing responses were displaced in the direction of surround motion (opposite IM) for the IM target and to a greater degree for the bottom flashed target. However, there was no apparent displacement of the IM target relative to the flashed targets in the allocentric Vernier judgments. Therefore, in Experiment 3 egocentric location measures were again dissociated from allocentric location measures. The results of this experiment also demonstrate that IM does not generate an allocentric displacement illusion analogous to the “flash-lag” effect.

Egocentric and allocentric reference frames for catching a falling object

When programming movement, one must account for gravitational acceleration. This is particularly important when catching a falling object because the task requires a precise estimate of time-to-contact. Knowledge of gravity’s effects is intimately linked to our definition of ‘up’ and ‘down’. Both directions can be described in an allocentric reference frame, based on visual and/or gravitational cues, or in an egocentric reference frame in which the body axis is taken as vertical. To test which frame humans use to predict gravity’s effect, we asked participants to intercept virtual balls approaching from above or below with artificially controlled acceleration that could be congruent or not with gravity. To dissociate between these frames, subjects were seated upright (trunk parallel to gravity) or lying down (body axis orthogonal to the gravitational axis). We report data in line with the use of an allocentric reference frame and discuss its relevance depending on available gravity-related cues.     

Context-dependent reorganization of spatial and movement representations by simultaneously recorded hippocampal and striatal neurons during performance of allocentric and egocentric tasks

Hippocampal and striatal place- and movement-correlated cell firing was recorded as rats performed place or response tasks in a familiar environment, and then after cue manipulation. In a familiar environment, place field properties did not differ across brain structures or task conditions. Movement correlates were stronger during place task performance only in hippocampal neurons. After cue manipulations, place- and movement-sensitive hippocampal and striatal neurons changed their correlate strength, regardless of behavioral strategy. Thus, for both structures, place-correlated cells may encode spatial context information, whereas movement-correlated cells may represent both egocentric movement and learned behavioral responses. The striking overall similarity between hippocampal and striatal neural responses to context manipulation (regardless of strategy) suggests that these structures operate continuously, and in parallel, during multiple forms of learning.     

Pointing movements are affected by size-contrast illusions

 The influence that the perceived size of visual targets has on the characteristics of pointing movements was investigated in the present study. A size-contrast illusion, known as the Ebbinghaus or Tichener circles, was employed. In this illusion, a target circle surrounded by several smaller circles is perceived to be larger than a target circle of the same physical size surrounded by several larger circles. Movement times of open-loop pointing responses directed to the perceptually smaller target circle were significantly longer than the movement times of pointing responses directed to the perceptually larger target circle. The extent of this difference was similar to that observed when pointing responses were directed at physically different-sized target circles that were not surrounded by other circles. In addition, when the perceptually smaller circle was enlarged so that it appeared to be the same size as the perceptually larger circle, the movement times became equivalent. This evidence supports the contention that the relative rather than the absolute size of the target has a major impact on the control and execution of pointing movements. Such a conclusion contradicts those made previously concerning grasping movements made under similar conditions and implies that pointing responses are more directly influenced by visual perceptual processing than grasping responses. Received: 3 September 1998 / Accepted: 15 December 1998     

Patterns of canal and otolith afferent input convergence in frog second-order vestibular neurons

Second-order vestibular neurons (2 degrees VN) were identified in the isolated frog brain by the presence of monosynaptic excitatory postsynaptic potentials (EPSPs) after separate electrical stimulation of individual vestibular nerve branches. Combinations of one macular and the three semicircular canal nerve branches or combinations of two macular nerve branches were stimulated separately in different sets of experiments. Monosynaptic EPSPs evoked from the utricle or from the lagena converged with monosynaptic EPSPs from one of the three semicircular canal organs in ~30% of 2 degrees VN. Utricular afferent signals converged predominantly with horizontal canal afferent signals (74%), and lagenar afferent signals converged with anterior vertical (63%) or posterior vertical (37%) but not with horizontal canal afferent signals. This convergence pattern correlates with the coactivation of particular combinations of canal and otolith organs during natural head movements. A convergence of afferent saccular and canal signals was restricted to very few 2 degrees VN (3%). In contrast to the considerable number of 2 degrees VN that received an afferent input from the utricle or the lagena as well as from one of the three canal nerves (~30%), smaller numbers of 2 degrees VN (14% of each type of 2 degrees otolith or 2 degrees canal neuron) received an afferent input from only one particular otolith organ or from only one particular semicircular canal organ. Even fewer 2 degrees VN received an afferent input from more than one semicircular canal or from more than one otolith nerve (~7% each). Among 2 degrees VN with afferent inputs from more than one otolith nerve, an afferent saccular nerve input was particularly rare (4-5%). The restricted convergence of afferent saccular inputs with other afferent otolith or canal inputs as well as the termination pattern of saccular afferent fibers are compatible with a substrate vibration sensitivity of this otolith organ in frog. The ascending and/or descending projections of identified 2 degrees VN were determined by the presence of antidromic spikes. 2 degrees VN mediating afferent utricular and/or semicircular canal nerve signals had ascending and/or descending axons. 2 degrees VN mediating afferent lagenar or saccular nerve signals had descending but no ascending axons. The latter result is consistent with the absence of short-latency macular signals on extraocular motoneurons during vertical linear acceleration. Comparison of data from frog and cat demonstrated the presence of a similar organization pattern of maculo- and canal-ocular reflexes in both species.     

Abnormal knee kinematics caused by mechanical alignment in symmetric bicruciate-retaining total knee arthroplasty are alleviated by kinematic alignment

BackgroundBicruciate-retaining total knee arthroplasty (BCR-TKA) was developed to maintain anterior cruciate ligament function and thus reproduce natural knee kinematics postoperatively. Traditional surgical techniques, however, may cause several complications secondary to kinematic conflict and ligament overtension. The objective of this study was to use a computer simulation of symmetric BCR-TKA to evaluate the effects of alternative surgical techniques on knee kinematics and ligaments.MethodsA musculoskeletal computer model of a healthy knee was constructed and was used to simulate a BCR model with mechanical alignment (MA). Five adjusted models were investigated, characterized, respectively, by kinematic alignment (KA), two degrees increased tibial slope, two-millimeter distal setting of the tibial component, and an undersized femoral component with either MA or KA.ResultsAll models exhibited a normal femoral position against the tibia at knee extension, with no anterior paradoxical motion during mid-flexion. The healthy knee model showed medial pivot motion and rollback. In contrast, the BCR MA model demonstrated abnormal bi-condylar rollback with excessive tensions of the lateral collateral ligament and posterior cruciate ligament during knee flexion, whereas the undersized femoral model with MA partly reduced both tensions. The BCR KA model retained relatively physiological kinematics and suppressed excessive ligament tensions. However, no adjusted model completely reproduced healthy knee conditions.ConclusionsThe BCR MA model showed abnormal biomechanics due to kinematic conflict between the retained ligaments and the replaced joint surface. Surgeons using symmetric BCR-TKA should consider using the KA method to achieve sufficient ligament laxity throughout knee flexion.     

Event-related beta oscillations are affected by emotional eliciting stimuli

According to previous results, negative emotional facial expressions elicit oscillatory beta responses. The present study analyzes event-related beta oscillations upon presentation of International Affective Picture System (IAPS) and aims to show whether behavior of beta in response to negative IAPS pictures also have similar dynamics. IAPS pictures (unpleasant, pleasant, and neutral) were presented as a block and random passive viewing to 14 healthy subjects (8 male). Only with pictures with similar luminance level were selected as stimuli. Event-Related Potentials (ERPs) were recorded from 30 different scalp locations, and adaptive digital filtering was used for analysis in different frequency windows. The maximum peak-to-peak amplitudes were measured for each subject's averaged beta responses (15–30 Hz) in the 0 and 300 ms time window. Beta responses were significantly higher for unpleasant pictures than for pleasant and neutral pictures (average 50%). Beta responses were significantly higher for unpleasant than for pleasant pictures over frontal, central and parietal electrode sides (p < 0.05). Furthermore, beta responses were significantly higher for unpleasant than for neutral pictures over parietal and occipital electrodes (p < 0.04). In addition, the pleasant pictures elicited higher beta responses than neutral pictures over occipital electrode sites (p < 0.04). The results of the present study indicate that negative emotions are related to increased beta responses in humans, independent of stimulus types (facial expression or IAPS pictures). Accordingly, beta responses to negative emotions are possibly a common phenomenon. The standardization of luminance in pictures may reduce divergences between results from different laboratories.     

Growth and activity but not maturation are affected by perinatal diet

Growth, maturation and activity in Sprague-Dawley rat offspring were studied as a function of two diets which were offered both pre- and postnatally. Day 1 gravid rats were placed ad lib on either Purina chow or Ensure, a total liquid diet. Half of each group was switched to the other diet on day 21 of gestation and maintained on it through weaning. Offspring remained on the same diet until sacrificed on postnatal day 60. Seven developmental measures were assessed daily until all of the animals reached criterion. The type of diet significantly affected maternal weight gain during the second third of gestation, and neonatal weight gain as measured on days 7, 14, 21, 28 and 45. Females were affected more than were male littermates. Males were significantly heavier than female littermates at all postnatal weighings. Diet had little or no effect on the developmental measures. Male/female differences were found for voluntary activity in the wheel which was measured on day 45. The use of liquid diets in behavioral teratology studies and the wisdom of using pellet diets as a control are discussed. The possibility of substituting careful measures of growth as an alternative to developmental testing is discussed.     

Serum theophylline concentrations are not affected by coadministration of doxycycline

Doxycycline (D) is often administered during respiratory infections to asthmatic patients, many of them treated by theophylline (T) as well. We therefore investigated a possible interaction between D and T. Steady-state basal T levels were measured on two successive days before and after three and four days of D administration in ten stable asthmatic patients. Mean T levels before D were 9.9 +/- 3.1 micrograms/mL and after D 10.1 +/- 2.9 micrograms/mL, which are not significantly different. But T levels in four patients increased and in two patients, T levels decreased. We conclude that in some patients, T concentrations may be affected by D. This may require determination of T blood levels and T dose adjustment in some patients treated by T and D.     

Simulation of the ligament forces affected by prosthetic alignment in a trans-tibial amputee case study

The aims of this study were to predict and explain the patterns of ligament forces in the stump of a left trans-tibial amputee during walking, and to study the effects of the prosthetic alignment. Musculoskeletal modeling and computer simulation were combined to calculate ligament forces. The prosthesis was aligned to be in optimal position for the subject and then changed by ±6° in the sagittal plane. The results showed most ligaments bearing the maximum tension forces around both heel-strike and toe-off. The PT force was the biggest in all of the ligaments which were studied. The load patterns of ACL and PCL were opposite in the gait cycle, but the load patterns of MCL and LCL appeared similar. The above results showed that the ligament forces increased at the incorrect alignment, because the incorrect alignment could break the relative translation of the femur and tibia, and that would generate the extra ligament strains. As a result, the ligament forces increased, and the long-duration fatigue occurred more easily. This finding suggests that the proper prosthetic alignment is very important for the normal activities of the stump ligaments.     

Theta oscillations are affected by amnestic mild cognitive impairment and cognitive load

Amnestic mild cognitive impairment (aMCI) is classified primarily via substantial episodic memory deficits in the absence of a dementia diagnosis. To investigate the potential neurophysiological correlates of such deficits we compared QEEG power between 12 participants with aMCI and 12 healthy matched controls. EEG was acquired during performance of a modified Sternberg word recognition task with low and high memory load conditions. While recognition accuracy of aMCI participants was lower than that of controls, this difference was not significant. Nevertheless the aMCI group demonstrated significantly lower theta power at a number of electrode sites and significant correlations were observed between power at these sites and neuropsychological assessment scores. Furthermore in the aMCI sample only, theta power was significantly lower under high versus low memory load. Given current interpretations of the neural generator(s), as well as the role(s), of theta oscillations in cognitive processes, the present data indicate that aMCI may be associated with disruptions in the operation of neurocognitive networks (e.g., MTL-neocortical), particularly under high cognitive load.     

Smoking-induced changes in endothelium and platelets are not affected by hydroxyethylrutosides.

A random-order, double-blind crossover study was carried out to compare the effects of placebo and hydroxyethylrutosides on the endothelial cell count, platelet aggregate ratio and plasma concentrations of beta-thromboglobulin and platelet factor 4 in venous blood before and after smoking. Each of 24 male habitual smokers and 22 male non-smokers smoked two cigarettes during each of two 20 min periods separated by 1 week. The subjects were asked to take 600 mg of o-(beta-hydroxyethyl)-rutosides (Venoruton) or a placebo four times before each experimental smoking period and to abstain from smoking for 12 h before each period. Blood was obtained just before and after experimental smoking. The mean endothelial cell count and beta-thromboglobulin concentration increased and platelet aggregate ratio decreased to a statistically significant extent after taking placebo or rutosides while the platelet factor 4 concentration did not change significantly on either occasion. Plasma nicotine concentrations were not significantly correlated with the other variables after smoking. Neither the mean presmoking values nor smoking-induced changes in any variable were significantly affected by rutosides. The data suggest that smoking caused acute endothelial cell desquamation and enhanced platelet function which were not prevented by rutosides.     

K+ channels in PC12 cells are affected by propofol

The effect on K⁺ currents (I _K) of the general anaesthetic propofol (PR) (2,6-diisopropylphenol) was tested in undifferentiated clonal pheochromocytoma (PC12) cells using the patch-clamp technique in whole-cell and single-channel configurations. PR decreased macroscopic I _K amplitudes in a concentration-dependent way from 50 M to 1 mM. The blocking effect was unchanged by repetitive depolarizing pulses and it was independent of the holding potential. Whereas activation of I _K in control conditions was fitted by sigmoidal plus exponential time courses, only the sigmoidal time course gave an adequate fit with PR in the bath. The above effects were reversible. PR concentrations below 140 M decreased single-channel activity for K⁺ channels with unitary conductance of 22 pS, in the voltage range between –40 and 60 mV from a holding potential of –50 mV. In contrast, the anaesthetic had nearly no effect on the opening probability of a channel with conductance of 10 pS. The unitary current amplitudes were unaffected in both channel types. These results suggest that PR action on I _K may depend on the different blocking mechanisms of the K⁺ channels.     

Saccade initiation and accuracy in gaze shifts are affected by visual stimulus significance

The effect of visual stimulus significance on saccade latency and accuracy in gaze shifts was investigated. Stimulus significance refers to the temporal proximity of an imperative stimulus. It was hypothesized that stimulus significance serves as a cue that influences the observer's expectancy for a forthcoming event. Twenty-one undergraduate students participated in two experiments involving monitoring of visual events. Stimuli were a sequence of 1,000 single-digit integers presented one at a time at 9 degrees of visual angle to the left or right of a fixation point in random order. The subject was required to make a manual response after the presentation of a sequence of two odd integers. The probability of the subsequent integer being odd, a "target," after the presentation of an odd integer was 0.75. The integer after a target was always an even integer. When stimulus location was unpredictable (Experiment 1), latency of visually guided saccades to the target was shorter (p < .01) than to the nontarget stimuli. Under the condition of predictable stimulus location (Experiment 2), anticipatory saccades to the target occurred earlier (p < .01), more frequently (p < .01), and more accurately (p < .05). Our results suggest that both timing and accuracy of gaze shift are affected by the observer's expectation of future events.     

The preoptic-suprachiasmatic nuclei though morphologically heterogeneous are equally affected by streptozotocin diabetes

Summary Pituitary and gonadal disorders consistent with abnormal LHRH and LH secretion occur in streptozotocin-diabetic rats. A key role in the synthesis and regulation of LHRH and in the phasic LH release is played by the preoptic-suprachiasmatic region which is mainly formed by the medial preoptic area, the sexually dimorphic nucleus of the medial preoptic area, and the suprachiasmatic nucleus. Therefore we have studied this region by morphology and morphometry in normal and streptozotocindiabetic rats. In normal animals, the neurons of the above mentioned nuclei were morphologically and morphometrically dissimilar. Independent of their localization, reduced cytoplasmic and nuclear areas were observed in the neurons of diabetic animals. These lesions are consistent with hypotrophied neurons. Consequently, diabetes may impair both synthesis and regulation of LHRH and may therefore account for pituitary disorders, testicular atrophy, and lacking preovulatory LH peaks. The structural differences of the neurons of the three nuclei in normal animals underline their different physiological role. Yet, the similarity of the changes found in all three nuclei suggests a generalized hypofunction of the whole preoptic-suprachiasmatic region under diabetic condition.This work was supported by the Schweizer Nationalfonds grant no. 3.120-81 to G.L.R.     

Movement kinematics in prehension are affected by grasping objects of different mass

Previous research has identified that prehension is composed of a reach and a grasp component and that the position and size of the object can independently affect each. However, no effects on prior to contact prehension kinematics have been reported for manipulations in object mass. We felt that this 'lack of a finding' was surprising, as a more accurate grip position on heavier objects would prevent slippage and rotation when lifting the object. Therefore, we hypothesized that increased object mass would effect the grasp component movement kinematics prior to contact in preparation for a stable final grip placement on the object. We report two experiments in which participants reached, grasped and lifted objects of various size and mass, and their movement kinematics were recorded using a motion tracking system. The results showed that the mass of the object significantly influenced prior-to-contact grasp kinematics. Both studies showed that the heavy compared to light objects caused increased peak grasp aperture, a final finger and thumb placement on the object that more closely passed through the object centre of mass, increased lift delay and reduced peak lift velocity. The data are discussed in terms of how object mass influences the reach, grasp and lift components of prehensile movement.     

Anxiety-related behaviors in the elevated zero-maze are affected by genetic factors and retinal degeneration

Anxiety levels were tested in an elevated zero-maze for 8 inbred strains of mice that are used widely in biomedical and behavioral research. Strain differences were observed for activity, latency to enter an open quadrant, open time, and defecation, demonstrating that genetic factors mediate anxiety in this paradigm. Three of the strains have the rdl mutation that causes retinal degeneration and were less anxious in the maze. To discern whether visual acuity is a source of difference on the maze, anxiety levels were tested in a congenic strain in which the rdl allele has been replaced with the wild-type allele. The congenic strain, with normal vision, had higher levels of anxiety. This study provides baseline data for the selection and use of any of these strains in pharmacological challenges in the maze, and provides a starting point for the identification of strains that may have appropriate backgrounds for targeted mutation studies.     

Fast corrective responses are evoked by perturbations approaching the natural variability of posture and movement tasks

A wealth of studies highlight the importance of rapid corrective responses during voluntary motor tasks. These studies used relatively large perturbations to evoke robust muscle activity. Thus it remains unknown whether these corrective responses (latency 20-100 ms) are evoked at perturbation levels approaching the inherent variability of voluntary control. To fill this gap, we examined responses for large to small perturbations applied while participants either performed postural or reaching tasks. To address multijoint corrective responses, we induced various amounts of single-joint elbow motion with scaled amounts of combined elbow and shoulder torques. Indeed, such perturbations are known to elicit a response at the unstretched shoulder muscle, which reflects an internal model of arm intersegmental dynamics. Significant muscle responses were observed during both postural control and reaching, even when perturbation-related joint angle, velocity, and acceleration overlapped in distribution with deviations encountered in unperturbed trials. The response onsets were consistent across the explored range of perturbation loads, with short-latency onset for the muscles spanning the elbow joints (20-40 ms), and long-latency for shoulder muscles (onset > 45 ms). In addition, the evoked activity was strongly modulated by perturbation magnitude. These results suggest that multijoint responses are not specifically engaged to counter motor errors that exceed a certain threshold. Instead, we suggest that these corrective processes operate continuously during voluntary motor control.     

Mammalian CLASPs are required for mitotic spindle organization and kinetochore alignment

CLASP1 and CLASP2 are homologous mammalian proteins, which associate with the ends of growing microtubules, as well as the cell cortex and the kinetochores of mitotic chromosomes. Previous studies have shown that in interphase cells CLASPs can attach microtubule plus ends to the cortex and stabilize them by repeatedly rescuing them from depolymerization. Here we show that CLASP1 and 2 play similar and redundant roles in organizing the mitotic apparatus in HeLa cells. Simultaneous depletion of both CLASPs causes mitotic spindle defects and a significant metaphase delay, which often results in abnormal exit from mitosis. Metaphase delay is associated with decreased kinetochore tension, increased kinetochore oscillations and more rapid microtubule growth. We show that the association of CLASP2 with the kinetochores relies on its C-terminal domain, but is independent of microtubules or association with CLIP-170. We propose that CLASPs exhibit at the kinetochores an activity similar to that at the cortex, providing apparent stabilization of microtubules by locally reducing the amplitude of growth/shortening episodes at the microtubule ends. This local stabilization of microtubules is essential for the formation of normal metaphase spindle, completion of anaphase and cytokinesis.