Cognitive load affects postural control in children

Interaction between visual working memory and upright postural control in young adults: an event-related potential study based on the n-back paradigm

As a part of the overall information-processing system of the brain, postural control is related to the cognitive processes of working memory. Previous studies have suggested that cognitive tasks and postural control processes can compete for resources in common brain areas, although there is an "inverted U" relationship between arousal level and behavioral control - the arousal level of individuals changes when performing cognitive tasks. However, the exact neural connections between the two are unclear. This may be related to the nature of cognitive tasks. Some studies believe that posture occupies not only spatial information processing resources but also visual non-spatial information processing resources. Other studies believe that posture control only occupies spatial information processing resources in the central system, but does not occupy non-spatial information processing resources. Previous studies used different cognitive task materials and reached different conclusions. In this study, we used the same visuospatial and non-spatial materials, the n-back visual working memory paradigm, the event-related potential technique to investigate the effects of visuospatial and non-spatial working memory tasks on adolescents' postural control under different cognitive loads. The results of this study showed that in both visuospatial and non-spatial conditions, the N1 effect of the parieto-occipital lobe was larger during upright posture than in the sitting position (160-180 ms), the P300 effect of the central parieto-occipital region (280-460 ms) was induced by working memory in different postures, and the P300 wave amplitude was higher in the sitting position than in the upright position. We demonstrated that upright postural control enhances early selective attention but interferes with central memory encoding, thus confirming that postural control and visuospatial and non-spatial working memory share brain regions and compete with each other.

Comparative Analysis of Physical Activity, Performance-Related Health, and Academic Achievements in 11-to-13-Year-Old Schoolchildren in Qatar

Age-related differences in physical activity (PA), maturity status (PHV), physical performance (PP), and academic achievement (AA) among schoolchildren in Qatar were examined. Sixty-nine students from a school in Doha were categorized into three equal (n = 23) groups: 11-year-old students (U11; male: n = 14), 12-year-old students (U12: male: n = 7), and 13-year-old students (U13: male: n = 11). The testing process comprised a medicine ball throw, Stork balance test, hand grip strength test, the T-half test (PP), GPA in Arabic, mathematics, science (AA), International Physical Activity Questionnaire Short Form (PA), and Moore's equations (PHV). Relevant age-related differences (p < 0.001) were identified in mathematics, science, the T-half test, maturity, and arm span. Notably, differences between adjacent age groups were evident between U11 and U12, concerning arm span, maturity, mathematics, and science, and between U12 and U13 (the T-half test, mathematics, science). Concerning AP, the performance maxima were calculated for U12 (mathematics, science) and U11 (Arabic). Regarding PP, performance maxima were only observed for U13. Except for the moderate level, the highest levels of PA were detected in U13. Maturity status and anthropometric parameters did not differ significantly between age groups. However, AA demonstrated the most notable age-related differences. Specifically, mathematics showed substantial differences between adjacent age groups.

Effects of the BalanCI on Working Memory and Balance in Children and Young Adults With Cochleovestibular Dysfunction

OBJECTIVES

This study aimed to: (1) determine the interaction between cognitive load and balance in children and young adults with bilateral cochleovestibular dysfunction who use bilateral cochlear implants (CIs) and (2) determine the effect of an auditory balance prosthesis (the BalanCI) on this interaction. Many (20 to 70%) children with sensorineural hearing loss experience some degree of vestibular loss, leading to poorer balance. Poor balance could have effects on cognitive resource allocation which might be alleviated by the BalanCI as it translates head-referenced cues into electrical pulses delivered through the CI. It is hypothesized that children and young adults with cochleovestibular dysfunction will demonstrate greater dual-task costs than typically-developing children during dual balance-cognition tasks, and that BalanCI use will improve performance on these tasks.

DESIGN

Study participants were 15 typically-developing children (control group: mean age ± SD = 13.6 ± 2.75 years, 6 females) and 10 children and young adults who use bilateral CIs and have vestibular dysfunction (CI-V group: mean age ± SD=20.6 ± 5.36 years, 7 females). Participants completed two working memory tasks (backward auditory verbal digit span task and backward visuospatial dot matrix task) during three balance conditions: seated, standing in tandem stance with the BalanCI off, and standing in tandem stance with the BalanCI on. Working memory performance was quantified as total number of correct trials achieved. Postural stability was quantified as translational and rotational path length of motion capture markers worn on the head, upper body, pelvis, and feet, normalized by trial time.

RESULTS

Relative to the control group, children and young adults in the CI-V group exhibited poorer overall working memory across all balance conditions ( p = 0.03), poorer translational postural stability (larger translational path length) during both verbal and visuospatial working memory tasks ( p < 0.001), and poorer rotational stability (larger rotational path length) during the verbal working memory task ( p = 0.026). The CI-V group also exhibited poorer translational ( p = 0.004) and rotational ( p < 0.001) postural stability during the backward verbal digit span task than backward visuospatial dot matrix task; BalanCI use reduced this stability difference between verbal and visuospatial working memory tasks for translational stability overall ( p > 0.9), as well as for rotational stability during the maximum working memory span (highest load) participants achieved in each task ( p = 0.91).

CONCLUSIONS

Balance and working memory were impaired in the CI-V group compared with the control group. The BalanCI offered subtle improvements in stability in the CI-V group during a backward verbal working memory task, without producing a negative effect on working memory outcomes. This study supports the feasibility of the BalanCI as a balance prosthesis for individuals with cochleovestibular impairments.

Focused attention as a new sitter: How do infants balance it all?

This study investigated the impact of postural control on infants' Focused Attention (FA). Study 1 examined whether and how sitting independently versus with support impacted 6- to 8-month-old infants' ability to focus attention during object exploration. FA measures did not depend on support condition. However, sitting experience was significantly negatively correlated with FA measures in the supported condition, suggesting that infants with more sitting experience performed fewer exploratory movements, possibly due to faster information processing ability compared to infants with less sitting experience. These unexpected findings prompted an exploration of more subtle looking behaviors during FA in Study 2-a case study of three infants who wore a head-mounted eye-tracker during an FA task. The ability to rapidly shift visual attention was key to gathering environmental information useful for problem solving-an interpretation that is supported by prior findings of the relationship between fast looks and faster information processing.

Balance rehabilitation for postural control in children with Autism Spectrum Disorder: A two-case report study

OBJECTIVE

This study aimed to investigate the effect of balance rehabilitation on postural control in both low and increased cognitive load conditions in two children with Autism Spectrum Disorders (ASD).

METHODS

Two children diagnosed with ASD participated in a 4-week personalized balance rehabilitation program with two sessions per week. We assessed postural control in two single task (ST) conditions with low cognitive load: Eyes Closed (EC), Eyes Open (EO); and in five increased cognitive load conditions. Those dual task (DT) conditions consisted of presenting images representing a neutral condition, sadness, anger, happiness, and fear. Postural control parameters (surface, velocity, medio-lateral and antero-posterior sway amplitudes of the center of pressure (CoP)) were collected by a posturographic platform before and after the balance rehabilitation.

RESULTS

The rehabilitation program resulted in a 30-96% improvement of postural control parameters in the ST condition for both participants. In DT, participant 1 progressed on all conditions while participant 2 progressed on 3 of the 5 conditions (sadness, anger and fear).

CONCLUSION

This suggests that these two children with ASD improved their balance control in both low and increased cognitive load conditions. These encouraging results need to be replicated before recommending balance rehabilitation as standard health rehabilitation in children with ASD.

Dual-task affects postural balance performance in children with intellectual disability

BACKGROUND

Dual-task designs have been used to study the degree of automatic and controlled processing involved in postural balance. The aim of the present study was to explore postural balance performance during dual-task condition in children with intellectual disability compared to those with typical development.

METHODS

Fifteen children with intellectual disability aged from 7 to 12 years old and fifteen age-matched children with typical development participated in this study. Participants were asked to maintain static balance on a force platform during a baseline condition (single task) and while performing the Picture Recognition Memory Test (dual-task condition).

RESULTS

The results showed that dual-task similarly affects postural performance of both typically developing children and those with intellectual disability (p < .001).

CONCLUSIONS

Children with intellectual disability and children with typical development have difficulties in maintaining their balance when carrying out a concurrent cognitive task. Intellectual disability did not lead to a more strongly compromised balance performance in dual-task situation.

Cognitive-Motor Interference during Dual Tasks in Blind Children

The aim of the present study was to compare the dual-task (DT) performance in blind children with sighted ones while concurrently performing a motor task (upright standing) with cognitive (Letter fluency (LF) or Category fluency (CF)) tasks. The Center of pressure mean velocity (CoP_Vm) and the cognitive performances were recorded during single (ST) and DT conditions. Results showed that, for both groups, CoP_Vm values increased significantly (p < 0.05) in the DT compared to ST condition. The CoP_Vm values were significantly (p < 0.001) higher in blind children, compared to controls only in the DT-CF condition. In conclusion, balance performance of blind and typically developed children is affected by dual tasking. Interference between motor and cognitive tasks has more pronounced effects on balance performance in blind children, compared to controls. This difference was observed only when performing the CF task concurrently with the postural balance task.

Effects of motor and cognitive manipulation on the dual-task costs of center of pressure displacement in children, adolescents and young adults: A cross-sectional study

BACKGROUND

Dual-task paradigms allow to establish a relationship between motor and cognitive performance. The attentional resources needed to accomplish dual-tasks are influenced by age and task complexity. We investigated the dual-task costs for center of pressure displacement following manipulated motor and cognitive tasks in children, adolescents and young-adults.

METHODS

Thirty children, 24 adolescents and 32 young-adults performed motor (postural stability) and cognitive (arithmetic) tasks under single and dual-task conditions. Complexity was manipulated by changing the base of support (standard, narrow, standard_on_foam, narrow_on_foam) for motor tasks and the difficulty level of cognitive tasks via serial subtraction (by 5 and by 3). Dual-task costs were calculated based on area and velocity of center of pressure.

FINDINGS

Dual-task costs based on area during easy cognitive tasks were lower for children than young-adults. Under all the cognitive conditions, dual-task costs were lower on narrow than on standard bases of support. For all the tested bases of support, dual-task costs based on velocity were lower for more complex cognitive tasks than for easy tasks.

INTERPRETATION

In children, more than in adults, dual-task demanded central adaptations which increased area of center of pressure displacement. Mechanical reasons, which might limit the increase in center of pressure displacement when dual-tasking, may explain the lower dual-task costs in narrow bases compared to standard ones. Possibly, high cognitive demands may lead the participants to prioritize the motor task to keep balance, resulting in smaller increases in center of pressure displacement velocity during dual-task when compared to easier cognitive tasks.

Effects of Fatigue on Balance Recovery From Unexpected Trips

OBJECTIVE

The objective was to examine how physical fatigue and mental fatigue affected balance recovery from unexpected trips.

BACKGROUND

Trips are the leading cause for occupational falls that are a multifactorial problem. Recognizing risk factors is the first step in accident control. Fatigue is one of the most common task-related risk factors for occupational falls. Fatigue typically can be divided into physical fatigue and mental fatigue, both of which are common in occupational settings.

METHOD

One hundred eight young volunteers participated in the experiment. They were evenly divided into three groups: no fatigue group, physical fatigue group, and mental fatigue group. Each participant performed four walking trials on a linear walkway at their self-selected normal speed. The first three trials were normal walking trials. A trip was induced to participants in the fourth walking trial using a metal pole. Balance recovery from unexpected trips was characterized by trunk flexion and first recovery step measures.

RESULTS

Recovery step length was smaller and maximum trunk flexion became larger in the mental fatigue group compared with those in the no fatigue group. Physical fatigue did not significantly affect trunk flexion and first recovery step measures.

CONCLUSION

Mental fatigue increased the likelihood of loss of balance. Thus, mental fatigue could be a risk factor for trips and falls. To prevent trip-related falls, interventions should be adopted to prevent prolonged exposures to cognitively demanding activities in occupational settings.

Effect of Mental Fatigue on Postural Sway in Healthy Older Adults and Stroke Populations

The aim of this study was to examine the effect of mental fatigue on postural sway under different sensory conditions in healthy older adults and in persons with chronic stroke (PwCS). Thirty healthy older adults (> 60 years old), randomly separated into experimental and control groups, as well as 15 PwCS participated in this study. Experimental groups were asked to stand on a force platform wearing seven inertial sensors while performing the Sensory Organization Test (SOT) under two cognitive conditions (single- and dual-task) before and after a mental fatigue task (stop-signal task for 60 min). The control group performed the same protocol before and after watching a movie for 60 min. Changes in subjective fatigue was assessed by the NASA Task Load Index and psychophysiological workload was assessed by heart rate variability (HRV). Postural sway was assessed by calculating the Jerk and root mean square (RMS) of center of mass (COM). Higher Jerk and RMS of COM (p < 0.05) were observed after the mental fatigue task in both healthy older adults and PwCS during SOT, which was not observed in the control group (p > 0.05). Additionally, postural sway increased in the three groups as the SOT conditions became more challenging. Our results indicate that mental fatigue, induced by sustained cognitive activity, can impair balance during SOT in older adult and stroke populations.

Nonlinear dynamics analysis of the human balance control subjected to physical and sensory perturbations

Postural control after applying perturbation involves neural and muscular efforts to limit the center of mass (CoM) motion. Linear dynamical approaches may not unveil all complexities of body efforts. This study was aimed at determining two nonlinear dynamics parameters (fractal dimension (FD) and largest Lyapunov exponent (LLE)) in addition to the linear standing metrics of balance in perturbed stance. Sixteen healthy young males were subjected to sudden rotations of the standing platform. The vision and cognition during the standing were also interfered. Motion capturing was used to measure the lower limb joints and the CoM displacements. The CoM path length as a linear parameter was increased by elimination of vision (p<0.01) and adding a cognitive load (p<0.01). The CoM nonlinear metric FD was decreased due to the cognitive loads (p<0.001). The visual interference increased the FD of all joints when the task included the cognitive loads (p<0.01). The slightly positive LLE values showed weakly-chaotic behavior of the whole body. The local joint rotations indicated higher LLEs. Results indicated weakly chaotic response of the whole body. Increase in the task difficulty by adding sensory interference had difference effects on parameters. Linear and nonlinear metrics of the perturbed stance showed that a combination of them may properly represent the body behavior.

Effects of visual and cognitive interference on joint contributions in perturbed standing: a temporal and spectral analysis

Postural balance requires using joint strategies which may be changed from normal conditions by interfering with the sensory information. The goal of the present study was to quantitatively evaluate the role of the joint mechanisms during perturbed stance. Visual and cognitive interference was imposed to sixteen healthy young males under rotational toes-down or up perturbations. Power spectral analysis was employed to distinguish the joint contribution and their in- or out-phase co-works. Results showed that addition of cognitive loads reduce the stability by increasing the center of mass (CoM) power to three times greater. Besides the CoM, the knee and hip powers were also significantly enhanced by the cognitive loads (p < .004), but the ankle was not influenced by cognition involvement (p > .05). Elimination of the vision had lower effect on the time and spectral functions of the knee and hip while the ankle rotations were increased due to the lack of visual feedback (p = .001). The toes-down perturbations resulted in more prominent contribution of the knee while the toes-up evoked the hip joint to keep the balance more than the other joints. Addition of the cognitive loads hindered the reactions of the joint mechanisms and vision caused more conservative responses of the joints.

Time-to-Boundary Function to Study the Development of Upright Stance Control in Children

Background:

The development of postural control across the primary school time horizon is a complex process, which entails biomechanics modifications, the maturation of cognitive ability and sensorimotor organization, and the emergence of anticipatory behaviour. Postural stability in upright stance has been thus object of a multiplicity of studies to better characterize postural control in this age span, with a variety of methodological approaches. The analysis of the Time-to-Boundary function (TtB), which specifies the spatiotemporal proximity of the Centre of Pressure (CoP) to the stability boundaries in the regulation of posture in upright stance, is among the techniques used to better characterize postural stability in adults, but, as of now, it has not yet been introduced in developmental studies. The aim of this study was thus to apply this technique to evaluate the development of postural control in a sample population of primary school children.

Methods:

In this cross-sectional study, upright stance trials under eyes open and eyes closed were administered to 107 healthy children, divided into three age groups (41 for Seven Years' Group, Y7; 38 for Nine Years' Group, Y9; 28 for Eleven Years' Group, Y11). CoP data were recorded to calculate the Time-to-Boundary function (TtB), from which four spatio-temporal parameters were extracted: the mean value and the standard deviation of TtB minima (M_min, Std_min), and the mean value and the standard deviation of the temporal distance between two successive minima (M_dist, Std_dist).

Results:

With eyes closed, M_min and Std_min significantly decreased and M_dist and Std_dist increased for the Y7 group, at Y9 M_min significantly decreased and Std_dist increased, while no effect of vision resulted for Y11. Regarding age groups, M_min was significantly higher for Y9 than Y7, and Std_min for Y9 was higher than both Y7 and Y11; M_dist and Std_dist resulted higher for Y11 than for Y9.

Conclusion:

From the combined results from the spatio-temporal TtB parameters, it is suggested that, at 9 years, children look more efficient in terms of exploring their limits of stability than at 7, and at 11 the observed TtB behaviour hints at the possibility that, at that age, they have almost completed the maturation of postural control in upright stance, also in terms of integration of the spatio-temporal information.

Influence of affective auditory stimuli on balance control during static stance

The main purpose of this study was to examine the effects of affective auditory stimuli on balance control during static stance. Twelve female and 12 male participants were recruited. Each participant completed four upright standing trials including three auditory stimuli trials and one baseline trial (ie no auditory stimuli). The three auditory stimuli trials corresponded to the pleasant, neutral and unpleasant sound conditions. Center of pressure (COP) measures were used to quantify balance control performance. It was found that unpleasant auditory stimuli were associated with larger COP amplitude in the AP direction compared to the rest testing conditions. There were no significant interaction effects between 'auditory stimuli' and gender. These findings suggested that some specificities presented by auditory stimuli are important for balance control, and the effects of auditory stimuli on balance control were dependent on their affective components. Practitioner Summary: Findings from this study can aid in better understanding of the relationship between auditory stimuli and balance control. In particular, unpleasant auditory stimuli were found to result in poorer balance control and higher fall risks. Therefore, to prevent fall accidents, interventions should be developed to reduce exposures to unpleasant sound.

Body sway adaptation to addition but not withdrawal of stabilizing visual information is delayed by a concurrent cognitive task

The aim of this study was to test the effects of a concurrent cognitive task on the promptness of the sensorimotor integration and reweighting processes following addition and withdrawal of vision. Fourteen subjects stood in tandem while vision was passively added and removed. Subjects performed a cognitive task, consisting of counting backward in steps of three, or were "mentally idle." We estimated the time intervals following addition and withdrawal of vision at which body sway began to change. We also estimated the time constant of the exponential change in body oscillation until the new level of sway was reached, consistent with the current visual state. Under the mentally idle condition, mean latency was 0.67 and 0.46 s and the mean time constant was 1.27 and 0.59 s for vision addition and withdrawal, respectively. Following addition of vision, counting backward delayed the latency by about 300 ms, without affecting the time constant. Following withdrawal, counting backward had no significant effect on either latency or time constant. The extension by counting backward of the time interval to stabilization onset on addition of vision suggests a competition for allocation of cortical resources. Conversely, the absence of cognitive task effect on the rapid onset of destabilization on vision withdrawal, and on the relevant reweighting time course, advocates the intervention of a subcortical process. Diverting attention from a challenging standing task discloses a cortical supervision on the process of sensorimotor integration of new balance-stabilizing information. A subcortical process would instead organize the response to removal of the stabilizing sensory input.NEW & NOTEWORTHY This study is the first to test the effect of an arithmetic task on the time course of balance readjustment following visual withdrawal or addition. Performing such a cognitive task increases the time delay following addition of vision but has no effect on withdrawal dynamics. This suggests that sensorimotor integration following addition of a stabilizing signal is performed at a cortical level, whereas the response to its withdrawal is "automatic" and accomplished at a subcortical level.

Effects of distractors on upright balance performance in school-aged children with attention deficit hyperactivity disorder, preliminary study

INTRODUCTION

Attention deficit hyperactivity disorder is a common impairing neuropsychiatric disorder with onset in early childhood. Almost half of the children with attention deficit hyperactivity disorder also experience a variety of motor-related dysfunctions ranging from fine/gross motor control problems to difficulties in maintaining balance.

OBJECTIVES

The main purpose of this study was to investigate the effects of distractors two different auditory distractors namely, relaxing music and white noise on upright balance performance in children with attention deficit hyperactivity disorder.

METHODS

We compared upright balance performance and the involvement of different sensory systems in the presence of auditory distractors between school-aged children with attention deficit hyperactivity disorder (n=26) and typically developing controls (n=20). Neurocom SMART Balance Master Dynamic Posturography device was used for the sensory organization test. Sensory organization test was repeated three times for each participant in three different test environments.

RESULTS

The balance scores in the silence environment were lower in the attention deficit hyperactivity disorder group but the differences were not statistically significant. In addition to lower balance scores the visual and vestibular ratios were also lower. Auditory distractors affected the general balance performance positively for both groups. More challenging conditions, using an unstable platform with distorted somatosensory signals were more affected. Relaxing music was more effective in the control group, and white noise was more effective in the attention deficit hyperactivity disorder group and the positive effects of white noise became more apparent in challenging conditions.

CONCLUSION

To the best of our knowledge, this is the first study evaluating balance performance in children with attention deficit hyperactivity disorder under the effects of auditory distractors. Although more studies are needed, our results indicate that auditory distractors may have enhancing effects on upright balance performance in children with attention deficit hyperactivity disorder.

Effect of Cognitive Load on Seating Posture in Children

Although children are frequently required to sit upright, it is often difficult to maintain this posture when performing cognitive tasks. Information about the relationship between a cognitive tasks and postural seating control is important for children to complete tasks more effectively. To determine the muscle activity and body sway of children in a seated posture while performing a cognitive task, changes in muscle activity and center of pressure (COP) were recorded while 4(th) grade children performed arithmetic tasks. Electromyography was recorded from the internal oblique and lumbar multifidus muscles, and the COP was recorded using a baropodometer placed on the stool. These variables were measured during easy (EA) and difficult (DA) arithmetic tasks. EMG activity decreased during the EA and DA tasks, while the COP was displaced in the DA task. The results of the arithmetic tasks were not related to the EMG or COP changes. Attention to maintain a seated posture may be reduced when children perform cognitive tasks. Therefore, it may be better to allow children to alter their posture especially when they are performing difficult tasks. In this research, we only used arithmetic tasks as the cognitive exercise, and therefore, other types of tasks should be examined.

Postural control in underachieving students

Postural balance is a sensory-motor function resulting from a learning process.

OBJECTIVE

To evaluate the postural control of underachieving students through static posturography together with virtual reality stimulation.

METHODS

This was a controlled cross-sectional study of a group of 51 underachieving students and a control group of 60 students with good school performance, with no history of vestibular disorders or neurotological complaints, volunteers from the community, age- and gender-matched. The students were submitted to Balance Rehabilitation Unit (BRU™) posturography.

RESULTS

A total of 111 students aged 7 to 12 years old were evaluated. At posturography evaluation, there was no significant difference between the limit of stability area (cm2) of the control group and the experimental group. The comparison between groups demonstrated a statistically significant difference (p < 0.05) in the values of sway velocity (cm/s) and center of pressure area (cm2) in the ten sensory conditions evaluated.

CONCLUSION

Posturography with virtual reality stimulation, allows for the identification of incapacity to maintain postural control, with or without visual deprivation, and the assessment of visual, somatosensory, and vestibular-visual interaction conflict in underachieving students.

Saccades improve postural control: a developmental study in normal children

INTRODUCTION

Dual-task performance is known to affect postural stability in children. This study focused on the effect of oculomotor tasks like saccadic eye movements on postural stability, studied in a large population of children by recording simultaneously their eye movements and posture.

MATERIALS AND METHODS

Ninety-five healthy children from 5.8 to 17.6 years old were examined. All children were free of any vestibular, neurological, ophtalmologic and orthoptic abnormalities. Postural control was measured with a force platform TechnoConcept®, and eye movements with video oculography (MobilEBT®). Children performed two oculomotor tasks: fixation of a stable central target and horizontal saccades. We measured the saccade latency and the number of saccades during fixation as well as the surface, length and mean velocity of the center of pressure.

RESULTS

During postural measurement, we observed a correlation between the age on the one hand and a decrease in saccade latency as well as an improvement in the quality of fixation on the other. Postural sway decreases with age and is reduced in the dual task (saccades) in comparison with a simple task of fixation.

DISCUSSION - CONCLUSION

These results suggest a maturation of neural circuits controlling posture and eye movements during childhood. This study also shows the presence of an interaction between the oculomotor system and the postural system. Engaging in oculomotor tasks results in a reduction of postural sway.

The effect of a Stroop-like task on postural control in dyslexic children

The influence of a secondary task on concurrent postural control was explored in twenty-one dyslexic children (mean age: 10.4 ± 0.3 years). Data were compared with twenty age-matched non-dyslexic children. As a secondary task, a modified Stroop test was used, in which words were replaced with pictures of fruits. The postural control of children was recorded in standard Romberg condition as the children were asked to name the colour of fruits appearing consecutively on a computer screen. Two conditions were tested: a congruent condition, in which the fruit was drawn in its natural ripe colour, and a non-congruent colour condition (NC), in which the fruit was drawn in three abnormal colours. A fixating condition was used as baseline. We analyzed the surface, length and mean speed of the center of pressure and measured the number of correct responses in the Stroop-like tasks. Dyslexic children were seen to be significantly more unstable than non-dyslexic ones. For both groups of children, the secondary task significantly increased postural instability in comparison with the fixating condition. The number of correct responses in the modified Stroop task was significantly higher in the non-dyslexic than in the dyslexic group. The postural instability observed in dyslexic children is in line with the cerebellar hypothesis and supports the idea of a deficit in automatic performance in such children. Furthermore, in accordance with cross domain competition model, our findings show that attentional resources are used to a greater extent by the secondary task than in controlling body stability.

Postural control among children with and without attention deficit hyperactivity disorder in single and dual conditions

Given the known deficits in attention in attention deficit hyperactivity disorder (ADHD) and the evidence suggesting that postural control requires attention, this study aimed to investigate the mechanisms of postural control of children with and without ADHD in single-(ST) and dual-task (DT) conditions. Postural sway and stabilogram diffusion analysis (SDA) were performed on the Center of Pressure trajectories on 24 ADHD children and 17 age-gender-matched healthy controls. The subjects were instructed to stand as stable as possible on a force platform in two task conditions: (1) single task (ST) and (2) dual task (DT)-an auditory-memory attention-demanding cognitive task. During ST and DT conditions, the ADHD children showed significantly greater ML-sway, short- and long-term effective diffusion coefficients, and critical displacement of SDA compared with controls. The effects of DT were somewhat unexpected; the control group indicated a significant decrease in ML-sway, AP-sway, sway area, and critical displacement of SDA; the ADHD group showed a significant decrease in ML-sway range and critical displacement. It is concluded that a greater sway displacement before closed-loop mechanisms is called into play in ADHD children. The DT enhanced balance control by reinforcing balance automaticity and minimizing sway in both healthy and ADHD children.

Effect of a dual task on postural control in dyslexic children

Several studies have examined postural control in dyslexic children; however, their results were inconclusive. This study investigated the effect of a dual task on postural stability in dyslexic children. Eighteen dyslexic children (mean age 10.3±1.2 years) were compared with eighteen non-dyslexic children of similar age. Postural stability was recorded with a platform (TechnoConcept®) while the child, in separate sessions, made reflex horizontal and vertical saccades of 10° of amplitude, and read a text silently. We measured the surface and the mean speed of the center of pressure (CoP). Reading performance was assessed by counting the number of words read during postural measures. Both groups of children were more stable while performing saccades than while reading a text. Furthermore, dyslexic children were significantly more unstable than non-dyslexic children, especially during the reading task. Finally, the number of words read by dyslexic children was significantly lower than that of non-dyslexic children and, in contrast to the non-dyslexic children. In line with the U-shaped non-linear interaction model, we suggest that the attention consumed by the reading task could be responsible for the loss of postural control in both groups of children. The postural instability observed in dyslexic children supports the hypothesis that such children have a lack of integration of multiple sensorimotor inputs.

A neurocognitive perspective on developmental disregard in children with hemiplegic cerebral palsy

A common problem in children with hemiplegic cerebral palsy (CP) is the asymmetrical development of arm and hand capacity caused by the lack of use of the affected upper limb, or developmental disregard. In this paper, we provide a neuropsychological model that relates developmental disregard to attentional processes and motor learning. From this model, we hypothesize that high attentional demands associated with the use of the affected upper limb might hinder its use in daily life, and therefore may be a factor in developmental disregard. This can be assessed with a dual-task paradigm. However, until now, this has not been applied to children with CP. We provide recommendations for using a dual-task paradigm in children with CP based on empirical studies in typically developing children and children with developmental coordination disorder. Ultimately, these dual-task studies may be used to improve interventions aimed at reducing developmental disregard.

Physical load handling and listening comprehension effects on balance control

The purpose of this study was to determine the physical load handling and listening comprehension effects on balance control. A total of 16 young and 16 elderly participants were recruited in this study. The physical load handling task required holding a 5-kg load in each hand with arms at sides. The listening comprehension task involved attentive listening to a short conversation. Three short questions were asked regarding the conversation right after the testing trial to test the participants' attentiveness during the experiment. Balance control was assessed by centre of pressure-based measures, which were calculated from the force platform data when the participants were quietly standing upright on a force platform. Results from this study showed that both physical load handling and listening comprehension adversely affected balance control. Physical load handling had a more deleterious effect on balance control under the listening comprehension condition vs. no-listening comprehension condition. Based on the findings from this study, interventions for the improvement of balance could be focused on avoiding exposures to physically demanding tasks and cognitively demanding tasks simultaneously. STATEMENT OF RELEVANCE: Findings from this study can aid in better understanding how humans maintain balance, especially when physical and cognitive loads are applied. Such information is useful for developing interventions to prevent fall incidents and injuries in occupational settings and daily activities.

Age-related differences in cognitive and postural dual-task performance

The present experiment assessed, in children aged 7-11 and in adults, whether postural control is affected by cognitive processes and vice versa. Using a dual-task, the level of difficulty of a Stroop task and bipedal quiet stance varied alternatively. We hypothesised that the interference between cognitive and postural tasks was non-linear during childhood with a so-called turning point around 8. Twenty-seven children 7- to 11-years-old and nine adults participated in the experiments. The postural task was executed in a semi-tandem Romberg position. Two cognitive conditions (congruent and non-congruent Stroop conditions) and two postural situations (with and without perturbed proprioceptive inputs) were presented simultaneously with the instruction to respond as correctly as possible while remaining as stable as possible. Results showed that, in the Vib condition, CoP mean velocity decreased with the increased cognitive complexity only in children aged 7. Moreover, the data showed a non-linear decrease in postural sway during childhood, whatever the level of complexity of the cognitive and/or postural tasks. CoP mean amplitude and mean velocity decreased between 7 and 8, and again between age 11 and adults. This study (1) confirmed that the interference between mental activity and postural control can be attributed mainly to attentional limitations, (2) showed the existence of a turning point around 8 in the development of this capacity, and (3) suggested that the mature level of attentional resources was not reached until age 11. Further research is needed to assess the development of attention implied in a cognitive/postural dual-task, including probably another so-called turning point during the adolescence.

Postural control and attentional demand during adolescence

In the present study we aimed to determine the attentional cost of postural control during adolescence by studying the influence of a cognitive task on concurrent postural control. 38 teenagers aged 12 to 17years and 13 young adults (mean age=26.1) stood barefoot on a force platform in a semi-tandem position. A dual-task paradigm consisted of performing a Stroop or a COUNTING BACKWARD task while simultaneously standing quietly on a firm or foam support surface. Different centre of pressure (CoP) measures were calculated (90% confidence ellipse area, mean velocity, root mean square on the antero-posterior (AP) and medio-lateral (ML) axes). The number and percentage of correct responses in the cognitive tasks were also recorded. Our results indicate (1) higher values of surface, ML mean velocity and ML RMS in the COUNTING BACKWARD task in adolescents aged 12 to 15 than in teenagers aged 16 to 17 and in adults, regardless of the complexity of the postural task and, (2) better cognitive performances in the Stroop than in the COUNTING BACKWARD task. The difference in the dual-task performance between the different age groups and particularly the existence of a turning point around 14-15years of age might be due to 1) difficulties in properly allocating attentional resources to two simultaneous tasks and/or, 2) the inability to manage increased cognitive requests because of a limited information processing capacity in adolescents aged 14-15years.

To freeze or not to freeze? Affective and cognitive perturbations have markedly different effects on postural control

Similar effects have been reported for diverting attention from postural control and increased anxiety on the characteristics of center-of-pressure (COP) time series (decreased excursions and elevated mean power frequency). These effects have also received similar interpretations in terms of increased postural stiffness, suggesting that cognitive and affective manipulations have similar influences on postural control. The present experiment tested this hypothesis by comparing postural conditions involving manipulations of attention (diverting attention from posture using cognitive and motor dual tasks) and anxiety (standing at a height), and by complementing posturography with electromyographic analyses to directly examine neuromuscular stiffness control. Affective and cognitive manipulations had markedly different effects. Unlike the height condition, diverting attention from balance induced smaller COP amplitudes and higher sway frequencies. In addition, more regular COP trajectories (lower sample entropy) were found in the height condition than the dual-task conditions, suggesting elevated attentional investment in posture under the affective manipulation. Finally, based on an analysis of the cross-correlation function between anterior-posterior COP time series and enveloped calf muscle activity, indications of tighter anticipatory neuromuscular control of posture were found for the height condition only. Our data suggest that affective and cognitive perturbations have qualitatively different effects on postural control, and thus are likely to be associated with different control processes, as evidenced by differences in neuromuscular regulation and attentional investment in posture.

Stability limits in the assessment of postural control through the Time-to-boundary function

The extraction of the Time-to-boundary function (TtB) from CoP data in upright stance trials has recently gained much attention. In this contribution, some parameters extracted from TtB in unperturbed upright stance trials were analysed in terms of variability with respect to different hypothesized stability limits. In particular, nonlinear stability factors were analyzed as a function of the different values for the boundary limits through which TtB is calculated. A sample population of 5 healthy young adults underwent upright stance trials in different conditions. The amplitude nonlinear stability factors showed a strong dependency with the boundary limits, which on the contrary did not affect the rhythmical nonlinear stability factors.