1. Genes - are a major key factor in brain development due to their contribution to normal individual variation in brain development, and relatively rare genetic alterations.
2. Environmental factors - Because having a safe and nurturing environment facilitates proper growth.

It's been thought that the neurons were already created before birth, but research indicates that the brain keeps growing until mid to late childhood, decreases through the early 20s, stabilizes for quite a while, and then begins to decrease further from age 40 onwards.

• Neurogenesis is the process by which new neurons are created. The bulk of this process happens during the prenatal period of brain development.
• Synaptogenesis is the process of forming connections or synapses.
• Synaptic pruning is the process where synapses that aren't used grow weaker and disappear.
• Myelination is a key process in neuronal development that begins before birth

• Also known as neural plasticity
• This is the capacity of the brain to change in response to experience and the environment.
• It changes the brain from updating the neuronal networks to the formation of new memories to larger structural adaptations.
• The brain has a great amount of plasticity and it remains an essential quality of the brain throughout adulthood.