Gaze behaviour during interception in children with spastic unilateral cerebral palsy.

Anticipatory gaze behaviour during interceptive movements was investigated in children with Spastic Unilateral Cerebral Palsy (SUCP), and related to the side of the intracerebral lesion. Five children with lesions of the right hemisphere (RHL) and five children with lesions of the left hemisphere (LHL) had to walk towards and intercept a ball that moved perpendicular to the walking path. Interception accuracy and gaze patterns were measured in a no-occlusion and occlusion condition, in which the ball was occluded from view for half of its trajectory. There was a clear support for a relationship between gaze behaviour and success in interception performance, with some evidence for the presence of anticipatory gaze behaviour. There were also differences in gaze behaviour between children with RHL and children with LHL that might be related to planning, but these did not affect interception accuracy. It is concluded that gaze behaviour during interceptive movements is anticipatory, and at least partly dependent on the lesional side.

Visual guidance of interceptive actions in children with spastic unilateral cerebral palsy is influenced by the side of the lesion.

PURPOSE: To determine the type of visual information used by children with spastic unilateral cerebral palsy (SUCP) in order to intercept a ball and to verify whether this information was dependent on the side of the lesion. More specifically, it was examined whether the interception was controlled on the basis of a time or a distance strategy, initiating the catch when the ball is at a fixed time interval or at a fixed distance from the point of interception. METHODS: Three groups of children were included. Children with either a left sided (LHL) or a right sided lesion (RHL) and children without a lesion [typically developing (TD)] intercepted a ball from a conveyor belt. In order to intercept the ball successfully they had to walk and to reach for the ball at the interception point 4 m away. RESULTS: Children with LHL had a longer decision time and started their reach movement earlier. In 56% of the children with LHL a distance strategy was observed, while in the TD and the children with RHL predominantly a time strategy was found. CONCLUSIONS: The side of the lesion influences the visual information used to initiate interceptive actions.

Visual guidance during an interception task in children with Spastic Hemiparetic Cerebral Palsy.

The aims of the study are to determine the presence of adjustments in walking behaviour of children with Spastic Hemiparetic Cerebral Palsy (SHCP) during the interception of a moving ball and, whether the angle between the ball and the participant is kept constant. This would support the use of the so-called bearing angle (BA) strategy in interception of the object. Children with left hemisphere damage intercepted a ball from a conveyor belt at three different velocities, from a frontal or lateral orientation and with their impaired or less-impaired hand. The participants walked from a distance of 4m perpendicularly to the belt. Children seemed to have less successful trials when grasping with the impaired hand. The results showed that the walking velocity was adjusted to the ball velocity. When they grasped with the impaired hand, children initially moved faster to the interception point, while closer to the belt significant slower. The BA showed less variation over the trajectory when the children grasped with their less-impaired hand or when the ball velocity increased. It was concluded that children with SHCP were able to take their impairment into account as indicated by adjustments in walking behaviour. However, these adjustments in walking velocity were not sufficient to compensate totally for the limited reaching ability in the impaired hand. As a result of these adjustments, the amount of variation from the constant BA seemed to deviate more from typically developing children when grasping with impaired hand than when grasping with less-impaired hand.

Suppression of EMG activity by transcranial magnetic stimulation in human subjects during walking.

1. The involvement of the motor cortex during human walking was evaluated using transcranial magnetic stimulation (TMS) of the motor cortex at a variety of intensities. Recordings of EMG activity in tibialis anterior (TA) and soleus muscles during walking were rectified and averaged. 2. TMS of low intensity (below threshold for a motor-evoked potential, MEP) produced a suppression of ongoing EMG activity during walking. The average latency for this suppression was 40.0 +/- 1.0 ms. At slightly higher intensities of stimulation there was a facilitation of the EMG activity with an average latency of 29.5 +/- 1.0 ms. As the intensity of the stimulation was increased the facilitation increased in size and eventually a MEP was clear in individual sweeps. 3. In three subjects TMS was replaced by electrical stimulation over the motor cortex. Just below MEP threshold there was a clear facilitation at short latency (approximately 28 ms). As the intensity of the electrical stimulation was reduced the size of the facilitation decreased until it eventually disappeared. We did not observe a suppression of the EMG activity similar to that produced by TMS in any of the subjects. 4. The present study demonstrates that motoneuronal activity during walking can be suppressed by activation of intracortical inhibitory circuits. This illustrates for the first time that activity in the motor cortex is directly involved in the control of the muscles during human walking.

Acquisition of upper body stability during walking in toddlers.

This study examines the development of head and trunk movements in toddlers as they begin to walk independently. The data are from a longitudinal study of 7 infants observed from the onset of walking over a period of 46-80 weeks. Head and trunk rotations were measured in the frontal and sagittal planes together with global gait parameters (progression velocity, step cadence, length and width, duration of double support phase). The results showed that during the first weeks of walking head and trunk oscillations significantly decreased, indicating that considerable progress is made in upper body stabilization. Dramatic changes in global gait parameters also occurred at this time. After this first period of rapid changes, gait parameters continued the same developmental trend but with slower changes. The close relation between gain in head and trunk stability and improvement in walking efficacy is discussed on the basis of the individual developmental trends.

The build-up of anticipatory behaviour. An analysis of the development of gait initiation in children.

This study analyses the anticipatory postural adjustments during the gait initiation process in children aged 2.5, 4, 6 and 8 years. In adults, anticipation during gait initiation includes a shift in the centre of foot pressure (CP) both backwards and towards the stepping foot. Backward displacement and the duration of the anticipation phase covary with the gait progression velocity reached by the subject at the end of the first step. In the present study, the children walked on a force plate that allowed us to calculate the acceleration of the centre of mass and the displacements of the CP. The results showed three main characteristics of the development of anticipatory behaviour: (1) The occurrence of anticipatory displacements of the CP increased progressively with age. Systematic backward anticipation was found for all children except one of the youngest, whereas the lateral displacement was systematically observed later, in the 6-year group; (2) the amplitude of the spatial parameters showed a significant increase with age; (3) contrary to the adult, the amplitude of the backward shift did not covary with the forthcoming velocity in the youngest groups. This covariation became significant at 6 years and remained significant at 8 years. The results showed that even if anticipatory behaviour was present in 2.5-year-old children it is only later that the child is able of more accurate tuning of feedforward control, probably due to better control of the overall postural adjustments.

Head coordination as a means to assist sensory integration in learning to walk.

After a brief presentation of the development of free walking interpreted as learning dynamical equilibrium, the problem of sensory integration in the process of walking development is discussed. A critical review of the role of vision in the development of posturo-locomotor task is presented, along with recent test results on the development of the vestibular system. A final section presents the development of head stabilization and coordination as a necessary means to assist sensory integration. It is suggested that if sensory information is necessary to enhance posturo-locomotor skills, a good mastery of walking is in turn necessary to increase the efficiency of sensory integration.

Head coordination in the sagittal plane in toddlers during walking: preliminary results.

In adults, head rotations in the pitch plane are highly synchronized with vertical head translations during different locomotor tasks as walking, running, and hopping. The head is rotating up then down in the pitch plane as stepping movement drives the head down then up, respectively. The purpose of our study was to determine at which period of the motor control development this fine head coordination occurred. The organization of head movements was analyzed in four normal children observed longitudinally from the onset of walking up to 80 weeks of independent walking (IW). The degree of synchronization between vertical head translations and head rotations in the pitch plane was used to define an index of head coordination for 15 to 25 steps per child per session. Our results show that the coordination of head rotations in the pitch plane improves continually in toddlers but does not reach the optimal level during the first year of IW experience. We showed previously that head stabilization in space was achieved during the first weeks of IW. Both head stabilization in space and fine head coordination during walking are considered as directly involved in gaze stabilization, but in toddlers head stabilization in space is completed earlier than head coordination. Head stabilization appears to be a necessary motor control to acquire prior to the development of head movement coordination.

Trunk and head stabilization during the first months of independent walking.

This study measured the rate of acquisition of head and trunk postural control during the two early developmental periods of independent walking, as defined by global gait parameters. Gait parameters were observed longitudinally in four children. The maximum angular deviations of the trunk and head oscillations were computed in the frontal and sagittal planes. These decreased most dramatically during the first 10-15 weeks of independent walking, during the same period when global gait parameters changed rapidly. This head and trunk stabilization may be a fundamental process that help to maintain equilibrium during walking, and may be a necessary step prior to the development of fine posturo-motor control.