Neural development in children: A neurophysiological studyDéveloppement nerveux chez l'enfant: étude neurophysiologique

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Abstract

In adult human subjects torque motor imposed angular displacements of the upper limb joints result in two major reflex EMG components as identified by their latency. The shorter latency (SL) component is probably the spinal stretch reflex and the longer latency (LL) reflex component may involve supraspinal structures. Tendon jerk, arising via the spinal reflex pathway, is present in children at birth. In this study the presence and the development of the LL component in wrist flexors was investigated in children between the ages of 2 and 13 years. Kinaesthetic reaction times were tested simultaneously. In young children, the duration of the LL component was much longer than that in adults. The duration decreased slowly from 2 to 6 years, following which a relatively abrupt decrease between the ages of 6 and 8 years took place. After 8 years of age responses looked more adult-like. Kinaesthetic reaction times attained adult-like values after 10 years of age. Various possibilities underlying these observations are discussed.

Résumé

Chez des sujets adultes auxquels des déplacements angulaires des articulations des membres supérieurs ont été imposés par un couple moteur, on observe deux composantes principales des réflexes EMG identifiées par leur latence. La composante de courte latence correspond probablement au réflexe d'étirement spinal et la composante plus tardive du réflexe tardif pourrait mettre en jeu des structures supraspinales. Le réflexes tendineux, qui se produit via la voie du réflexe spinal, existe chez l'enfant dès la naissance. Dans cette étude, la présence et le développement de la composante tardive au niveau des muscles fléchisseurs du poignet ont été examinés chez des enfants de 2 à 13 ans. Les temps de réactions kinesthétiques ont été testés simultanément. Chez les jeunes enfants, la durée de la composante tardive est beaucoup plus longue que chez les adultes. Cette durée diminue lentement de 2 à 6 ans, après quoi, une diminution relativement abrupte survient entre 6 et 8 ans.

Aprés l'âge de 8 ans, les réponses ressemblent à celles enregistrées chez l'adulte. Les temps de réactions kinesthétiques rejoignent ceux de l'âge adulte après l'âge de 10 ans. Diverses possibilités sous-jacentes à ces observations sont discutées.

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      Moreover, evidence is rising that supraspinal systems are playing a crucial role in the handling of postural perturbations (Bolton, 2015; Taube, Gruber, & Gollhofer, 2008) and that there are differences in cortical activity between anticipated and non-anticipated perturbations (Adkin, Quant, Maki, & McIlroy, 2006; Wälchli et al., 2017). Since it is known that the supraspinal system progresses during childhood (Giedd et al., 1999; Maatta et al., 2017) and showing adult-like behavior not until the age of 10 years (Bawa, 1981), the more mature supraspinal control may also positively influence training adaptations in anticipated perturbations in the older group. The findings of the present study are solely based on behavioral data (i.e. platform sway path) as it was not possible to investigate the underlying mechanisms with neurophysiological methods due to higher ethical regulations for children.

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    This work was supported by the B.C. Health Care Research Foundation.

    1

    I am grateful to Dr. R.G. Lee for the use of his computer and to Dr. R.B. Stein for the torque motor. Technical assistance by Mr. David White is appreciated.

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