Biomedical subjects

Christina Schmitz

Publications and source records attributed to Christina Schmitz.

8 recordsLinked to original sources

PubMed2005

Development of postural control in healthy children: a functional approach.

From a set of experimental studies showing how intersegmental coordination develops during childhood in various posturokinetic tasks, we have established a repertoire of equilibrium strategies in the course of ontogenesis. The experimental data demonstrate that the first reference frame used for the organization of balance control during locomotion is the pelvis, especially in young children. Head stabilization during posturokinetic activities, particularly locomotion, constitutes a complex motor skill requiring a long time to develop during childhood. When studying the emergence of postural strategies, it is essential to distinguish between results that can be explained by biomechanical reasons strictly and those reflecting the maturation of the central nervous system (CNS). To address this problem, we have studied our young subjects in situations requiring various types of adaptation. The studies dealing with adaptation of postural strategies aimed at testing short and long-term adaptation capacity of the CNS during imposed transient external biomechanical constraints in healthy children, and during chronic internal constraints in children with skeletal pathologies. In addition to maintenance of balance, another function of posture is to ensure the orientation of a body segment. It appears that the control of orientation and the control of balance both require the trunk as an initial reference frame involving a development from egocentric to exocentric postural control. It is concluded that the first step for children consists in building a repertoire of postural strategies, and the second step consists in learning to select the most appropriate postural strategy, depending on the ability to anticipate the consequence of the movement in order to maintain balance control and the efficiency of the task.

Adaptation, Physiological↗

PubMed2005

From egocentric to exocentric spatial orientation: development of posture control in bimanual and trunk inclination tasks.

The authors investigated the emergence of independent control of body segments in bimanual tasks involving either voluntary or involuntary trunk motion by tracking the transition from an ego- to an exocentric mode of postural control during childhood (i.e., from body-referenced orientation to externally referenced action). A paradigm combining a seated manual task and various trunk manipulations described the coordination strategies used by 24 children at different ages (2 to 9 years) and by adults. The following questions were asked: (a) When do children begin to dissociate upper limb movements from those of the trunk? (b) What segmental strategies are exhibited by each age group (2-3, 4-6, and 7-9 years, and adults)? Kinematic analyses revealed that younger children (2-6 years) used either the trunk or the support surface as reference to orient the limbs. Older children (7-9 years) began to use a gravitational reference frame similar to that of adults; they uncoupled upper limb motion from the trunk in either voluntary or imposed conditions. Young children patterned the forearm trajectory after the initiating segment (support surface or the trunk), thus reducing the degrees of freedom during the dual task. Echoing previous reports, 7-9 years of age appears to be a critical period in which children master postural control and develop an internal representation of body scheme.

Adult↗

PubMed2004

Brain activity during predictable and unpredictable weight changes when lifting objects.

When humans repetitively lift the same object, the fingertip forces are targeted to the weight of the object. The anticipatory programming of the forces depends on sensorimotor memory representations that provide information on the object weight. In the present study, we investigate the neural substrates of these sensorimotor memory systems by recording the neural activity during predictable or unpredictable changes in the weight of an object in a lifting task. An unpredictable change in weight leads to erroneous programming of the fingertip forces. This triggers corrective mechanisms and an update of the sensorimotor memories. In the present fMRI study, healthy right-handed subjects repetitively lifted an object between right index finger and thumb. In the constant condition, which served as a control, the weight of the object remained constant (either 230 or 830 g). The weight alternated between 230 and 830 g during the regular condition and was irregularly changed between the two weights during the irregular condition. When we contrasted regular minus constant and irregular minus constant, we found activations in the right inferior frontal gyrus pars opercularis (area 44), the left parietal operculum and the right supramarginal gyrus. Furthermore, irregular was associated with stronger activation in the right inferior frontal cortex as compared with regular. Taken together, these results suggest that the updating of sensorimotor memory representations and the corrective reactions that occur when we manipulate different objects correspond to changes in synaptic activity in these fronto-parietal circuits.

Adult↗

PubMed2004

Impairment of a cortical event-related desynchronisation during a bimanual load-lifting task in children with autistic disorder.

In autism, the abilities of communication are affected, associated with abnormalities of cognitive, sensorial and motor development. In a previous study based on a load-lifting task, we showed impairment of anticipation in children with autism as evidenced by kinematics and eletromyographic recordings [Neurosci. Lett. 348 (2003) 17]. In the present study, we assessed the cortical counterparts of the use of anticipatory postural adjustments in a group of control children and in a group of children with autism. The tasks required maintaining a stable forearm position despite imposed or voluntary lifting of an object placed either on the controlateral forearm or on a support. We investigated the differences between the two groups of children on the Event-Related Desynchronisation (ERD) which precedes movement onset in adults [Electroencephalogr. Clin. Neurophysiol. 46 (1979) 138]. Electroencephalogram (EEG) power evolution of a 6-8-Hz frequency band was averaged before and after imposed or voluntary movement onset. EEG reactivity of control and autistic children did not differ during the imposed unloading condition, but significant differences appeared in the voluntary unloading situations. Before lifting the object, control children showed an ERD above the left motor areas. An ERD also occurred above the right motor areas when the object was placed on their forearm. This indicates that the ERD can also translate the use of anticipatory postural adjustments. By contrast, children with autism did not show an ERD in the two voluntary situations. This suggests a central deficit of anticipation in both postural and motor control in children with autism.

Autistic Disorder↗

PubMed2004

Effects of passive-active movement training on upper limb motor function and cortical activation in chronic patients with stroke: a pilot study.

OBJECTIVE: To explore how repetitive passive-active movement training effects upper limb motor function and cortical activation in patients with stroke. DESIGN: Single-group treatment trial with baseline comparisons. PATIENTS: Ten chronic patients with stroke with paresis of the upper limb. METHODS: Assessments were performed during a 4-week baseline period before and once after 4 weeks of training using the Motor Assessment Scale of the upper limb, Nine Hole Peg Test, goniometer for range of movement and the modified Ashworth scale for muscle tone. Two patients underwent functional magnetic resonance imaging pre- and post-training. The treatment consisted of daily sessions of repeated functional reaching and grasping movements guided passively and attempted actively during 4 weeks. RESULTS: The group improved in range of motion and Motor Assessment Scale scores. Subjects reported improvements in a variety of daily tasks requiring the use of the affected upper limb. Increases in cortical activation in prefrontal and sensorimotor areas were observed in parallel with improvements of upper limb motor function in the 2 patients scanned. CONCLUSION: The 4-week training programme improved hand motor function and ability. Cortical activation on functional magnetic resonance imaging changed in parallel suggesting reorganization of areas related to movements of the paretic limb.

Cerebral Cortex↗

PubMed2003

Motor control and children with autism: deficit of anticipatory function?

This study aims at investigating how do anticipatory postural adjustments develop in children with autism, during a bimanual load-lifting task that required maintaining the stabilisation of the forearm despite imposed or voluntary unloading. Elbow angle and electromyographic were recorded on the child forearm supporting the load. The forearm stabilisation was as good in children with autism as in the control group. However, in children with autism, the latencies for both kinematics and muscular events indicated an increase of the duration of unloading. These results indicate the use of a feedback rather than a feed-forward mode of control. Impairments in both the building of internal representations and the mastering of timing parameters, could explain the deficient postural anticipation reported in children with autism.

Autistic Disorder↗

PubMed2002

Developmental sequence in the acquisition of anticipation during a new co-ordination in a bimanual load-lifting task in children.

The aim of this experiment was to test the capacity of children to develop anticipation at various stages of their growth. We studied the learning process of an artificial co-ordination by means of a procedure of double unloading in two groups of children, and a group of adults. Elbow-joint angle measurement was used to assess for the improvement of the forearm stabilization through the six learning sessions. The main results report a developmental sequence of the acquisition of anticipatory postural adjustments (APA) similar to the one established for the ontogenesis of APA. A difference in learning dynamics, but also in the final level of performance, is reported between children aged 5-6 and children aged 7-8 years. The improvement occurring at the age of 7 years probably indicates maturation of internal representations, favourable to the faster setting up of operational anticipated control.

Adult↗

PubMed2001

Building anticipatory postural adjustment during childhood: a kinematic and electromyographic analysis of unloading in children from 4 to 8 years of age.

The present study addressed the question of how do anticipatory postural adjustments (APA) develop during childhood, in the range from 4 to 8 years, during a bimanual load-lifting task. This task required maintaining the stabilisation of the forearm position despite imposed or voluntary unloading of the forearm. Elbow angle and multiple surface EMG were recorded on the child postural forearm supporting a load. During voluntary unloading, the elbow flexion of the postural forearm was calculated as a percentage of the elbow flexion measured during the imposed situation. Improvement of the forearm stabilisation was observed mainly between 4--6 and 7--8 years of age, but the oldest children did not reach the adult level of stabilisation of the postural forearm. Moreover, a clear developmental sequence in the acquisition of APA was reported: first the selection of an efficient EMG pattern underlying the forearm stabilisation, and second the mastering of timing adjustments. In fact, regression of the co-contraction pattern was observed with age, together with selection of the adult-like reciprocal pattern. Mastering of the timing adjustments of the reciprocal pattern, characterised in adults by a well-synchronised co-ordination between onset of the flexor muscle contraction of the manual arm and onset of the flexor muscle inhibition of the postural forearm, progressively improves during development. Moreover, these results suggest that the internal representation of the consequences of unloading on the forearm stabilisation, underlying anticipatory function during a bimanual co-ordination task, slowly build up during childhood.

Adult↗