Existing Challenges
One of the most significant barriers to the procedure is the inability of nerve tissue to heal properly; scarred nerve tissue does not transmit signals well (this is why a spinal cord injury is so devastating). However, recent research at the Wistar Institute of the University of Pennsylvania involving tissue-regenerating mice (known as MRL mice) may provide pointers for further research as to how to regenerate nerves without scarring.
There is also a potential problem of the new interface at the spinal cord, in that even if all the nerves are connected successfully, they may still be connected wrongly, thus not transmitting the same information as the same nerve connection in the previous body. For example, a nerve that used to control the right index finger's muscle group might be connected to a different finger's muscle group, or another body part entirely. If this were to happen to a large number of connections, the person undergoing the transplant might end up with a body which transmitted sensory input to the wrong destination, making it incomprehensible and potentially requiring many years of rehabilitation.
Alternatively a brain–computer interface can be used connecting the subject to his own body. A study using a monkey as a subject shows that it is possible to directly use commands from the brain, bypass the spinal cord and enable hand function. An advantage is that this interface can be adjusted after the surgical interventions are done where nerves can not be reconnected without surgery.
Also, for the procedure to be practical, the age of the donated body must be sufficient: an adult brain cannot fit into a skull that has not reached its full growth, which occurs at age 9–12 years.
There is an advantage, however, with respect to the immune response. The brain is an immunologically privileged organ, so rejection would not be a problem. (When other organs are transplanted, aggressive rejection can occur; this is a major difficulty with kidney and liver transplants.)
Read more about this topic: Brain Transplant
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