Biomedical subjects

J Vaal

Publications and source records attributed to J Vaal.

3 recordsLinked to original sources

PubMed2000

Spontaneous kicking behavior in infants: age-related effects of unilateral weighting.

The age-related effects of unilateral weighting on spontaneously generated kicks in 18 healthy, full-term infants were investigated. The main question was whether infants during the first half-year after birth reveal changes in how they adjust to unilateral weighting. At 6 weeks, infants reduced the frequency of the weighted leg and increased that of the unweighted leg whereas at 12 weeks the frequency of kicking increased in both legs. At both ages, unilateral weighting also resulted in differences on a number of kinematic parameters. By 18 and 26 weeks, such frequency and kinematic effects were no longer present. With regard to interlimb couplings, a clear pattern of bilateral coordination was only present at 26 weeks; these results suggest that the effects of unilateral weighting are not directly related to the tightness of interlimb couplings. The implications of these age-related differences for understanding developmental changes in the control of leg movements are discussed. It is suggested that the infants' improved ability to act in a task-specific manner as well as nonlinear changes in the musculo-skeletal system and fine-tuning processes at a neural level might be factors of importance.

Age Factors↗

PubMed2000

Development of spontaneous leg movements in infants with and without periventricular leukomalacia.

The main question asked in the present study was whether support could be found for the notion that supraspinal influences on the generation of spontaneous kicking movements become increasingly apparent in the first half-year after birth. In comparing groups of infants with and without damage in tracts connected with the cortex surrounding the central sulcus, such support would consist of the finding that similar patterns of spontaneous kicking are observed early in development, whereas differences between groups should occur with increasing age. Using 3-D registrations, the spontaneous kicking movements of 19 infants with differing degrees of periventricular, lobar, and subcortical leukomalacia based on white matter (WM) abnormalities on ultrasound were compared to those of 10 healthy control infants at 6, 12, 18, and 26 weeks of corrected age. Magnetic resonance imaging recordings were used to identify the location and severity of the brain lesions. Infants with extensive lesions in the periventricular and lobar WM with or without diffuse lesions in the subcortical WM showed a decreased variability on some spatial and temporal parameters of kicks. More importantly, these infants showed a different developmental course for intralimb couplings when compared to the other infants; they were unable to dissociate tight intralimb couplings at 18 and 26 weeks. As all of these infants had substantial damage of the corticospinal tracts, these findings suggest that these tracts are involved in the regulation of intralimb joint dissociations between 4 and 6 months of age. However, caution is needed as areas outside those in which the corticospinal tracts are located could be damaged as well and most of the infants with moderate to severe lesions in the corticospinal tract had additional psychomotor problems. For interlimb couplings and most of the spatial and temporal parameters of kicks, no differences were found between groups. This strengthens the claim that inter- and intralimb couplings are organized in fundamentally different ways.

Analysis of Variance↗

PubMed1994

Callosal size in children with learning disabilities.

The corpus callosum (CC), the main structure subserving hemispheric collaboration, that is necessary for efficient cognitive functioning, undergoes developmental processes such as axonal retraction and myelination. Callosal growth therefore is vulnerable for adverse events such as perinatal asphyxia, but there are also genetic and epigenetic factors that determine form and thickness. MRI scans of 110 children, either with specific learning disabilities (LD), i.e. dysphasia/dyslexia, or with several degrees of general LD, showed callosa that were highly variable in size. The callosal size corrected for brain size did not vary significantly according to the severity of the LD, although it tended to be smaller in severe LD, i.e. mental retardation. Callosal size varied however, due to the likely presence of genetic influences or of adverse perinatal events. Children with familial dysphasia/dyslexia, had a thicker CC, possibly reflecting a poorly understood neurodevelopmental mechanism that inhibits the establishment of cerebral dominance. LD children (all subgroups together) with perinatal adverse events had a smaller CC than the familial cases, suggesting CC damage. Despite a multitude of developmental factors influencing the final size, this study suggests that total callosal size, supposedly linked to interhemispheric function, may contribute to the pathophysiological mechanisms that give rise to LD.

Adolescent↗