There has been an enormous fuss lately about the transplant of face parts from a dead donor to a woman. See some of many google links here. The idea of having another person’s face has probably lead many to think about (their own) personal identity. Would you recognise the new face in the mirror as your own? You probably will through association over time. But will it actually “feel” as yourself? This is a totally new issue to which a door now has been opened. Well, at least if this not a one-time show.
As the limits – technical and ethical – of transplants are now being pushed further, what is up next? What if my hippocampus started to shrink, and my memory or learning ability was fading? Would I accept the offer of receiving a fresh hippocampus from a donor? In years to come, we may well be offered this opportunity. In principle, there would be little difference between receiving a donated heart, liver, finger or brain part. But would the inclusion of the hippocampus lead to that other person’s private memories? I guess the chances for this scenario are non-existent. The brain (and the hippocampus) does not work that way.
Chance is that the first brain transplants would first be performed in “not-ethically-dangeours” areas, such as the brain stem (e.g. in Parkinsonism), or the primary visual cortex. But what if I was offered a new amygdala, or spare parts of my orbitofrontal cortex? These areas are tightly coupled to emotional reactions and “personality” (yes, a mongrel concept).
How likely is it that this can be done on purely technical grounds? Well, to tell you the truth; it’s here already! In 1989 Lehman et al. transplanted the suprachiasmatic nucleus (see image below) from one hamster to another. This nucleus is strategically positioned below (i.e. “supra) the optic chiasma, where the two visual projections from the eye cross. It is known to play a significant role in regulating the sleep-wake cycle, and that ablation of this nucleus permanently disrupts the so-called circadian rythm.
Lehman et al. were able to remove the suprachiasmatic nucleus from one hamster. As expected, this led to a disruption of the dicradian rythm of the animal. Then, a suprachiasmatic nucleus was transplanted from another hamster. What happened was that the circadian rythm – the sleep-wake cycle – of the first hamster was restored! In other words, the sleep cycle of the first hamster could be “repaired” by another hamster’s brain part.
So, brain transplants are certainly feasible as future operations in humans! The questions are therefore: would you accept a brain transplant? Should we do this? Could we draw legal lines between “acceptable” and “unacceptable” spare brain parts? Is the hippocampus OK for transplant but the amygdala not?