Update in Development: Section A—Infant Development

Abstract

The early childhood period (birth to age 5) is considered to be the most important developmental phase throughout an individual’s life. The human brain is the ‘master organ’ of development, which undergoes its most sensitive periods in its early years of life (Grantham-McGregor et al. 2007; Shonkoff et al. 2009; National Research Council and Institute of Medicine 2000). The development of neurons is mostly completed at birth, but the interconnections between neurons i.e. the synapses—are still developing at an incredible rate. 700 synaptic connections form per second in a child’s brain in the first few months of life, a rate that is unrivalled throughout his or her lifespan (Zero to Three 2002; Center on the Developing Child Harvard University 2012). The formation of synapses peaks between the third trimester of pregnancy and the second birthday. Synaptogenesis then continues throughout childhood into adolescence, but at a slower rate. Basic sensory circuits like vision, hearing and touch form first. These serve as foundation blocks for the development of more complex brain circuits, responsible for reflective thinking, behavior and cognitive functions. Synapses that are stimulated by frequent use during early years get hardwired, whereas those that are rarely used are eliminated by a process called ‘pruning’. Repeated pruning results in a sophisticated brain architecture of intricate neural connections.