Maturation of inhibitory and excitatory motor cortex pathways in children

Division of Neuropediatrics and Muscular Disorders, Department of Pediatrics and Adolescent Medicine, University of Freiburg, Mathildenstrasse 1, 79106 Freiburg, Germany.
Brain & development (Impact Factor: 1.88). 04/2009; 31(7):562-7. DOI: 10.1016/j.braindev.2009.02.007
Source: PubMed


To study intracortical inhibition and facilitation with paired-pulse transcranial magnetic stimulation in children, adolescents and adults.
Paired-pulse transcranial magnetic stimulation (interstimulus intervals (ISI): 1, 3, 5, 10 and 20 ms) was applied over the primary motor cortex (M1) in 30 healthy subjects (range 6-30 years, median age 15 years and 8 months, SD 7,9) divided in three groups: adults (>or=18 years), adolescents (> 10 and < 18 years) and children (<or=10 years).
We observed significantly less intracortical inhibition (SICI) in children's M1 compared to that of adults. Adolescents showed significantly less SICI at the 5 ms interval than did adults. No significant differences were apparent in intracortical facilitation (ICF).
We postulate that, as in adults, the maturing M1 possesses horizontal glutamatergic cross-links that represent the neuronal substrate of excitatory intracortical pathways. GABAergic interneurons, the neuronal substrate of inhibitory intracortical pathways, mature between childhood and adulthood. Reduced GABAergic inhibition may facilitate neuronal plasticity and motor learning in children.

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    • "However, only a few SICI studies in pediatric populations contributed to the understanding of neuromotor maturation and motor skill deficits (Garvey and Mall, 2008; Schneider et al., 2008). To date, it is known that less SICI can be detected in M1 of healthy fullterm children as compared to adults (Mall et al., 2004; Walther et al., 2009), but no TMS data is available in the preterm population for tackling the underlying neural mechanisms of motor coordination disorders. "
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    • "Sensorimotor cortex synaptic density decreases markedly in adolescence and plateaus in young adulthood before a further progressive reduction in synaptic density begins in the fourth decade (Huttenlocher, 1979, 1990; Huttenlocher and Dabholkar, 1997; Dickstein et al., 2007). Intracortical inhibition is not mature until adulthood and is reduced in the elderly (Peinemann et al., 2001; Mall et al., 2004; Walther et al., 2009). The morphological properties of alpha-motoneurons and their excitatory and inhibitory control mature during development and are altered in the elderly (O'Sullivan et al., 1991; Erim et al., 1999; Mc Donough et al., 2001; Mentis et al., 2002; Furlan et al., 2007; Carlin et al., 2008; Sibilla and Ballerini, 2009). "
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