Final answer:
Fetal brain tissue is more successful in brain grafts due to its plasticity, adaptability, and abundance of stem cells.
Step-by-step explanation:
The success of brain grafts is much better when brain tissue from the fetal stage is used because during fetal development, the brain is in a highly plastic and malleable state. It has the ability to grow and adapt to its environment more effectively compared to the adult brain. Additionally, fetal brain tissue contains a higher number of stem cells, which are capable of differentiating into various types of brain cells. This increases the chances of successful integration and functionality of the graft in the recipient brain.