Dayanidhi S, Hedberg Å, Valero-Cuevas FJ, Forssberg H. Developmental improvements in dynamic control of fingertip forces last throughout childhood and into adolescence.

Little is known about the development of postural adjustments during early ontogeny. We examined postural adjustments due to sudden perturbations during sitting in 40 healthy term infants (28 males, 12 females) assessed in groups of eight at 1, 2, 3, 4, and 5 months of age. Surface electromyograms of neck, trunk, and leg muscles were recorded while the infants were exposed to a random series of horizontal forward and backward displacements of the surface of support. Video recordings of spontaneous motor behaviour were analyzed. For part of the analyses, previously collected data on 26 infants aged 6 to 10 months were included. In general, postural adjustments at all ages were direction specific and showed large variation. Within the variation developmental changes could be observed, revealing a transient decrease in postural activity at 3 months of age. After this transition, direction-specific postural activity was correlated with spontaneous motor behaviour. This was true, in particular, for dorsal postural activity. The clinical relevance of these findings is discussed.

The aim of the study was to examine whether infants, at an age when they have no or little experience in sitting, can produce direction specific postural adjustments, i.e. synergies of muscle activity on the ventral side of the body during backward sway and on the dorsal side during forward sway. In addition, we addressed the question whether postural adjustments at this young age are restricted to single muscle responses or consist of a variable repertoire of muscle activation patterns including one during which all direction specific muscles participate ('complete' pattern). Postural adjustments due to external perturbations in a sitting position were studied in eight healthy infants aged 1 month. Multiple surface EMGs of neck, trunk and leg muscles and kinematics were recorded while the infants were exposed to horizontal forward (Fw) and backward (Bw) displacements of the surface of support. Direction specific postural adjustments, defined as adjustments during which agonist activation or antagonist inhibition preceded antagonist activation, were present in 85% of Bw and 72% of Fw translations. The direction specific adjustments showed a large variability with the repertoire of adjustments including the activation of one, two or all of the recorded direction specific muscles. The finding of direction specific adjustments at 1 month of age support the opinion that the basic level of organisation of postural adjustments has an innate origin. The finding of a variable repertoire of muscle response patterns, including the 'complete' pattern, refutes the idea that the development of postural adjustments results from gradual addition of appropriate muscles to the synergies.

The electron spin resonance spectrum of +H3NĊHCOO− in single crystals of glycine γ irradiated at room temperature has been re-examined at X band and evaluated by resolution-enhancement technique. The resolution enhancement is obtained by reducing the linewidth by a factor of maximum 0.55 at the expense of the signal-to-noise ratio. The calculations, which require a high-speed digital computer, consist of three steps: (1) transformation of the experimental spectrum to a complex Fourier plane, (2) multiplication of this Fourier spectrum with a suitable linewidth-reduction function, and (3) inverse transformation back to the real plane. From the obtained constants, the hyperfine coupling tensors have been calculated, including contributions from second-order effects (ΔMI = ± 1). One of the principal values of one of the tensors was appreciably affected by these second-order effects. The results fully confirm the structure of the radical.

Little is known about the development of postural adjustments during early ontogeny. We examined postural adjustments due to sudden perturbations during sitting in 40 healthy term infants (28 males, 12 females) assessed in groups of eight at 1, 2, 3, 4, and 5 months of age. Surface electromyograms of neck, trunk, and leg muscles were recorded while the infants were exposed to a random series of horizontal forward and backward displacements of the surface of support. Video recordings of spontaneous motor behaviour were analyzed. For part of the analyses, previously collected data on 26 infants aged 6 to 10 months were included. In general, postural adjustments at all ages were direction specific and showed large variation. Within the variation developmental changes could be observed, revealing a transient decrease in postural activity at 3 months of age. After this transition, direction-specific postural activity was correlated with spontaneous motor behaviour. This was true, in particular, for dorsal postural activity. The clinical relevance of these findings is discussed.

This study investigates the early development of postural adjustments during external perturbations in two different standing positions: standing with support and standing without support. The aim of the study was to assess a group of 13 infants four times during the period in life when independent standing is achieved; at 8, 10, 12 and 14 months. However, longitudinal data could be achieved only in four infants. Muscle activations of the neck, hip and ankle were recorded using surface electromyography. Based on earlier studies and controversies, three main issues were addressed: (1) Is direction specificity present before independent standing is established? (2) How do postural adjustments change with increasing age (8-14 months)? (3) Are postural adjustments task-specific in the young child? The results showed that our small sample of infants aged 8 and 10 months, who were not yet able to stand independently, exhibited direction-specific postural adjustments both during standing with and without support, though not consistently during all trials and at all body levels. Therefore, we argue that direction specificity might constitute a prerequisite for the development of independent standing. We also found that the development of postural adjustments in standing with support resembles that of sitting, i.e. great variation in the postural adjustments at early age, and fine-tuning to the situation with increasing age and experience. This, we find that this is in agreement with the proposal that postural control develops through a selection process of the most suitable postural adjustments for the situation from a repertoire of direction-specific postural adjustments. The development of postural adjustments during standing without support is discussed. Additionally, differences in response rates were noted between the two standing positions, indicating that even before independent standing is established, sophisticated sensorimotor integration enables task-specific postural adjustments.

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