Brain development is the process through which neurons form and mature, and it is divided into six stages: proliferation, migration, differentiation, synaptogenesis (the formation of synapses, the connections between neurons), myelination, and apoptosis. This process begins during pregnancy and continues until the end of adolescence.

Exposure to environmental factors during this period can lead to altered brain development and affect cognition, such as: decreasing IQ, or increasing the risk of developing different disorders such as autism or attention deficit hyperactivity disorder (ADHD).