Changes in the Spinal Segmental Motor Output for Stepping during Development from Infant to Adult

Abstract

Human stepping movements emerge in utero and show several milestones during development to independent walking. Recently, imaging has become an essential tool for investigating the development and function of pattern generation networks in the spinal cord. Here we examine the development of the spinal segmental output by mapping the distribution of motoneuron activity in the lumbosacral spinal cord during stepping in newborns, toddlers, preschoolers, and adults. Newborn stepping is characterized by an alternating bilateral motor output with only two major components that are active at all lumbosacral levels of the spinal cord. This feature was similar across different cycle durations of neonate stepping. The alternating spinal motor output is consistent with a simpler organization of neuronal networks in neonates. Furthermore, a remarkable feature of newborn stepping is a higher overall activation of lumbar versus sacral segments, consistent with a rostrocaudal excitability gradient. In toddlers, the stance-related motor pool activity migrates to the sacral cord segments, while the lumbar motoneurons are separately activated at touchdown. In the adult, the lumbar and sacral patterns become more dissociated with shorter activation times. We conclude that the development of human locomotion from the neonate to the adult starts from a rostrocaudal excitability gradient and involves a gradual functional reorganization of the pattern generation circuitry.

Spinal motor outputs during step-to-step transitions of diverse human gaits

“…In this study we extended the number of recorded muscles relative to our previous studies (Ivanenko et al, 2006, 2013b). In particular, we included intrinsic foot muscles, which demonstrated their own unique activation patterns with bursts principally around the stance to swing transition of gait (Figure 3).…”

Immature Spinal Locomotor Output in Children with Cerebral Palsy

“…Using these approaches, it has been shown that the development of locomotion in typically developing (TD) children involves a functional reorganization of the spinal locomotor output. In particular, the number of basic muscle activation patterns increases from the neonate to the toddler (Dominici et al, 2011; Lacquaniti et al, 2012a), and the temporal dynamics of MN activation in lumbar and sacral spinal segments undergoes structured functional changes during early locomotor development (Ivanenko et al, 2013a). How these developmental processes are altered in children with CP remains largely unknown.…”

“…Recent work from our group has placed a special focus on the spatiotemporal characteristics of the spinal locomotor output (Dominici et al, 2007, 2011; Ivanenko et al, 2013a; Martino et al, 2015). Some previous studies concluded that the locomotor patterns of older children with cerebral palsy show similarity of the early stages of gait development in healthy children (Leonard et al, 1991; Berger, 1998; Meyns et al, 2012), and these have reported mainly the characteristics and the degree of coactivation of only a few muscles.…”

Baby walkers and the phenomenon of toe-walking

“…По современным представлениям, прева-лирующей является гипотеза о формировании двигательных навыков в виде первоначального «примитивного» паттерна мышечной активно-сти, который сохраняется, но совершенствуется и дополняется новыми элементами по мере раз-вития [19].…”

“…В исследованиях П.И Иваненко установлено [19,21], что особенностью вертикальных дви-жений таза (как точки центра масс) в течение периода формирования ходьбы является отсут-ствие характерного первого пика на диаграм-мах, указывающее на отсутствие выраженного «маятнико образного» характера движения цен-тра масс в фазу опоры. Следовательно, во второй фазе -выпрямления ноги, когда наступает спад опорной реакции (в конце фазы обозначается ее минимум), подъем общего центра масс менее выражен, чем у взрослого человека.…”