Memory coding in individuals with Down syndrome

Previous research has identified a deficit in phonological short-term memory in individuals with Down syndrome.

The present work aimed to analyze how a group of 30 individuals with Down syndrome performed in a picture span task compared with 30 typically developing children of the same mental age. The task involved four conditions (i.e., dissimilar, phonologically similar, visually similar, and long-name items) chosen to analyze the strategy used by individuals with Down syndrome to code visually presented nameable items.

Individuals with Down syndrome performed less well than typically developing children. Both groups showed the visual similarity effect.

Taken together, our results confirm that individuals with Down syndrome have a verbal working memory deficit, even when nameable items are presented visually. Mental age appears to be an important determinant of memory coding stage in individuals with Down syndrome.     

Effects of gait pattern and arm swing on intergirdle coordination

Mature locomotion in humans is characterized by an anti-phase coordination (moving in opposite directions) between the pelvic and the scapular girdles. This pattern involves a specific relationship between the arm and leg motion is deemed to be most flexible and dynamically efficient. Still, when the arms are involved in another task, like a field player running with a ball in the hands, locomotion is still possible. In order to probe the flexibility of the locomotor synergy, the present study aimed to determine the persistence and the strength of the coordination patterns between the pelvic and scapular girdles when no arm swing was allowed during walking and running. Relative phase, the time difference between the girdle rotations, measured the ongoing inter-girdle coordination of eight healthy participants asked to walk and run with or without arm swing. Results showed that an absence of arm swing led to a change from an anti-phase to in-phase pattern (girdles moving in the same direction) and that an increase in velocity strengthened the adopted pattern. Moreover, the frequency distribution of relative phase for all gait patterns with arm swing proved to be bimodal, indicating that the prevailing anti-phase pattern was always mixed with a noticeable proportion of in-phase coordination. The presence of the in-phase pattern in the easy, natural locomotion with arm swing manifests its persistence and its stability, perhaps pertaining to its prevalence in earlier times in ontogeny or evolution.     

Classification of gait muscle activation patterns according to knee injury history using a support vector machine approach

Abnormal muscle activation patterns during gait following knee injury that persist past the acute injury and rehabilitation phase (>three years) are not well characterized but may be related to post-traumatic knee osteoarthritis. The aim was to characterize the abnormal muscle activity from electromyograms of five leg muscles that were recorded during treadmill walking for young adults with and without a previous knee injury 3–12 years prior. The wavelet transformed and amplitude normalized electromyograms yielded intensity patterns that reflect the muscle activity of these muscles resolved in time and frequency. Patterns belonging to the affected or unaffected leg in previously injured participants and patterns belonging to a previously injured vs. uninjured participant were grouped and then classified using a principal component analysis followed by a support vector machine. A leave-one-out cross-validation was used to test the model significance and generalization. The results showed that trained classifiers could successfully recognize whether muscle activation patterns belonged to the affected or unaffected leg of previously injured individuals. Classification rates of 83% were obtained for all subjects, 100% for females only, indicating sex-specific knee injury effects. In contrast, it was not possible to discriminate between patterns belonging to the previously injured legs or dominant legs of control subjects. For females, the injured leg showed a stronger muscle activity for hamstring muscles and a lower activity for the vastus lateralis. In conclusion, systematic knee injury effects on the neuromuscular control of the knee during gait were present 3–12 years later.     

Spinal kinematics during gait in healthy individuals across different age groups

Most studies investigating trunk kinematics have not provided adequate quantification of spinal motion, resulting in a limited understanding of the healthy spine’s biomechanical behavior during gait. This study aimed at assessing spinal motion during gait in adolescents, adults and older individuals.Fourteen adolescents (10–18 years), 13 adults (19–35 years) and 15 older individuals (≥65 years) were included. Using a previously validated enhanced optical motion capture approach, sagittal and frontal plane spinal curvature angles and general trunk kinematics were measured during shod walking at a self-selected normal speed.Postural differences indicated that lumbar lordosis and thoracic kyphosis increase throughout adolescence and reach their peak in adulthood. The absence of excessive thoracic kyphosis in older individuals could be explained by a previously reported subdivision in those who develop excessive kyphosis and those who maintain their curve. Furthermore, adults displayed increased lumbar spine range of motion as compared to the adolescents, whereas the increased values in older individuals were found to be related to higher gait speeds. This dataset on the age-related kinematics of the healthy spine can serve as a basis for understanding pathological deviations and monitoring rehabilitation progression.     

Contralateral pelvic drop during gait increases knee adduction moments of asymptomatic individuals

PurposeThe current study purpose was to investigate the effects of contralateral pelvic drop gait on the magnitude of the knee adduction moment (KAM) within asymptomatic individuals.Methods15 participants walked on a dual belt instrumented treadmill while segment motions and ground reaction forces were recorded. Participants completed typical gait trials and pelvic drop gait trials. The net external KAM was calculated using inverse dynamics. Peak and impulse were identified. Frontal plane hip abduction/adduction and pelvic drop were determined. Correlations and paired t-tests were used for statistical hypothesis testing (alpha = 0.05).ResultsPeak hip adduction angle reached 4° (±6°) during pelvic drop trials compared to 0° (±6°) in the typical gait trials (p < 0.05) equating to 4° of pelvic drop. KAM impulse was higher in the pelvic drop trial (0.16 Nm s/kg ± 0.04) compared to the typical gait trial (0.13 Nm s/kg ± 0.05) (p < 0.001). Peak KAM was higher in the pelvic drop trial (0.55 Nm/kg ± 0.15) compared to the typical gait trial (0.40 Nm/kg ± 0.109) (p < 0.001). Correlations between change in KAM and change in hip adduction moment and pelvic drop were r > 0.80 (p < 0.001).ConclusionPelvic drop gait increased KAM peak and impulse. Results have implications for understanding relationships between frontal plane hip movement and the knee adduction moment during gait.     

Reliability of upper extremity kinematics while performing different tasks in individuals with stroke

Assessments of upper extremity performance typically include qualitative rather than quantitative measures of functional ability. Kinematic analysis is an objective, discriminative measure that quantifies movement biomechanics; however, the use within the poststroke impaired upper extremity is not well established. The purpose of this study was to examine the reliability of upper extremity kinematics in 18 individuals with stroke and 9 healthy controls. Participants performed reaching and grasping tasks over 2 separate days and metrics included movement time, peak velocity, index of curvature, trunk displacement, maximum aperture, and percentage of the movement cycle where maximum aperture occurred. The results showed moderate to high intraclass correlation and low standard error of measurement values for most variables, demonstrating that kinematic analysis may be a feasible and useful tool to quantify upper extremity movement after stroke.     

Action coordination in groups and individuals: learning anticipatory control

When individuals act alone, they can internally coordinate the actions at hand. Such coordination is not feasible when individuals act together in a group. The present research examines to what extent groups encounter specific challenges when acting jointly and whether these challenges impede extending planning into the future. Individuals and groups carried out a tracking task that required learning a new anticipatory control strategy. The results show that groups face additional demands that are harder to overcome when planning needs to be extended into the future. Information about others' actions is a necessary condition for groups to effectively learn to extend their plans. Possible mechanisms for exerting and learning anticipatory control are discussed.     

Comparison of gait patterns between young and elderly women: an examination of coordination

This study investigated intralimb coordination during walking in young and elderly women using the theoretical model of dynamical systems. 20 women, 10 Young (M age=24.6 yr., SD= 3.2 yr.) and 10 Elderly (M age=73.7 yr., SD=4.9 yr.), were videotaped during free speed gait and gait perturbed by an ankle weight. Two parameters, one describing the phasing relationship between segments (mean absolute relative phase) and the other the variability of this relationship (deviation in phase), were calculated from the kinematics. Two-way analysis of variance (age and weight) with repeated measures on weight indicated that during the braking period the weight increased the mean absolute relative phase between the shank and the thigh and decreased it between the foot and the shank. The Elderly women had significant smaller values for the mean absolute relative phase between the shank and the thigh during the braking period. For the same period, deviation in phase increased for the segmental 'relationship between the shank and the thigh. The findings suggest that changes in intralimb coordination take place with asymmetrical weighting and the aging process. These changes are most clearly present during the braking period.     

Enhanced arm swing alters interlimb coordination during overground walking in individuals with traumatic brain injury

The current study investigated interlimb coordination in individuals with traumatic brain injury (TBI) during overground walking. The study involved 10 participants with coordination, balance, and gait abnormalities post-TBI, as well as 10 sex- and age-matched healthy control individuals. Participants walked 12 m under two experimental conditions: 1) at self-selected comfortable walking speeds; and 2) with instructions to increase the amplitude and out-of-phase coordination of arm swinging. The gait was assessed with a set of spatiotemporal and kinematic parameters including the gait velocity, step length and width, double support time, lateral displacement of the center of mass, the amplitude of horizontal trunk rotation, and angular motions at shoulder and hip joints in sagittal plane. Interlimb coordination (coupling) was analyzed as the relative phase angles between the left and right shoulders, hips, and contralateral shoulders and hips, with an ideal out-of-phase coupling of 180° and ideal in-phase coupling of 0°. The TBI group showed much less interlimb coupling of the above pairs of joint motions than the control group. When participants were required to increase and synchronize arm swinging, coupling between shoulder and hip motions was significantly improved in both groups. Enhanced arm swinging was associated with greater hip and shoulder motion amplitudes, and greater step length. No other significant changes in spatiotemporal or kinematic gait characteristics were found in either group. The results suggest that arm swinging may be a gait parameter that, if controlled properly, can improve interlimb coordination during overground walking in patients with TBI.     

Grip and load force control and coordination in individuals with diabetes in different manipulation tasks

The study aimed to investigate the control and coordination of grip force (normal component) and load force (tangential component) in three different manipulation tasks in individuals with diabetes with and with no diagnosis of diabetic peripheral neuropathy (DPN) and healthy controls. Twenty-four individuals with type 2 diabetes mellitus, 12 with no (nDPN) and 12 with DPN (wDPN), and 12 healthy controls performed three manipulation tasks (static holding, lifting and holding, and oscillation) with the dominant hand, using an instrumented handle. Relative safety margin (% of GF exerted above the minimum GF needed to hold the object) was measured in all tasks. Individuals with diabetes from the nDPN and wDPN groups set lower relative safety margin than controls only in the static holding task. No other group effect was revealed, except a lower coefficient of friction between skin and object surface in individuals with DPN. The coordination between grip and load force and grip force control was not affected by the diabetes during dynamic manipulation tasks (lifting and holding and oscillation). However, when individuals with diabetes without and with DPN performed a manipulation task in which the inflow of cutaneous information was small and stable (static holding), grip force control was affected by the disease. This finding indicates that individuals with type 2 diabetes mellitus not diagnosed with DPN, already show mild impairments in the nervous system that could affect grip force control and that could be one of the first signs of neuropathy caused by the diabetes.     

The starting distance of obstacle circumvention did not affect intersegmental coordination in individuals with Parkinson's disease

BackgroundObstacle circumvention is a challenging task in Parkinson's disease (PD). Body segments adjustments, such as changing the direction of the trunk, followed by a change in the direction of the head, and modifications in the positioning of the feet, are necessary to circumvent an obstacle during walking. For that, individuals need to identify the distance to the obstacle, its characteristics (such as its dimension), and perform well-coordinated movements. However, PD is characterized by rigidity, which may be increased in the axial axis and compromise the task execution. Also, worsening sensory integration in PD may increase the time to perform these body segments adjustments, thus impairing the movement coordination when starting obstacle circumvention near to the obstacle.AimTo determine if the starting distance (1.5 m, 3 m, or 5 m) from the obstacle could modify the intersegmental coordination (specifically, the coordination between head, trunk, and pelvis) during the obstacle circumvention steps in individuals with PD.MethodsFourteen individuals with a diagnosis of idiopathic PD and 15 neurologically healthy individuals (CG) from the community were included in this study. The participants were evaluated in three different gait conditions, according to the starting distance from the obstacle: 1.5 m, 3 m, and 5 m away from the obstacle. Vector coding technique was employed to establish the coupling between head, trunk, and pelvis in the steps immediately before and during obstacle circumvention. Three-way ANOVA's (group, distance, and step) were calculated with the level of significance at p < 0.05.ResultsFor all couplings of coordination, there were no effects of distance. However, significant main effects of group and steps (p < 0.05) were found for all couplings with different patterns of coordination: head/pelvis (group: in-phase and anti-phase variables; steps: anti-phase variable), head/trunk (group: trunk variable; steps: in-phase and anti-phase variables) and trunk/pelvis (group: anti-phase; steps: trunk and pelvis). Finally, only head/trunk coupling showed an interaction between group*steps. Individuals with PD showed 7.95% lower head movement (p < 0.024) and 14.85% greater trunk movement than CG (p < 0.002). Also, individuals with PD performed 17.56% greater head movement in the step before the circumvention compared to the step during circumvention (p < 0.044).ConclusionThe starting distance from the obstacle did not influence the pattern of axial intersegmental coordination in both groups. However, how these segments interact in the preparation and during the obstacle circumvention are opposite in individuals with PD. While on the previous step to obstacle circumvention, the head movement was greater than the trunk, during the obstacle circumvention step, individuals with PD rotated the trunk more.     

Errors in the ankle plantarflexor force production are related to the gait deficits of individuals with multiple sclerosis

BackgroundIndividuals with multiple sclerosis (MS) often have limited mobility that is thought to be due to the neuromuscular impairments of the ankle. Greater isometric motor control of the ankle has been associated with better standing postural balance but its relationship to mobility is less understood. The objectives of this investigation were to quantify the motor control of the ankle plantarflexors of individuals with MS during a dynamic isometric motor task, and explore the relationship between the ankle force control and gait alterations.MethodsFifteen individuals with MS and 15 healthy adults participated in both a dynamic isometric ankle plantarflexion force matching task and a biomechanical gait analysis.FindingsOur results displayed that the subjects with MS had a greater amount of error in their dynamic isometric force production, were weaker, walked with altered spatiotemporal kinematics, and had reduced maximal ankle moment at toe-off than the control group. The greater amount of error in the dynamic force production was related to the decreases in strength, step length, walking velocity, and maximal ankle moment during walking.InterpretationAltogether these results imply that errors in the ankle plantarflexion force production may be a limiting factor in the mobility of individuals with MS.     

Support vector machine for classification of walking conditions of persons after stroke with dropped foot

Walking with dropped foot represents a major gait disorder, which is observed in hemiparetic persons after stroke. This study explores the use of support vector machine (SVMs) to classify different walking conditions for hemiparetic subjects. Seven participants with dropped foot (category 4 of functional ambulatory category) walked in five different conditions: level ground, stair ascent, stair descent, upslope, and downslope. The kinematic data were measured by two portable sensor units, each comprising an accelerometer and gyroscope attached to the lower limb on the shank and foot segments. The overall classification accuracy of stair ascent, stair descent, and other walking conditions was 92.9% using input features from the sensor attached to the shank. It was further improved to 97.5% by adding two more inputs from the sensor attached to the foot. Stair ascent was also classified by the inputs from the foot sensor unit with 96% accuracy. The performance of an SVM was shown to be superior to that of other machine learning methods using artificial neural networks (ANN) and radial basis function neural networks (RBF). The results suggested that the SVM classification method could be applied as a tool for pathological gait analysis, pattern recognition, control signals in functional electrical stimulation (FES) and rehabilitation robot, as well as activity monitoring during rehabilitation of daily activities.     

Minimal detectable change of kinematic and spatiotemporal parameters in patients with chronic stroke across three sessions of gait analysis

Three-dimensional gait analysis is the gold standard for gait-assessment in patients with stroke. This technique is commonly used to assess the effect of treatment on gait parameters. In clinical practice, three gait analyses are usually carried out (baseline, after treatment and follow-up), the objectives were to define the reproducibility and the Minimum Detectable Change (MDC) for gait parameters in stance and swing measured using 3D-gait analysis, and to assess changes in MDC across three repeated 3D-gait analyses. Three gait analyses (V1, V2 and V3) were performed at 7-day intervals in twenty-six patients with chronic stroke. Kinematic data (in the sagittal plane, during swing and stance) and spatiotemporal data were evaluated for the paretic limb. Reliability was tested using repeated measures ANOVA with a Tukey post hoc test, and the MDC values were calculated for each parameter. Only the range of hip motion during swing changed significantly between V1 and V2, but no other kinematic parameters changed. No significant differences were observed for the spatiotemporal parameters. MDC values were always higher during the V1vsV2 comparison for both kinematic and spatiotemporal parameters. This is the first study to evaluate the MDC for kinematic and spatiotemporal parameters during stance and swing. Reliability of kinematic and spatiotemporal data across sessions was very good over the three sessions. MDC values were the lowest between V2 and V3 for most parameters. Use of the MDC will allow clinicians to more accurately determine the effect of treatments.     

Ipsilesional arm reaching movements are not affected by the postural configuration adopted by individuals with stroke

Individuals with stroke present several impairments in the ipsilesional arm reaching movements that can limit the execution of daily living activities. These impairments depend on the side of the brain lesion. The present study aimed to compare the arm reaching movements performed in sitting and standing positions and to examine whether the effects of the adopted posture configuration depend on the side of the brain lesion. Twenty right-handed individuals with stroke (half with right hemiparesis and a half with left hemiparesis) and twenty healthy adults (half used the left arm) reached toward a target displayed on a monitor screen placed in one of three heights (i.e., upper, central, or lower targets). Participants performed the reaches in sitting and standing positions under conditions where the target location was either well-known in advance (certainty condition) or unknown until the movement onset (uncertainty condition). The values of movement onset time, movement time, and constant error were compared across conditions (posture configuration and uncertainty) and groups for each target height. Individuals with stroke were slower and spent more time to start to move than healthy participants, mainly when they reached the superior target in the upright position and under the uncertainty condition. Individuals who have suffered a right stroke were more affected by the task conditions and those who suffered a left stroke showed less accurate reaches. Overall, these results were observed regardless of the adopted posture. The current findings suggested that ipsilesional arm reaching movements are not affected by the postural configuration adopted by individuals with stroke. The central nervous system modulates the reaching movements according to the target position, adopted posture, and the uncertainty in the final target position to be reached.     

Three-dimensional kinematics of the scapula and trunk,and associated scapular muscle timing in individuals with stroke

Poor scapulothoracic control is a risk for developing shoulder pathology, but has received little attention so far in individuals with stroke (IwS). Trunk and scapular kinematics and surface muscle activity were measured in 15 healthy controls and 18 IwS during a low and high forward flexion (FF). Group-differences in trunk and scapular kinematics were assessed during low and high FF using a t-test (independent samples). Differences in muscle onset and offset time relative to movement start (both FF tasks) were determined using a mixed model taking into account the different groups and muscles. Recruitment patterns per group and task were described based on significant differences between muscles. In IwS, earlier lower trapezius and late infraspinatus offset were found during low FF, as well as a later onset and earlier offset of serratus anterior. For low FF, significantly more trunk axial rotation was found in IwS during both elevation and lowering. During high FF, IwS showed significantly less scapular posterior tilt during elevation and more scapular lateral rotation during lowering. IwS demonstrated adaptive muscle timing with earlier initiation and late inactivation of lower trapezius and infraspinatus, possibly to compensate for a late activation and early deactivation of the serratus anterior and to establish as such the correct pattern of scapulothoracic movement.     

An examination of hypervigilance for external threat in individuals with generalized anxiety disorder and individuals with persecutory delusions using visual scan paths

One account of generalized anxiety disorder (GAD) is that it results from hypervigilance, manifest as excessive scanning of the external environment and preferential attention to threat. However, for individuals with GAD, there has been no direct study of scanning, and evidence for preferential attention to threat has only been found for threat-words. We therefore devised a new measure of hypervigilance. Visual scan paths were recorded of individuals with GAD (N=12) and people without a psychiatric illness (N=12) viewing complex pictures that varied in threat content. People with persecutory beliefs (N=11) also participated in the study to test the hypothesis that anxiety, via such hypervigilant cognitive processes, may contribute to the maintenance of delusions. Compared with the control group, the anxious individuals were not found either to scan excessively for or to look at threat. The anxiety group was therefore not hypervigilant for external threat, which is inconsistent with the hypervigilance model. As a consequence, the hypothesis that anxiety maintains delusions was not tested. However, additional support was found for the hypothesis that people with delusions form rapid judgements on the basis of less data-gathering than control groups who are either anxious or have no psychiatric illness.     

Evidence for generalized motor programs using gait pattern analysis

Human intra limb gait kinematics were analyzed via statistical and structural pattern recognition methods to determine the role of relative timing of limb segments within and between modes of gait. Five experienced runners were filmed while walking (3-6 km/hour) and running (8-12 km/hour) on a motor driven treadmill. Kinematic data consisted of relative timing of the four phases of the Philippson step cycle and intersegmental limb trajectories, determined from angle-angle diagrams. Despite marked decreases in absolute time durations within gaits remained constant over the speeds which were studied. Although a 2-fold increase in locomotor speed occurred in walking and a 1.5-fold speed increase occurred within running, the percentage of time spent in each of the Philippson phases was not significantly changed. However, significant differences in the time percentages and sequences of the step cycle phases were found between walking and running. Correlations between limb segment trajectories occurring in the different gaits showed strong coherence for overall step cycle patterns, but within step cycle phases and across speeds, selective phases displayed little correspondence.     

Color coding information: assessing alternative coding systems using independent brightness and hue dimensions

Can independent dimensions of brightness and hue be used in a combined digital information code? This issue was addressed by developing 2 color-coding systems and testing them on informed and naive participants in signal beam detection and classification experiments for simulated sonar displays. Each coding system's results showed both groups efficiently used encoded information that varied simultaneously along the 2 dimensions of brightness and hue. Findings support the proposed procedures for developing color information codes and the validity of such information codes across different populations. Applied significance of these results is provided by the test of principled methods of color-code construction and the demonstration that extending the information content of user interfaces beyond 1 dimension is feasible in practice.