Injecting human growth hormone or similar growth factors into the brain may stimulate some growth, such as increased branching or sprouting of new neuronal terminals, but this is highly dependent on the injection site and the presence of specific receptors. In a mature brain, significant growth and rearrangement are not typical, as most neurons are retained for life, with limited exceptions. Additionally, the confined space within the skull poses challenges; growth in one area could disrupt functionality in another. Research is more focused on using growth factors in diseased or injured brains, where the main challenges include targeting the right growth factors, delivery methods, and duration of exposure.