The development of brain and behaviour are closely linked. The alterations in brain structure results in alteration of behaviour and vice versa.
The function of brain is mostly determined by the inherited genes. However, the gene expression is in turn partly influenced by the environmental factors or epigenetic factors. The other factors that influence the functioning of brain are hormones, trauma and sensory experiences.
Thus, the blanks can be filled with, genes; sensory experiences; hormones.