Prenatal growth and early postnatal influences on adult motor cortical excitability

Suboptimal prenatal growth may adversely influence motor neurophysiologic development and predispose the individual to greater risk of neurodegenerative disorders in later life. We investigated the influences of prenatal growth and the postnatal environment on motor cortical function in young adults.

Transcranial magnetic stimulation was used to construct corticospinal stimulus-response curves for 35 young adults (mean age: 28 +/- 0.5 years; 19 males) born >or=37 weeks' gestation. Birth weight centile was calculated relative to maternal size, parity, ethnicity, gender, and gestation. Handgrip strength and dexterity were measured separately. Regression analyses assessed the influence of prenatal (birth weight centile and gestation) and postnatal (socioeconomic indices and maternal education) factors on corticospinal parameters, strength, and dexterity scores.

Lower birth weight was associated with increased interhemispheric asymmetry in motor threshold and increased cortical stimulus-response curve slope. A shorter gestation predicted a larger area under this curve in the right hand. High motor threshold was predicted by greater environmental adversity in early postnatal life, but not by prenatal factors. Higher birth weight centile and lower motor threshold were associated with greater educational achievement.

Poor in utero growth and mild prematurity are associated with altered corticospinal excitability in adulthood. An early postnatal environment with less early postnatal socioeconomic disadvantage and having a mother with a completed high school education partly ameliorates this. While altered cortical development has some functional consequences already evident in early adulthood, it may have a later, additional adverse impact on aging-related changes in motor function.