Performing a human brain transplant is an incredibly challenging task with numerous scientific, technical, and ethical difficulties. Here are some of the major obstacles associated with human brain transplantation:

1. Reconnecting neural pathways: The human brain consists of billions of interconnected neurons, forming complex neural networks. Successfully reconnecting the transplanted brain with the recipient's body would require an intricate and precise reestablishment of these neural pathways.

2. Spinal cord integration: The spinal cord is responsible for transmitting signals between the brain and the body, allowing for motor and sensory functions. Integrating the transplanted brain with the recipient's spinal cord to restore functionality is an enormous technical challenge.

3. Immune system rejection: The human immune system is designed to protect the body by identifying and attacking foreign substances. Suppression of the immune system to prevent rejection introduces a whole new set of risks and complications, including increased vulnerability to infections and other diseases.

4. Ethical considerations: Human brain transplantation raises profound ethical questions. It involves transferring a person's consciousness, identity, and personal experiences to a new body. The implications for personal identity and the psychological well-being of both the donor and recipient are complex and uncertain.

5. Limited knowledge and experimental evidence: Our understanding of the brain is still limited, and many aspects of brain function and consciousness remain elusive.

Given these significant obstacles and ethical concerns, brain transplantation remains purely speculative. The focus of neuroscientific research and medical advancements is primarily directed towards understanding the brain, developing therapies for neurological conditions, and improving brain-computer interfaces.