Combined moxidectin-levamisole treatment against multidrug-resistant gastrointestinal nematodes: A four-year efficacy monitoring in lambs

Nematicide combinations may be a valid strategy to achieve effective nematode control in the presence of drug resistance. The goal of the current trial was to evaluate the pharmaco-parasitological performance of the moxidectin (MOX) and levamisole (LEV) combination after four years of continuous use in lambs naturally parasitized with multi-resistant gastrointestinal nematodes. At the beginning of the trial, 40 lambs were divided into four groups (n = 10), which were untreated (control) or subcutaneously treated with MOX (0.2 mg/kg), LEV (8 mg/kg) or with the combination MOX + LEV (administered separately at 0.2 and 8 mg/kg, respectively). Blood samples were collected at different times post-treatment and LEV and MOX plasma concentrations were measured by HPLC. The clinical efficacy of the continuous use of MOX + LEV combination was assessed with the controlled efficacy test (CET), performed at the beginning and end of the study, and with the faecal egg count reduction (FECR) test, performed over the four-year study period. No significant adverse pharmacokinetic changes were observed either for MOX or LEV after their co-administration to infected lambs. The CET (first year) showed efficacies of 84.3 % (Haemonchus contortus), 100 % (Teladorsagia circumcincta and Trichostrongylus axei), and 97.4 % (T. colubriformis). After the repetitive use of the combined treatment for four years, those efficacies remained high (100 %) and only decreased to 58 % against T. colubriformis. The evaluation of the FECR over the study period showed fluctuations in the performance of the combined administration. The initial FECR (2014) was 99 % (MOX), 85 % (LEV) and 100 % (MOX + LEV). The co-administration of MOX + LEV during the four-year experimental period resulted in a significantly higher anthelmintic effect (87 %) than that of MOX (42 %) or LEV (69 %) given alone. The combined use of MOX + LEV to control resistant gastrointestinal nematodes appears to be a valid strategy under specific management conditions. A high initial therapeutic response to the combination would be a relevant feature for the success of this tool.

Pharmacologic interaction between oxfendazole and triclabendazole: In vitro biotransformation and systemic exposure in sheep

The aim of the current work was to evaluate a potential pharmacokinetic interaction between the flukicide triclabendazole (TCBZ) and the broad-spectrum benzimidazole (BZD) anthelmintic oxfendazole (OFZ) in sheep. To this end, both an in vitro assay in microsomal fractions and an in vivo trial in lambs parasitized with Haemonchus contortus resistant to OFZ and its reduced derivative fenbendazole (FBZ) were carried out. Sheep microsomal fractions were incubated together with OFZ, FBZ, TCBZ, or a combination of either FBZ and TCBZ or OFZ and TCBZ. OFZ production was significantly diminished upon coincubation of FBZ and TCBZ, whereas neither FBZ nor OFZ affected the S-oxidation of TCBZ towards its sulfoxide and sulfone metabolites. For the in vivo trial, lambs were treated with OFZ (Vermox^® oral drench at a single dose of 5 mg/kg PO), TCBZ (Fasinex^® oral drench at a single dose of 12 mg/kg PO) or both compounds at a single dose of 5 (Vermox^®) and 12 mg/kg (Fasinex^®) PO. Blood samples were taken to quantify drug and metabolite concentrations, and pharmacokinetic parameters were calculated by means of non-compartmental analysis. Results showed that the pharmacokinetic parameters of active molecules and metabolites were not significantly altered upon coadministration. The sole exception was the increase in the mean residence time (MRT) of OFZ and FBZ sulfone upon coadministration, with no significant changes in the remaining pharmacokinetic parameters. This research is a further contribution to the study of metabolic drug-drug interactions that may affect anthelmintic efficacies in ruminants.

Pharmacokinetic assessment of the monepantel plus oxfendazole combined administration in dairy cows

Monepantel (MNP) is a novel anthelmintic compound launched into the veterinary pharmaceutical market. MNP is not licenced for use in dairy animals due to the prolonged elimination of its metabolite monepantel sulphone (MNPSO₂ ) into milk. The goal of this study was to evaluate the presence of potential in vivo drug-drug interactions affecting the pattern of milk excretion after the coadministration of the anthelmintics MNP and oxfendazole (OFZ) to lactating dairy cows. The concentrations of both parent drugs and their metabolites were measured in plasma and milk samples by HPLC. MNPSO₂ was the main metabolite recovered from plasma and milk after oral administration of MNP. A high distribution of MNPSO₂ into milk was observed. The milk-to-plasma ratio (M/P ratio) for this metabolite was equal to 6.75. Conversely, the M/P ratio of OFZ was 1.26. Plasma concentration profiles of MNP and MNPSO₂ were not modified in the presence of OFZ. The pattern of MNPSO₂ excretion into milk was also unchanged in animals receiving MNP plus OFZ. The percentage of the total administered dose recovered from milk was 0.09 ± 0.04% (MNP) and 2.79 ± 1.54% (MNPSO₂ ) after the administration of MNP alone and 0.06 ± 0.04% (MNP) and 2.34 ± 1.38% (MNPSO₂ ) after the combined treatment. The presence of MNP did not alter the plasma and milk disposition kinetics of OFZ. The concentrations of the metabolite fenbendazole sulphone tended to be slightly higher in the coadministered group. Although from a pharmacodynamic point of view the coadministration of MNP and OFZ may be a useful tool, the presence of OFZ did not modify the in vivo pharmacokinetic behaviour of MNP and therefore did not result in reduced milk concentrations of MNPSO₂ .

Intestinal drug transport: ex vivo evaluation of the interactions between ABC transporters and anthelmintic molecules

The family of ATP-binding cassette (ABC) transporters is composed of several transmembrane proteins that are involved in the efflux of a large number of drugs including ivermectin, a macrocyclic lactone (ML) endectocide, widely used in human and livestock antiparasitic therapy. The aim of the work reported here was to assess the interaction between three different anthelmintic drugs with substrates of the P-glycoprotein (P-gp) and the breast cancer resistance protein (BCRP). The ability of ivermectin (IVM), moxidectin (MOX) and closantel (CST) to modulate the intestinal transport of both rhodamine 123 (Rho 123), a P-gp substrate, and danofloxacin (DFX), a BCRP substrate, across rat ileum was studied by performing the Ussing chamber technique. Compared to the controls, Rho 123 efflux was significantly reduced by IVM (69%), CST (51%) and the positive control PSC833 (65%), whereas no significant differences were observed in the presence of MOX (30%). In addition, DFX efflux was reduced between 59% and 72% by all the assayed drug molecules, showing a higher potency than that observed in the presence of the specific BCRP inhibitor pantoprazole (PTZ) (52%). An ex vivo intestinal transport approach based on the diffusion chambers technique may offer a complementary tool to study potential drug interactions with efflux transporters such as P-gp and BCRP.

Accumulation of monepantel and its sulphone derivative in tissues of nematode location in sheep: pharmacokinetic support to its excellent nematodicidal activity

The amino-acetonitrile derivatives (AADs) are a new class of anthelmintic molecules active against a wide range of sheep gastrointestinal (GI) nematodes including those that are resistant to other anthelmintic families. The plasma disposition of monepantel (MNP) has been previously characterized in sheep. However, information on drug concentration profiles attained at tissues of parasite location is necessary to fully understand the pharmacological action of this novel compound. The current work aimed to study the relationship between the concentrations of MNP parent drug and its main metabolite monepantel sulphone (MNPSO₂), measured in the bloodstream and in different GI tissues of parasite location in sheep. Twenty two (22) uninfected healthy Romney Marsh lambs received MNP (Zolvix, Novartis Animal Health) orally administered at 2.5 mg/kg. Blood samples were collected from six animals between 0 and 14 days post-treatment to characterize the drug/metabolite plasma disposition kinetics. Additionally, 16 lambs were sacrificed at 8, 24, 48 and 96 h post-administration to assess the drug concentrations in the GI fluid contents and tissues. MNP and MNPSO₂ concentrations were determined by HPLC. MNP parent compound was rapidly oxidized into MNPSO₂. MNP systemic availability was significantly lower than that observed for MNPSO₂. The peak plasma concentrations were 15.1 (MNP) and 61.4 ng/ml (MNPSO₂). The MNPSO₂ to MNP plasma concentration profile ratio (values expressed in AUC) reached a value of 12. Markedly higher concentrations of MNP and MNPSO₂ were measured in both abomasal and duodenal fluid contents, and mucosal tissues compared to those recovered from the bloodstream. A great MNP availability was measured in the abomasal content with concentration values ranging between 2000 and 4000 ng/g during the first 48 h post-treatment. Interestingly, the metabolite MNPSO₂ was also recovered in abomasal content but its concentrations were significantly lower compared to MNP. The parent drug and its sulphone metabolite were detected in the different segments of the sheep intestine. MNPSO₂ concentrations in the different intestine sections sampled were significantly higher compared to those measured in the abomasum. Although MNP is metabolized to MNPSO₂ in the liver, the large concentrations of both anthelmintically active molecules recovered during the first 48 h post-treatment from the abomasum and small intestine may greatly contribute to the well-established pharmacological activity of MNP against GI nematodes.

Are topical oestrogens useful in faecal incontinence? Double-blind randomized trial

BACKGROUND

Histopathological studies have shown the presence of oestrogenic receptors in the anal sphincter, which presumes a role in muscular trophism for circulating oestrogens. This could explain the increase in faecal incontinence (FI) in postmenopausal women.

OBJECTIVE

To evaluate the effect of topical oestrogens (TE) in controlling symptoms of FI in postmenopausal women. Hypothesis The application of TE in postmenopausal women with FI improves continence.

METHOD

We performed a prospective double-blind randomized trial applying TE to the anal mucosa in postmenopausal women with FI.

STUDY PERIOD

2005-2006. The patients were randomized into two groups: I--topical estriol, II--placebo. In both groups, the ointment was applied three times daily for a period of 6 weeks. We compared Wexner's FI score and the FI quality of life scale, before commencing and after 6 weeks of application.

RESULTS

In this period we evaluated 36 patients. Average age: 67 years (48-84). Group I: 18 patients and group II: 18 patients, one patient was excluded. Wexner's FI score in group I was 11 (5-18) and 7 (0-19) with pre- and postapplication respectively (P = 0.002). Wexner's FI score in group II was 12 and 9 with pre- and postapplication respectively (P = 0.013). When we compared the results between both groups, this was not statistically significant (P = 0.521).

CONCLUSION

There is improvement of continence in both groups that had the ointment applied; nonetheless this study could not show that TE improves FI more than a placebo does.

Exploring language barriers to Evidence-based Health Care (EBHC) in post-graduate medical students: a randomised trial

BACKGROUND

Understanding the written English language might be a barrier when teaching Evidence-based Health Care (EBHC) to Spanish-speaking physicians.

AIM

To quantify the magnitude of this potential barrier.

METHOD

Cochrane Review abstracts in English or in Spanish were randomly distributed among first-year residents at the Pontificia Universidad Catolica of Chile. Residents answered investigator-designed questionnaires to measure their comprehension while the time needed to complete the task was recorded.

RESULTS

Groups were similar at baseline. Mean score for those reading in Spanish was 11.9 +/- 2.8 (range 5 to 18) compared to 10.5 +/- 3.8 (range 1 to 17) for those reading in English (p=0.04). Low scores ( pound 9) were twice as frequent for the English group than for the Spanish group (16.7% vs 34.7%; p=0.042). The time to complete the task was also longer for the group reading in English.

CONCLUSION

Language should be taken into account when teaching EBHC to Spanish-speaking physicians.

Perceptuomotor compatibility in pursuit tracking of two-dimensional movements

In a previous article, we reported an investigation of visuomanual pursuit tracking of unpredictable two-dimensional targets. This article extends the study to the tracking of predictable stimuli. In both investigations, the target trajectory was elliptical. The experimental factors we varied were the orientation of the major axis of the ellipses (horizontal or vertical), the period of the movement (9.65 to 1.61 s), and the law of motion (natural vs. transformed). In the natural condition (L), the motion results from the combination of harmonic functions, as would be the case if the target were generated by a human. In the transformed (T) condition, the law of motion departs systematically from this natural model. The main results of the study are as follows: (a) Satisfactory performance is achieved only in the natural condition. Pursuit movements obey the same constraints observed in spontaneous movements. (b) Predictability affects significantly the average delay between target and pursuit. (c) Each component of the pursuit movements depends on both components of the targets. Thus, two-dimensional tracking generalizes significantly the classical one-dimensional condition. (d) The simple model developed previously to describe performance with unpredictable targets can be generalized to cover the present case as well.

Colour, form, and movement are not perceived simultaneously

Behavioural, neuro-anatomical and clinical evidence suggests that different aspects of the visual scene are processed separately, but the extent to which the processing is carried out along segregated and independent parallel pathways is still debated. Moreover, it is also unclear whether these aspects are processed at the same rate, and their neural correlates reach consciousness at the same time. An experiment investigated this issue in the case of three attributes of 2D displays: colour, form, and movement. There were three conditions, one for each possible pairing of these attributes. Stimuli were combinations of two values for each attribute (red/green, circle/square, fixed/moving). In each condition the stimuli changed twice in close temporal succession, each attribute switching asynchronously between the two possible values. The observer's task was to report which change had occurred first. Response probabilities were computed for 13 values of the asynchrony, and transformed into estimates of perception time with the help of a psychophysical model. The results showed that colour and form are processed almost simultaneously. By contrast, movement perception is delayed by about 50 ms. The implications of these findings vis à vis the so-called perceptual binding problem are discussed.

[Determination of opiates in urine: interpretation of comparison between the EIA and FPIA and confirmation of data with GC/MS]

BACKGROUND

The aim of this study was to evaluate some urine samples and to analyse them using two immunochemical screening methods.

METHODS

A more reliable method has been used to obtain a critical analysis of the validity of the first analysis methods used. A total of 147 urine samples were examined using both the FPIA technique (Adx, Abbott) and the EIA technique (Random 120, Bracco); confirmation was obtained using GC/MS.

RESULTS

When the threshold was altered from 200 to 300 ng/ml the EIA technique is more severely affected by changes in reference values compared to FPIA. In different values between two techniques, confirmation with GC/MS was possible only 5 cases.

CONCLUSIONS

The study of data processing with immunochemical tests and after confirmation showed that the results with GC/MS are closer to Adx. The FPIA results are in agreement with the GC/MS technique both at 200 and 300 ng/ml with a percentage of 80.0%. The EIA technique has a different result, at 200 ng/ml it is in agreement for 40.0%, but at 300 ng/ml there is only 20.0%.

Proprioception does not quickly drift during visual occlusion

Several perceptual studies have shown that the ability to estimate the location of the arm degrades quickly during visual occlusion. To account for this effect, it has been suggested that proprioception drifts when not continuously calibrated by vision. In the present study, we re-evaluated this hypothesis by isolating the proprioceptive component of position sense (i.e., the subjects were forced to rely exclusively on proprioception to locate their hand, which was not the case in earlier studies). Three experiments were conducted. In experiment 1, subjects were required to estimate the location of their unseen right hand, at rest, using a visual spot controlled by the left hand through a joystick. Results showed that the mean accuracy was identical whether the localization task was performed immediately after the positioning of the hand or after a 10-s delay. In experiments 2 and 3, subjects were required to point, without vision of their limb, to visual targets. These two experiments relied on the demonstration that biases in the perception of the initial hand location induced systematic variations of the movement characteristics (initial direction, final accuracy, end-point variability). For these motor tasks, the subjects did not pay attention to the initial hand location, which removed the possible occurrence of confounding cognitive strategies. Results indicated that movement characteristics were, on average, not affected when a 15-s or 20-s delay was introduced between the positioning of the arm at the starting point and the presentation of the target. When considered together, our results suggest that proprioception does not quickly drift in the absence of visual information. The potential origin of the discrepancy between our results and earlier studies is discussed.

Internally driven vs. externally cued movement selection: a study on the timing of brain activity

Brain imaging studies in man and single cell recordings in monkey have suggested that medial supplementary motor areas (SMA) and lateral pre-motor areas (PMA) are functionally dissociated concerning their involvement in internally driven and externally cued movements. This dichotomy, however, seems to be relative rather than absolute. Here, we searched for further evidence of relative differences and aimed to determine by what aspect of brain activity (duration, strength, or both) these might be accounted for. Event-related potentials (ERPs) were recorded while healthy, right-handed subjects selected one of three possible right hand digit movements based either on 'internal' choice or 'external' cues. The results obtained from ERP mapping suggest that movement selection evokes the same electrical brain activity patterns in terms of surface potential configurations in the same order and at the same strength independent of the selection mode. These identical configurations, however, differed in their duration. Combined with the results of a distributed source localization procedure, our data are suggestive of longer lasting activity in SMA during the 'internal' and longer lasting activity in PMA during the 'external' condition. Our results confirm previous findings in showing that SMA and PMA are distinctively involved in the two tasks and that this functional dichotomy is relative rather than absolute but indicate that such a dissociation can result from differences in duration rather than pure strength of activation.

Perceptual anticipation in handwriting: the role of implicit motor competence

In two experiments, perceptual anticipation--that is, the observer's ability to predict the course of dynamic visual events--in the case of handwriting traces was investigated. Observers were shown the dynamic display of the middle letter l excerpted from two cursive trigrams (lll or lln) handwritten by one individual. The experimental factor was the distribution of the velocity along the trace, which was controlled by a single parameter, beta. Only for one value of this parameter (beta = 2/3) did the display comply with the two-thirds power law, which describes how tangential velocity depends on curvature in writing movements. The task was to indicate the trigram from which the trace was excerpted--that is, to guess the letter that followed the specific instance of the l that had been displayed. In Experiment 1, the no answer option was available. Experiment 2 adopted a forced-choice response rule. Responses were never reinforced. When beta = 2/3, the rate of correct guesses was high (Experiment 1, P¿correct¿ = .69; Experiment 2, P¿correct¿ = .78). The probability of a correct answer decreased significantly for both smaller and larger values of beta, with wrong answers becoming predominant at the extremes of the range of variation of this parameter. The results are consistent with the hypothesis that perceptual anticipation of human movements involves comparing the perceptual stimulus with an internal dynamic representation of the ongoing event.

Does visual sensitivity improve between 5 and 8 years? A study of automated visual field examination

In 74 normal subjects (62 children aged 5-8 years and 12 adults), we tested the widely-held belief that visual sensitivity improves substantially during childhood. Maturation of the retino-striate pathways is generally invoked to account for age-related changes in visual sensitivity. We evaluated the extent to which attentional factors unduly emphasized the effect of age on the purely physiological mechanisms. After a specially-designed familiarization procedure, sensitivity was fully evaluated at two locations in the superior temporal field using a bracketing technique (Octopus 2000R). False-positive (FP) and false-negative (FN) catch-trials were interspersed with the sequence of stimuli. Analyses demonstrated that: (1) age affected sensitivity; and (2) the general level of attentiveness varied not only with age, but also among subjects in the same age group. We then estimated the extent to which improved visual sensitivity may reflect a concomitant evolution of vigilance. Firstly, controlled variance analyses indicated that factors for evaluating attentiveness (rate of FN responses, slope of the psychometric function at the median, and goodness of fit) were indeed much better predictors than age of the sensitivity measured. Secondly and more significantly, the grouping of subjects into homogeneous subgroups, on the basis of their attentional performance, showed that children as young as 5 years may have a visual sensitivity that is only marginally lower than that of adults.

Automated visual field examination in children aged 5-8 years. Part II: Normative values

We determined normative values for the visual sensitivity threshold in 118 children aged 5-8 years, using automated static perimetry (Octopus 2000R, program 32). In addition, 17 normal adults were tested. The children first underwent a familiarization procedure. One week later, quantitative examination was performed according to a specially designed schedule divided into three phases. For each of the 76 points tested, mean thresholds and standard deviations were calculated as a function of age. In contrast to previous studies, sensitivity difference between adults and children over the central 30 degrees of the visual field emerged only for the youngest age groups (5- and 6-year olds). Both the response rate in false-negative trials, and values of a within-subject threshold variability index, suggested that 5- and 6-year-olds' higher thresholds were inflated by non physiological factors, such as vigilance and cognitive processes. For these ages, the data reported here should therefore be considered as an approximation of the upper level of the thresholds. In contrast, our results for 7- and 8 year-old children provided reliable normative values for light sensitivity across the visual field.

Automated visual field examination in children aged 5-8 years. Part I: Experimental validation of a testing procedure

In 106 children aged 5-8 years, we determined how much training was needed to stabilize the response strategy prior to actual visual field assessment and we evaluated the reliability and acceptable duration of automated static perimetry (Octopus 2000R). A specially designed familiarization procedure was used to train the children to: (1) gaze at the center of the visual field while paying attention to light stimuli projected onto the periphery and (2) press the buzzer only when light stimuli were perceived. The subsequent examination phase consisted of 15 successive identical blocks of 27 trials (12 stimulus trials, 12 false-positive catch-trials, and three false-negative catch-trials), and was stopped before the end if signs of fatigue appeared. Age had a marked influence both on endurance (the number of blocks performed increased significantly) and on response reliability (false-positive responses decreased between 5- and 6-year-olds). The increase in false-negative responses toward the end indicates that examination is no longer reliable, and should be stopped. We concluded that most children as young as five can undergo examination by automated static perimetry. Changes regarding learning, stimulus intensity and testing procedure are suggested in order to adapt the examination to age, level of vigilance and health condition of the children.

Pointing errors reflect biases in the perception of the initial hand position

By comparing the visuomotor performance of 10 adult, normal subjects in three tasks, we investigated whether errors in pointing movements reflect biased estimations of the hand starting position. In a manual pointing task with no visual feedback, subjects aimed at 48 targets spaced regularly around two starting positions. Nine subjects exhibited a similar pattern of systematic errors across targets, i.e., a parallel shift of the end points that accounted, on average, for 49% of the total variability. The direction of the shift depended on the starting location. Systematic errors decreased dramatically in the second condition where subjects were allowed to see their hand before movement onset. The third task was to use a joystick held by the left hand to estimate the location of their (unseen) right hand. The systematic perceptual errors in this condition were found to be highly correlated with the motor errors in the first condition. The results support the following conclusions. 1) Kinesthetic estimation of hand position may be consistently biased. Some of the mechanisms responsible for these biases are always active, irrespective of whether position is estimated overtly (e.g., with a matching paradigm), or covertly as part of the motor planning for aimed movements. 2) Pointing errors reflect to a significant extent the erroneous estimation of initial hand position. This suggests that aimed hand movements are planned vectorially, i.e., in terms of distance and direction, rather than in terms of absolute position in space.

Hemispheric asymmetries and bimanual asynchrony in left- and right-handers

It is known that, when both forearms are rotated rhythmically and symmetrically, the dominant hand leads in time by about 25 ms, irrespective of movement speed. Positron emission tomography was used to test the hypothesis that the asynchrony results from a functional hemispheric asymmetry. We found that in normal, adult right-handers portions of the motor and premotor motor areas are more active in the left than in the right hemisphere. The converse pattern was observed in left-handers. The results suggest that at least some components of the neural processing involved in bimanual coordination are carried out only in the hemisphere contralateral to the dominant hand. In particular, between-hands asynchrony may reflect the time for dispatching pace-setting commands to the contralateral hemisphere.

Frames of reference and control parameters in visuomanual pointing

Three hypotheses concerning the control variables in visuomanual pointing were tested. Participants pointed to a visual target presented briefly in total darkness on the horizontal plane. The starting position of the hand alternated randomly among 4 points arranged as a diamond. Results show that during the experiment, movement drifted from hypometric to hypermetric. Final positions depended on the starting position. Their average pattern reproduced the diamond of the starting points, either in same orientation (hypometric trials), or with a double inversion (hypermetric trials). The distribution of variable errors was elliptical, with the major axis aligned with the direction of the movement. Statistical analysis and Monte Carlo simulations showed that the results are incompatible with the final point control hypothesis (A. Polit & E. Bizzi, 1979). Better, but not fully satisfactory, agreement was found with the view that pointing involves comparing initial and desired postures (J. F. Soechting & M. Flanders, 1989a). The hypothesis that accounted best for the results is that final hand position is coded as a vector represented in an extrinsic frame of reference centered on the hand.

Frames of reference and control parameters in visuomanual pointing

Three hypotheses concerning the control variables in visuomanual pointing were tested. Participants pointed to a visual target presented briefly in total darkness on the horizontal plane. The starting position of the hand alternated randomly among 4 points arranged as a diamond. Results show that during the experiment, movement drifted from hypometric to hypermetric. Final positions depended on the starting position. Their average pattern reproduced the diamond of the starting points, either in same orientation (hypometric trials), or with a double inversion (hypermetric trials). The distribution of variable errors was elliptical, with the major axis aligned with the direction of the movement. Statistical analysis and Monte Carlo simulations showed that the results are incompatible with the final point control hypothesis (A. Polit & E. Bizzi, 1979). Better, but not fully satisfactory, agreement was found with the view that pointing involves comparing initial and desired postures (J. F. Soechting & M. Flanders, 1989a). The hypothesis that accounted best for the results is that final hand position is coded as a vector represented in an extrinsic frame of reference centered on the hand.

Pointing to kinesthetic targets in space

An experiment investigated in human adults the sensorimotor transformation involved in pointing to a spatial target identified previously by kinesthetic cues. In the "locating phase," a computer-controlled mechanical arm guided the left [condition LR (left-right)] or right [condition RR (right-right)] finger of the blindfolded participant to one of 27 target positions. In the subsequent "pointing phase," the participant tried to reach the same position with the right finger. The final finger position and the posture of the arm were measured in both conditions. Constant errors were large but consistent and remarkably similar across conditions, suggesting that, whatever the locating hand, target position is coded in an extrinsic frame of reference (target position hypothesis). The main difference between the same-hand (RR) and different-hand (LR) conditions was a symmetric shift of the pattern of endpoints with respect to the midsagittal plane. This effect was modeled accurately by assuming a systematic bias in the perception of the postural angles of the locating arm. The analysis of the variable errors indicated that target position is represented internally in a spherical coordinate system centered on the shoulder of the pointing arm and that the main source of variability is within the planning stage of the pointing movement. Locating and pointing postures depended systematically on target position. We tested qualitatively the hypothesis that the selection of both postures (inverse kinematic problem) is constrained by a minimum-distance principle. In condition RR, pointing posture depended also on the locating posture, implying the presence of a memory trace of the previous movement. A scheme is suggested to accommodate the results within an extended version of the target position hypothesis.

Perceiving and tracking kinesthetic stimuli: further evidence of motor-perceptual interactions

Two experiments pursued previous studies (P. Viviani & P. Mounoud, 1990; P. Viviani & N. Stucchi, 1989) on motor-perceptual interactions. The right arm of blindfolded participants was moved passively along elliptic trajectories. Kinematics was either coherent or at variance with the relation (two-thirds power law) observed in active movements. In Experiment 1 participants compared the horizontal and vertical extent of the ellipses. Kinematics affected aspect ratio discrimination: The direction along which the movement decelerated was subjectively stretched. In Experiment 2 participants used the left arm to reproduce in real time the movement of the right arm. The trajectories of the left arm presented a stretch similar to the perceptual illusion demonstrated in Experiment 1. Between-arm asynchrony suggests that the motor control system cannot use kinesthetic information that is at variance with the flow of reafferences normally associated with voluntary movements. It is argued that these interactions occur at the level of a central amodal representation of the stimuli.

Perceiving and tracking kinesthetic stimuli: further evidence of motor-perceptual interactions

Two experiments pursued previous studies (P. Viviani & P. Mounoud, 1990; P. Viviani & N. Stucchi, 1989) on motor-perceptual interactions. The right arm of blindfolded participants was moved passively along elliptic trajectories. Kinematics was either coherent or at variance with the relation (two-thirds power law) observed in active movements. In Experiment 1 participants compared the horizontal and vertical extent of the ellipses. Kinematics affected aspect ratio discrimination: The direction along which the movement decelerated was subjectively stretched. In Experiment 2 participants used the left arm to reproduce in real time the movement of the right arm. The trajectories of the left arm presented a stretch similar to the perceptual illusion demonstrated in Experiment 1. Between-arm asynchrony suggests that the motor control system cannot use kinesthetic information that is at variance with the flow of reafferences normally associated with voluntary movements. It is argued that these interactions occur at the level of a central amodal representation of the stimuli.

The relationship between curvature and velocity in two-dimensional smooth pursuit eye movements

Curvature and tangential velocity of voluntary hand movements are constrained by an empirical relation known as the Two-Thirds Power Law. It has been argued that the law reflects the working of central control mechanisms, but it is not known whether these mechanisms are specific to the hand or shared also by other types of movement. Three experiments tested whether the power law applies to the smooth pursuit movements of the eye, which are controlled by distinct neural motor structures and a peculiar set of muscles. The first experiment showed that smooth pursuit of elliptic targets with various curvature-velocity relationships was most accurate when targets were compatible with the Two-Thirds Power Law. Tracking errors in all other cases reflected the fact that, irrespective of target kinematics, eye movements tended to comply with the law. Using only compatible targets, the second experiment demonstrated that kinematics per se cannot account for the pattern of pursuit errors. The third experiment showed that two-dimensional performance cannot be fully predicted on the basis of the performance observed when the horizontal and vertical components of the targets used in the first condition were tracked separately. We conclude that the Two-Thirds Power Law, in its various manifestations, reflects neural mechanisms common to otherwise distinct control modules.

Acetazolamide-responsive episodic ataxia in an Italian family refines gene mapping on chromosome 19p13

Episodic ataxia type 2 is an autosomal dominant disorder with attacks of vertigo and ataxia which respond to acetazolamide treatment. The gene, distinct from the KCNA1 responsible for episodic ataxia type 1, has been mapped on chromosome 19p13 in a 11-12 cM region. A large Italian kindred affected with acetazolamide-responsive episodic ataxia is reported, with onset in adulthood, a strong vestibular component during attacks and a high frequency of cerebellar vermis degeneration. The genetic analysis (i) showed strong linkage between the disease and the 19p13 microsatellite markers in a region which widely overlaps that previously reported and (ii) set a new distal boundary of the gene-containing region. Combining present and previous mapping data, the gene of episodic etaxia type 2 is most probably located in an interval approximately 1.5 Mb between markers D19S221 and D19S226.

Feasibility of automated visual field examination in children between 5 and 8 years of age

AIMS

To investigate how young children develop the ability to undergo a visual field evaluation using regular automated perimetry.

METHODS

The study included 42 normal girls aged 5, 6, 7, and 8 years. Twelve locations in the 15 degrees eccentricity were tested in one eye, using an Octopus 2000R perimeter with a two level strategy. False positive and false negative catch trials were presented. The examination was performed three times in succession. Before the examination procedure, a specially designed programme was conducted for progressive familiarisation.

RESULTS

During the familiarisation procedure, it was found that all of the 5-year-old children, seven of the 6-year-old children, and three of the 7-year-old children were unable to perform immediately, and correctly, the instructions given during the familiarisation phase; these children took from 30 seconds to 3 minutes to comply with the examiner's requests. With the exception of one 5-year-old child, all tested subjects completed the planned procedure. The mean proportion of false negative answers in catch trials was 1.6%. The mean proportion of false positive answers was 12.2%. The quadratic dependency on age suggested by the averages was not significant (F(3,116) = 0.88; p = 0.45). Detection stimulus improved with age, as shown by the fact that probability of perceiving dim stimulus increases significantly (F(3,116) = 12.68; p < 0.0001).

CONCLUSION

Children did remarkably well regarding both the duration of the examination and the reliability of the answers. A preliminary familiarisation phase with a specially designed adaptation programme was found to be mandatory with children aged 7 or under. To our knowledge, this is the first time that such an investigation has been performed.

Minimum-jerk, two-thirds power law, and isochrony: converging approaches to movement planning

Two approaches to the study of movement planning were contrasted. Data on the drawing of complex two-dimensional trajectories were used to test whether the covariations of the kinematic and geometrical parameters of the movement formalized by the two-thirds power law and by the isochrony principle (P. Viviani & R. Schneider, 1991) can be derived from the minimum-jerk model hypothesis (T. Flash & N. Hogan, 1985). The convergence of the 2 approaches was satisfactory insofar as the relation between tangential velocity and curvature is concerned (two-thirds power law). Global isochrony could not be deduced from the optimal control hypothesis. Scaling of velocity within movement subunits can instead be derived from the minimum-jerk hypothesis. The implications vis-à-vis the issue of movement planning are discussed with an emphasis on the representation used by the motor control system for coding the intended trajectories.

[Automated static perimetry in the child: methodologic and practical problems]

PURPOSE

In a pediatric population, the use of computerized static perimetry is known as particularly difficult. The specific difficulties which may occur when testing young subjects are stability of fixation, ability to maintain concentration, resistance throughout the procedure, and reliability of the answers. It seems important to investigate and to develop appropriate strategies for the examination of children aged 8 years and younger according to their ability to undergo visual field evaluation using automated static perimetry.

PATIENTS AND METHODS

Eighty normal children aged 5 to 8 years old were evaluated using an Octopus 2000R perimeter, with a one-level strategy. Adaptation of the procedure were included.

RESULTS

The analysis of answers and false-positive catch-trials showed that children as young as five years old did remarkably well regarding both the duration of the examination and the reliability of answers.

CONCLUSIONS

Automated static perimetry examination can provide reliable results in children as young as five years old once a familiarization procedure has been conducted and if the duration of examination does not exceed the child's capacity to remain task focused.

Minimum-jerk, two-thirds power law, and isochrony: converging approaches to movement planning

Two approaches to the study of movement planning were contrasted. Data on the drawing of complex two-dimensional trajectories were used to test whether the covariations of the kinematic and geometrical parameters of the movement formalized by the two-thirds power law and by the isochrony principle (P. Viviani & R. Schneider, 1991) can be derived from the minimum-jerk model hypothesis (T. Flash & N. Hogan, 1985). The convergence of the 2 approaches was satisfactory insofar as the relation between tangential velocity and curvature is concerned (two-thirds power law). Global isochrony could not be deduced from the optimal control hypothesis. Scaling of velocity within movement subunits can instead be derived from the minimum-jerk hypothesis. The implications vis-à-vis the issue of movement planning are discussed with an emphasis on the representation used by the motor control system for coding the intended trajectories.

Cerebral dominance and asynchrony between bimanual two-dimensional movements

The asynchrony of bimanual movements was investigated. Right- and left-handers traced simple geometrical patterns (ellipses) continuously with both hands. All combinations of the direction of rotation in each hand were executed at different rhythms. Geometrically, performances were largely independent of manual dominance. However, by comparing the passage times at homologous positions, the authors found that the dominant hand led the nondominant one by about 25 ms. The asynchrony was affected by neither movement type nor rhythm. The variability of the asynchrony varied along the trajectory, with well-defined maxima and minima. The variability profiles for movements that engaged homologous muscles differed markedly from those that engaged nonhomologous muscles. The authors discuss the hypothesis that bimanual periodic movements are timed by a lateralized functional module and asynchrony is due to the necessity of transmitting time-keeping information to the other hemisphere.

Cerebral dominance and asynchrony between bimanual two-dimensional movements

The asynchrony of bimanual movements was investigated. Right- and left-handers traced simple geometrical patterns (ellipses) continuously with both hands. All combinations of the direction of rotation in each hand were executed at different rhythms. Geometrically, performances were largely independent of manual dominance. However, by comparing the passage times at homologous positions, the authors found that the dominant hand led the nondominant one by about 25 ms. The asynchrony was affected by neither movement type nor rhythm. The variability of the asynchrony varied along the trajectory, with well-defined maxima and minima. The variability profiles for movements that engaged homologous muscles differed markedly from those that engaged nonhomologous muscles. The authors discuss the hypothesis that bimanual periodic movements are timed by a lateralized functional module and asynchrony is due to the necessity of transmitting time-keeping information to the other hemisphere.

Measurement of trypanotolerance criteria and their effect on reproductive performance of N'Dama cattle

One thousand and twenty-eight cow-year records were available from 260 N'Dama cows each having at least 2 years of monthly matching health and performance data over a 5-year period under a medium natural tsetse challenge in Gabon. Four hundred and fifty-eight calf/dam pairs were also available where the calf had been reared to weaning, both had monthly matching records and each cow had weaned at least two calves. Evaluations were carried out on effects of, and linkages between, environmental and stress factors, number and species of trypanosome infections, curative drug treatments given, anaemia measured by packed red cell volume (PCV), and performance measured by calf weaning weight, cow calving rate and cow weight change over the lactation period. Major findings were that over the period from calf birth to weaning, while calves and their dams grazing together had similar numbers of trypanosome infections detected, the Trypanosoma vivax: T. congolense ratios were very different: 1:0.7 in calves; 1:2.8 in cows. This indicated that some ability to control the development of parasitaemia following T. vivax infection might be being acquired, from weaning onwards. In cows, relationships between lowest PCV recorded and curative drug treatments given suggested that between 20 and 32% of trypanosome-infected cows were not being identified by the buffy coat parasitological diagnostic technique. The high level of curative treatment given (to 13.7% of cows over the calendar year, and to 40% of calves from birth to weaning) will have tended to reduce the variance and linkages between aspects of infection and PCV values, especially in calves. In calves, the influence of trypanosome infections, in both calf and dam, on their respective PCV values and hence on calf weaning weight was apparent. There was a 0.91 +/- 0.40 kg increase in calf weaning weight for each 1% increase in calf average PCV, and a 0.95 +/- 0.39 kg increase for each 1% increase in cow average PCV. In cows, there was a similar pathway of influence of T. congolense infection through the PCV values to calving rate--not significant with T. vivax infection. There was a 3.3 +/- 0.65% increase in calving rate for each 1% increase in average PCV. Repeatabilities of performance traits were in the normal range. Repeatabilities of numbers of trypanosome infections detected by the buffy coat technique were too low to have any practical significance. Repeatability of average PCV at 0.40 +/- 0.03 could allow PCV when infected to be used as one criterion of trypanotolerance.

Biological movements look uniform: evidence of motor-perceptual interactions

Six experiments demonstrate a visual dynamic illusion. Previous work has shown that in 2-dimensional (2D) drawing movements, tangential velocity and radius of curvature covary in a constrained manner. The velocity of point stimuli is perceived as uniform if and only if this biological constraint is satisfied. The illusion is conspicuous: The variations of velocity in the stimuli exceed 200%. Yet movements are perceived as uniform. Conversely, 2D stimuli moving at constant velocity are perceived as strongly nonuniform. The illusion is robust: Exposure to true constant velocity fails to suppress it. Results cannot be explained entirely by the kinetic depth effect. The illusion is evidence of a coupling between motor and perceptual processes: Even in the absence of any intention to perform a movement, certain properties of the motor system implicitly influence perceptual interpretation of the visual stimulus.

Relationships between trypanosome infection measured by antigen detection enzyme immunoassays, anaemia and growth in trypanotolerant N'Dama cattle

Relationships were evaluated between trypanosome infection as measured by antigen detection enzyme immunoassays (antigen ELISA), anaemia as determined by average packed red cell volume (PCV), and animal performance as assessed by daily weight gain in 99 N'Dama cattle in Gabon exposed to natural tsetse challenge at 11.5 months of age and recorded 14 times over a 13 week period. Approximately half the animals were found to be infected for an average of five of the 14 times that they were examined: 38% with Trypanosoma congolense, 13% with Trypanosoma vivax and 49% with a mixed infection. Trypanosoma congolense infections had significant deleterious effects on animal growth, while T. vivax infections did not. Animals found on several occasions to be infected with T. congolense had significantly lower PCV values than those demonstrated to be infected on fewer occasions. No relationship was found between mean optical density (OD) values in antigen ELISA and PCV values. Animals capable of maintaining PCV values, even when antigen ELISA positive on a high number of occasions, grew at the same rate as uninfected animals. Animals that could not maintain PCV values when infected had poorer growth. Antigen ELISA has the potential to increase the efficiency of selection of trypanotolerant N'Dama cattle under tsetse challenge in the field, in three main ways. (1) Accurate identification of trypanosome species, especially in mixed species infections, clarifies relations between infection, anaemia and animal performance. (2) Detection of animals antigenaemic without patent parasitaemia could allow individuals with superior ability to control trypanosome infection to be identified. (3) More accurate measurement of the proportion of time an animal is infected allows more accurate evaluation of its anaemia control capability.

Biological movements look uniform: Evidence of motor-perceptual interactions

Six experiments demonstrate a visual dynamic illusion. Previous work has shown that in 2-dimensional (2D) drawing movements, tangential velocity and radius of curvature covary in a constrained manner. The velocity of point stimuli is perceived as uniform if and only if this biological constraint is satisfied. The illusion is conspicuous: The variations of velocity in the stimuli exceed 200%. Yet movements are perceived as uniform. Conversely, 2D stimuli moving at constant velocity are perceived as strongly nonuniform. The illusion is robust: Exposure to true constant velocity fails to suppress it. Results cannot be explained entirely by the kinetic depth effect. The illusion is evidence of a coupling between motor and perceptual processes: Even in the absence of any intention to perform a movement, certain properties of the motor system implicitly influence perceptual interpretation of the visual stimulus.

A developmental study of the relationship between geometry and kinematics in drawing movements

Trajectory and kinematics of drawing movements are mutually constrained by functional relationships that reduce the degrees of freedom of the hand-arm system. Previous investigations of these relationships are extended here by considering their development in children between 5 and 12 years of age. Performances in a simple motor task--the continuous tracing of elliptic trajectories--demonstrate that both the phenomenon of isochrony (increase of the average movement velocity with the linear extent of the trajectory) and the so-called two-thirds power law (relation between tangential velocity and curvature) are qualitatively present already at the age of 5. The quantitative aspects of these regularities evolve with age, however, and steady-state adult performance is not attained even by the oldest children. The power-law formalism developed in previous reports is generalized to encompass these developmental aspects of the control of movement.

The effect of movement velocity on form perception: geometric illusions in dynamic displays

We investigated the effects of movement velocity on the perception of simple geometric trajectories. We show that when an ellipse is traced by the continuous displacement of a spot against an empty background, the subjective aspect ratio (R = vertical axis/horizontal axis) of the figure depends on the law of motion of the spot. If the tangential velocity of the spot is constant, very large and subject-specific biases emerge in the perception of the aspect ratio. If the tangential velocity of the spot is made equal to that of an elliptic motion with aspect ratio R less than 1, and resulting from the vectorial composition of two harmonic functions (Lissajous motion) there is a general trend to perceive the ellipse as being flatter than in reality. The effect, however, is not symmetric: when the velocity follows a Lissajous modulation with R greater than 1, highly significant biases are still present in most subjects, but no common trend emerges from the experimental population. The results are discussed in the context of recent findings on the relationship between form and kinematics in spontaneous human movements.

Spontaneous Covariations of Movement Parameters in 5- to 7-Year-Old Boys

The kinematic parameters of to and fro forearm movements in the horizontal plane were investigated in 5- to 7-year-old boys. In one condition, the period of the movements was induced by an acoustic stimulus, while the amplitude was left free. In a second condition, the amplitude of the swing was suggested by a visual frame, but the movement was self-paced. In both conditions, the unconstrained variable (amplitude and period, respectively) was found to covary spontaneously with the constrained variable. The results suggest that, within the age range considered here, motor control processes do not conceive of amplitude and velocity as two independent variables.

Segmentation and coupling in complex movements

In two experiments we explore the structure of complex sequences of drawing movements. We find that in these movements a single parameter--the velocity gain factor--relates the geometrical and kinematic aspects of the movement trajectory via a two-thirds power law. In Experiment 1 we investigate the relation between the velocity gain factor and the linear extent of the trajectory. In Experiment 2 we demonstrate that the gain factor provides a criterion for segmenting the movement into distinct units of motor action, and we investigate the effects of the speed of execution on this segmentation. A theoretical analysis shows that the results of both Experiments 1 and 2 can be given a unitary interpretation by assuming a coupling function of variable strength between segments. The general problem of representing motor programs is discussed within this theoretical framework.

Segmentation and coupling in complex movements

In two experiments we explore the structure of complex sequences of drawing movements. We find that in these movements a single parameter--the velocity gain factor--relates the geometrical and kinematic aspects of the movement trajectory via a two-thirds power law. In Experiment 1 we investigate the relation between the velocity gain factor and the linear extent of the trajectory. In Experiment 2 we demonstrate that the gain factor provides a criterion for segmenting the movement into distinct units of motor action, and we investigate the effects of the speed of execution on this segmentation. A theoretical analysis shows that the results of both Experiments 1 and 2 can be given a unitary interpretation by assuming a coupling function of variable strength between segments. The general problem of representing motor programs is discussed within this theoretical framework.

The relation between linear extent and velocity in drawing movements

The speed of execution of complex movements depends on both the local, differential properties of the trajectory and on some of its more global metric parameters. The effects of these global factors were studied in free, writing-like movements with either piece-wise constant, or regularly changing curvature. It is demonstrated that the tangential velocity of the pen's tip is tightly correlated, through a power function, with the total linear extent of the trajectory (perimeter). Thus, a strong tendency exists to keep the execution time of these complex trajectories independent of the movement size (isochrony). Furthermore, it is shown that the average tangential velocity over identifiable segments of the trajectory also depends on the corresponding average curvature. The implications of these results vis-à-vis the central representation and planning of movements are discussed.

Motor Strategies in Lifting Movements

The experiment compares the performances of children six to nine years old and adults in a simple, monoarticular lifting task. Overt behaviors, as described by the kinematic features of the movement, do not differ qualitatively in the two groups. The patterns of motor commands, as expressed by the electromyographic recordings, are however strikingly different. Adults plan the movement with a careful balance between agonist muscle activity and passive, viscoelastic forces, whereas children use both agonist and antagonist active forces. It is argued that the motor strategy adopted by adults depends upon an internal representation of the properties of the motor system and of the size/weight covariation in natural objects, and that this representation is not yet fully developed at nine years of age.

Saccadic eye movements to peripherally discriminated visual targets

Two experiments required subjects to identify a peripheral target embedded among nontarget stimuli and fixate it as quickly as possible with a single saccadic eye movement. Experiment 1 varied both the target distance and its angular position between trials; the mean oculomotor latency, the proportion of erroneous movements, and the proportion of (correct) movements followed by a corrective saccade all increased as a function of target distance. Experiment 2 held target distance constant (12.7 degrees) and used verbal instructions to manipulate the speed and accuracy of the subject's oculomotor performance between conditions. The speed/accuracy trade-off was similar for all subjects. The reduced uncertainty about target distance in Experiment 2 made each subject's oculomotor performance more efficient. Error trials not only included apparent perceptual errors (initial movements to nontarget stimuli) but also motor errors - that is, instances when the initial erroneous movement was followed, with an extremely short latency, by a large saccade to the target. The characteristics of these motor errors suggest that the saccade is not planned in terms of its amplitude and direction in retinal coordinates.