Interference between oculomotor and postural tasks in 7-8-year-old children and adults.

Several studies in adults having observed the effect of eye movements on postural control provided contradictory results. In the present study, we explored the effect of various oculomotor tasks on postural control and the effect of different postural tasks on eye movements in eleven children (7.8 ± 0.5 years) and nine adults (30.4 ± 6.3 years). To vary the difficulty of the oculomotor task, three conditions were tested: fixation, prosaccades (reactive saccades made toward the target) and antisaccades (voluntary saccades made in the direction opposite to the visual target). To vary the difficulty of postural control, two postural tasks were tested: Standard Romberg (SR) and Tandem Romberg (TR). Postural difficulty did not affect oculomotor behavior, except by lengthening adults' latencies in the prosaccade task. For both groups, postural control was altered in the antisaccade task as compared to fixation and prosaccade tasks. Moreover, a ceiling effect was found in the more complex postural task. This study highlighted a cortical interference between oculomotor and postural control systems.

A top-down synthesis route to ultrasmall multifunctional Gd-based silica nanoparticles for theranostic applications.

New, ultrasmall nanoparticles with sizes below 5 nm have been obtained. These small rigid platforms (SRP) are composed of a polysiloxane matrix with DOTAGA (1,4,7,10-tetraazacyclododecane-1-glutaric anhydride-4,7,10-triacetic acid)-Gd(3+) chelates on their surface. They have been synthesised by an original top-down process: 1) formation of a gadolinium oxide Gd2O3 core, 2) encapsulation in a polysiloxane shell grafted with DOTAGA ligands, 3) dissolution of the gadolinium oxide core due to chelation of Gd(3+) by DOTAGA ligands and 4) polysiloxane fragmentation. These nanoparticles have been fully characterised using photon correlation spectroscopy (PCS), transmission electron microscopy (TEM), a superconducting quantum interference device (SQUID) and electron paramagnetic resonance (EPR) to demonstrate the dissolution of the oxide core and by inductively coupled plasma mass spectrometry (ICP-MS), mass spectrometry, fluorescence spectroscopy, (29)Si solid-state NMR, (1)H NMR and diffusion ordered spectroscopy (DOSY) to determine the nanoparticle composition. Relaxivity measurements gave a longitudinal relaxivity r1 of 11.9 s(-1) mM(-1) per Gd at 60 MHz. Finally, potentiometric titrations showed that Gd(3+) is strongly chelated to DOTAGA (complexation constant logß110 =24.78) and cellular tests confirmed the that nanoconstructs had a very low toxicity. Moreover, SRPs are excreted from the body by renal clearance. Their efficiency as contrast agents for MRI has been proved and they are promising candidates as sensitising agents for image-guided radiotherapy.

Faecalibacterium prausnitzii supernatant improves intestinal barrier function in mice DSS colitis.

OBJECTIVE. The intestinal microbiota plays a substantial role in the pathogenesis of inflammatory bowel disease (IBD). Faecalibacterium prausnitzii (FP) is underrepresented in IBD patients and have been suggested to have anti-inflammatory effects in mice. Increased intestinal permeability is common in IBD but the relationship between FP and intestinal barrier function has not been investigated. Our aim was to study treatment with FP supernatant on intestinal barrier function in a dextran sodium sulfate (DSS) colitis mice model. MATERIAL AND METHODS. C57BL/6 mice received 3% DSS in tap water ad libitum during five days to induce colitis. From day 3 the mice received a daily gavage with FP supernatant or broth during seven days. Ileum and colon were mounted in Ussing chambers for permeability studies with (51)Cr-EDTA and Escherichia coli K-12. Colon was saved for Western blot analyses of tight junction proteins. RESULTS. DSS-treated mice showed significant weight loss and colon shortening. Gavage with FP supernatant resulted in a quicker recovery after DSS treatment and less extensive colonic shortening. Ileal mucosa of DSS mice showed a significant increase in (51)Cr-EDTA-passage compared to controls. (51)Cr-EDTA passage was significantly decreased in mice receiving FP supernatant. No significant differences were observed in passage of E. coli K12. Western blots showed a trend to increased claudin-1 and claudin-2 expressions in DSS mice. CONCLUSIONS. Supernatant of FP enhances the intestinal barrier function by affecting paracellular permeability, and may thereby attenuate the severity of DSS-induced colitis in mice. These findings suggest a potential role of FP in the treatment of IBD.

Differing effects of prosaccades and antisaccades on postural stability.

The goal of the study was to examine the effect of different types of eye movements on postural stability. Ten healthy young adults (25 ± 3 years) participated in the study. Postural control was measured by the TechnoConcept© platform and recorded in Standard Romberg and Tandem Romberg conditions while participants performed five oculomotor tasks: two fixation tasks (central fixation cross, without and with distractors), two prosaccade tasks toward peripheral targets displayed 4° to the left or to the right of the fixation cross (reactive saccades induced by a gap 0 ms paradigm and voluntary saccades induced by an overlap 600 ms paradigm) and one antisaccade task (voluntary saccade made in the opposite direction of the visual target). The surface, the length, and the mean speed of the center of pressure were analyzed. We found that saccadic eye movements improved postural stability with respect to the fixation tasks. Furthermore, antisaccades were found to decrease postural stability compared to prosaccades (reactive as well as voluntary saccades). This result is in line with the U-shaped nonlinear model described by Lacour et al. (Neurophysiol Clin 38:411-421, 2008), showing that a secondary task performed during a postural task could increase (prosaccade task) or decrease (antisacade task) postural stability depending on its complexity. We suggest that the different degree of attentional resources needed for performing prosaccade or antisaccade tasks are, most likely, responsible for the different effect on postural control.

Cyclam-methylbenzimidazole: a selective OFF-ON fluorescent sensor for zinc.

The coordination properties and the photophysical response of a new cyclam fluorescent probe for Zn(II), [L1H: 1-(benzimidazol-2-ylmethyl]-1,4, 8,11-tetraazacyclotetradecane] toward Cu(II), Zn(II), and Cd(II) are reported. The stability constants of the corresponding complexes were determined by means of potentiometric measurements in aqueous solution. The fluorescence of L1H was quenched by the presence of Cu(II), and L1H behaves as an OFF-ON sensor for Zn(II) even in the presence of a wide range of biological divalent cations. Furthermore, on addition of successive amounts of Zn(II), the fluorescence emission of L1H increases linearly by a factor of 12. This can be correlated to the efficient Zn(II) binding of L1H and to the participation of all the amine functions in the metal coordination which prevents the photoinduced electron transfer (PET) effect and promotes a good chelation-enhanced fluorescence (CHEF) effect; this confers to the cyclam probe better sensing properties than the cyclen ionophore.

Effects of dual tasking on postural and gait performances in children with cerebral palsy and healthy children.

Simultaneous execution of motor and cognitive tasks is embedded in the daily life of children. 53 children of 7-12 years and 22 adults (study 1), 20 healthy children and 20 children of 7-12 years with cerebral palsy (study 2) performed a Stroop-animal task simultaneously with a standing or a walking task in order to determine the attentional demand of postural control and locomotion. Dual-task cost decreased with advancing age in healthy children during balance. CP and healthy children were similarly affected by dual-task constraints during standing and walking. Children with diplegia were more affected by the DT during the postural task than children with hemiplegia. We found that adults could benefit from dual-tasking for standing. The integrated model of task prioritization might explain our results regarding postural reserve of each population.

Study of Iron Piperazine-Based Chelators as Potential Siderophore Mimetics.

Gram-negative bacteria's resistance such as Pseudomonas aeruginosa and the Burkholderia group to conventional antibiotics leads to therapeutic failure. Use of siderophores as Trojan horses to internalize antibacterial agents or toxic metals within bacteria is a promising strategy to overcome resistance phenomenon. To combat the Pseudomonas sp, we have synthesized and studied two piperazine-based siderophore mimetics carrying either catecholate moieties (1) or hydroxypyridinone groups (2) as iron chelators. These siderophore-like molecules were prepared in no more than four steps with good global yields. The physicochemical study has highlighted a strong iron affinity since their pFe values were higher than 20. 1 possesses even a pFe value superior than those of pyoverdine, the P. aeruginosa endogenous siderophore, suggesting its potential ability to compete with it. At physiological pH, 1 forms mainly a 2:3 complex with iron, whereas two species are observed for 2. Unfortunately, the corresponding Ga(III)-1 and 2 complexes showed no antibacterial activity against P. aeruginosa DSM 1117 strain. The evaluation of their siderophore-like activity showed that 1 and 2 could be internalized by the bacteria.

Anticipatory postural adjustments associated with a forward leg raising in children: effects of age, segmental acceleration and sensory context.

OBJECTIVE: The purpose of this study was to determine the influence of age, segmental acceleration and sensory context on anticipatory postural adjustments (APAs) in a forward leg raising task. METHODS: Three groups of 11 children, aged 8, 10 and 12, and 12 adults, aged 20 to 26, were instructed to perform this movement at maximal (MAXIMAL) and sub-maximal segmental accelerations and in normal (CONTROL), no vision (NV) and perturbed proprioception conditions (VIB). The generation and calibration of APAs were examined through the centre of foot pressure displacements: The onset, duration and amplitude of APAs were particularly explored. The EMG activity of the tibialis anterior (TA(stance)) and gastrocnemius medialis (G(stance)) of the stance leg was also recorded. RESULTS: Two phases were clearly identified on the ML axis: A thrust and an unloading phase. Effect of age: At 8 and 10, (1) the unloading duration was shorter, and (2) the onset of APAs on the ML axis appeared later than in 12-year-old children and in adults. Effect of the segmental acceleration: (1) a greater amplitude of the thrust and unloading phases, (2) a shorter unloading duration, and (3) a later onset of ML APAs and of the TA(stance) activity were observed at maximal acceleration in all groups. Effect of the sensory context: No difference was found between the CONTROL and NV conditions. When the proprioceptive feedback was altered, (1) the thrust and unloading durations increased, and (2) the onset of the APAs on the ML axis occurred earlier. CONCLUSION: All children exhibited an anticipatory behaviour, but the adults' behaviour was reached at 12 only. Our results also indicated a change in the generation and calibration of APAs in the VIB condition, suggesting that proprioceptive information is essential for both dimensions of the APAs. SIGNIFICANCE: The development of the APAs was not related to the segmental acceleration and to the sensory context of the forthcoming movement in children aged 8-12. It is very likely that the participants built up an internal representation of this movement.

Effects of attentional focus on postural sway in children and adults.

The present study examined, in children aged 4-11 and in adults, the postural control modifications when attention was oriented voluntary on postural sway. Since (1) there are less attentional resources in children than in adults, (2) the selective attention processing improves with age, i.e., children use a different strategy to focus their attention than adults, and (3) adults' postural stability decreases when attention is focused on postural sway, we hypothesized that postural stability was less affected in children than in adults when attention was focused on postural sway. Fourty four children aged 4- to 11-year-old and 11 adults participated in the experiments. The postural control task was executed in a Romberg position. Two experimental conditions were presented to the subjects, (1) to look at a video on a TV screen without instruction about the posture, and (2) to fixate a cross placed at the center of the TV screen with the instruction to remain as stable as possible. Postural performance was measured by means of a force platform. Results from this study (1) confirmed a non-monotonic improvement of postural stability during the ontogenetic period without reaching the adults' level at the age of 11, (2) suggested that children, aged 4-11, are able to focus their attention on the control of posture, and (3) showed that the automatic control of posture increases postural stability since the age of 4.

Dual-task study of cognitive and postural interference in 7-year-olds and adults.

The study examined, in children aged 7 and adults, the postural control when a cognitive task (modified Stroop) of varying level of difficulty is executed simultaneously. Postural difficulty also varied (with or without vibrations of the ankle joint). We hypothesized that children's performance was more affected than adults', when the difficulty of the cognitive and postural tasks increased. Results (i) demonstrated that the presence of a concurrent cognitive task affected postural sway at all ages; (ii) confirmed that the interference between mental activity and postural control can be attributed mainly to general capacity limitations and (iii) showed a degradation of the postural criteria in children but not of the cognitive ones, when the postural condition was constraining.

Attentional load of walking in children aged 7-12 and in adults.

The amount of attentional resources necessary to walk in children, and how they evolve during childhood remains unclear. This study examined children's gait parameters in different dual-task conditions. 53 children, divided into two age groups (7-9 and 10-12 years old), and 18 adults walked on a mat in three different cognitive conditions: watching a video (video condition), listening its soundtrack (audio condition), and without any additional task (control condition). Questions were asked at the end of the video and audio conditions to make sure that participants were paying attention to the stimuli. A GAITRite® system was used for recording the gait data. Results showed an increase of velocity and step duration, and a decrease of cadence and percentage of double limb support duration from 7 years of age to adulthood during dual-task walking compared with single-task walking. This improvement seemed to be linear from 7 years to adults' age. The interference of dual-task on gait was larger for the video than for the auditory task and decreased with age. We concluded that walking requires a significant amount of attentional resources in children and that children rely more than adults on visual processes for walking.

Effects of emotional videos on postural control in children.

The link between emotions and postural control has been rather unexplored in children. The objective of the present study was to establish whether the projection of pleasant and unpleasant videos with similar arousal would lead to specific postural responses such as postural freezing, aversive or appetitive behaviours as a function of age. We hypothesized that postural sway would similarly increase with the viewing of high arousal videos in children and adults, whatever the emotional context. 40 children participated in the study and were divided into two groups of age: group 7-9 years (n=23; mean age=8 years ± 0.7) and group 10-12 years (n=17; mean age=11 years ± 0.7). 19 adults (mean age=25.8 years ± 4.4) also took part in the experiment. They viewed emotional videos while standing still on a force platform. Centre of foot pressure (CoP) displacements were analysed. Antero-posterior, medio-lateral mean speed and sway path length increased similarly with the viewing of high arousal movies in the younger, older children, and adults. Our findings suggest that the development of postural control is not influenced by the maturation of the emotional processing.

Developmental changes of static standing balance in children.

The purpose of the present experiment was to investigate the time course by which children aged 6-, 8- and 10-year-old adapt and maintain their static balance. Participants (N=30) were required to stand on a force platform with their eyes closed. Ten adult subjects served as a reference group. We analyzed moment-to-moment modifications of quiet stance equilibrium by measuring the range and speed of the center of foot pressure (COP) displacements over time (i.e., periods of 2 s). Results showed that: (1) with age, the range of the COP decreased non-monotonically, with a maximum at 8 years of age, whereas the speed of the COP decreased linearly from 6 to 10 years of age, and (2) over time, both parameters decreased and stabilized, similarly for all age groups, suggesting that the processes underlying the maintenance of an optimal postural stability are mature at least as soon as 6 years of age.

Effects of foreperiod duration on anticipatory postural adjustments: determination of an optimal preparation in standing and sitting for a raising arm movement.

The purpose of the present experiment was to examine the motor and postural preparation processes evolving during the foreperiod (known to be optimal at 500 ms in sitting) in a voluntary upper limb movement executed while standing. The foreperiod duration (300, 500, 700 and 900 ms) and the postural conditions (sitting versus standing) were manipulated using a priming procedure. Two types of prime were provided: (1) a prime giving valid information on the side of the raising arm movement to execute, and (2) a prime giving non-valid information (prime opposite to the required side). In a sitting and standing condition, eight normal subjects performed a raising arm movement with a 1 kg load at the level of the wrist. Premotor time and acceleration of arm movement were recorded in the two postural conditions. In the standing condition, anticipatory postural adjustments (APAs) were also quantified using the relative latency of electromyographic (EMG) data and the centre of foot pressure (CoP) displacements. Results (1) showed that the optimal foreperiod duration (i.e., leading to the shortest premotor time) increased as a function of postural conditions (500 versus 700 ms in the sitting and standing conditions, respectively), and (2) emphasized the existence of a temporal modulation in the central organization of the postural and focal commands according to the foreperiod duration.

Role of proprioceptive information in movement programming and control in 5 to 11-year old children.

The role of proprioceptive inputs in the control of goal-directed movements was examined, by means of the tendon vibration technique, in 5 to 11-year old children performing a serial pointing task. Children pointed, with movements of various amplitudes and at various positions, by alternating wrist flexions and extensions. Tendon vibration was applied to both agonist and antagonist muscles to perturb relevant muscular proprioceptive inputs during the static or dynamic phase of the task, i.e., during stops on targets or during movement execution. Constant and variable amplitude errors as well as constant position error were evaluated. Vibratory perturbation applied during movement execution resulted in a similar reduction in movement amplitude, yielding an increased constant error in all age groups and a systematic position error in the direction of the movement starting point. Perturbing proprioception during static phases preceding movement resulted in an age-related increase in the variable amplitude error, which was maximal in 5-year old children performing extension movements. The results were interpreted in terms of the use of proprioceptive information in the feedforward and feedback based components of movement control in children. In particular, the results indicated (1) developmental changes in the relative weighting of each component, (2) an increased capacity to move from one strategy to the other, depending on the availability of information, and (3) developmental changes from an alternated to an integrated control of amplitude and position in serial pointing.

Thermodynamic stability and kinetic inertness of a Gd-DTPA bisamide complex grafted onto gold nanoparticles.

Gold nanoparticles coated by gadolinium (III) chelates (Au@DTDTPA) where DTDTPA is a dithiolated bisamide derivative of diethylenetriamine-N,N,N',N'',N''-pentaacetic acid (DTPA), constituted contrast agents for both X-ray computed tomography and magnetic resonance imaging. In an MRI context, highly stable Gd(3+) complexes are needed for in vivo applications. Thus, knowledge of the thermodynamic stability and kinetic inertness of these chelates, when grafted onto gold nanoparticles, is crucial since bisamide DTPA chelates are usually less suited for Gd(3+) coordination than DTPA. Therefore, these parameters were evaluated by means of potentiometric titrations and relaxivity measurements. The results showed that, when the chelates were grafted onto the nanoparticle, not only their thermodynamic stability but also their kinetic inertness were improved. These positive effects were correlated to the chelate packing at the nanoparticle surface that stabilized the corresponding Gd(3+) complexes and greatly enhanced their kinetic inertness.

Foreperiod duration and motor preparation during childhood.

The purpose of this experiment was to examine the development of motor preparation across three groups of children aged 6, 8 and 10 years old. The foreperiod duration (500, 1000, 2000 and 4000 ms) and the motor preparation conditions were manipulated using a priming procedure. Two type of primes were provided: (1), a prime carrying no advanced information (neutral condition); and (2), a prime giving advanced information on the nature of the motor response to execute, allowing the participant to prepare for it (selective condition). Reaction time and response errors were analyzed. Results showed that under both conditions, the optimal motor preparation was reached within the same time frame which decreased as age increased. As to the optimal alertness level (neutral preparation), it is maintained longer as age increases, whereas the optimal motor programming level (selective preparation) is reached only for specific foreperiod duration.

Effects of temporal and/or spatial instructions on the speed-accuracy trade-off of pointing movements in children.

The present experiment examined in a visuo-manual task the effects of verbal instructions on the speed/accuracy trade-off across children aged 6, 8 and 10 years and adults. Three different verbal instructions (speed, accuracy and speed-accuracy) had to be respected to perform a pointing task. Analysis of reaction time (RT), movement time (MT) and percentage of targets reach showed that: (1) whatever the age, children were able to comply with the verbal instructions to adapt the velocity and/or the precision of their response (initiation and movement execution); (2) the main age-related difference of the speed-accuracy trade-off concerned the temporal (MT) but not the accuracy (targets reach) characteristics of the pointing movements; and (3) in the older children and even more precisely in adults, a temporal deficit was observed when the accuracy of aiming was required. This deficit increased as accuracy increased. These results were discussed within the theoretical frameworks of the developmental speed processing model proposed by Kail [Psychol. Bull., 109(3) (1991) 490-501] for RT data, and the speed-accuracy trade-off model proposed by Pachella [Pachella, R.G., The interpretation of reaction time in information-processing research, in, Kantowitz, B. (ed) Human Information Processing: Tutorial in Performance and Recognition, Erlbaum, (1974) 41-82] for MT and targets reach data.

Aged-related differences in the attentional cost of pointing movements.

The aim of the present study was to analyze, in children aged 6, 8 and 11, the developmental trend of the attentional cost related to the programming and execution of pointing movements, using a dual-task paradigm. Our results showed that the attentional cost associated to the programming and the first phase of the pointing movement decreased non linearly with age, in particular a plateau between 8 and 11 was observed. This confirmed that the developmental trend of the control of pointing movements is characterized by a no monotonic evolution in which feedforward processes were predominantly used in the younger children, feedback processes were predominantly used in older children (since age 8), and one-line over feedforward processes were used in adults.

Predictable postural perturbation in premotor and motor components of reaction time.

The aim of the present experiment was to study the central control of posture and movement coordination. Subjects' task was voluntarily to raise their arms in response to a visual signal, this movement generating an unloading in which the weight of the load (0 gm, 1500 gm, 3000 gm, or 4500 gm) was known in advance. Thus, subjects could predict the postural perturbation generated by the unloading. Analysis showed an effect of the unloading conditions: in the 0-gm and 1500-gm conditions, reaction time (RT) was longer than in the 3000-gm and 4500-gm conditions. This decrease in RT was exclusively due to a reduction of the premotor time, confirming the posturokinetic coordination in the programming processes. The implications of the decrease in premotor time with the increase of the perturbation for the posture/movement coordination strategies are also discussed.