Human beings are some of the most complex organisms on the planet, not just in terms of pure biochemistry, but in the way we have cognitive thought processes, feel emotions, and perceive the world around us. We have a constant internal narration and multiple conscious and unconscious thoughts all the time, and our bodies help us to experience and explore our surroundings. But where is the line between physical being and conscious thoughts that defines who we are? Ignoring the ethical concerns attached to the idea of a brain transplant, I wonder what would happen to a person if they received a new brain – who would they be?
When initially looking at the structure and function of the brain, I believed there would be a few key areas that make all individuals unique in terms of who they are: the parietal lobe (in the cerebrum) the hippocampus, the cerebellum and the limbic system (under the cerebrum). The parietal lobe is important for interpreting words, sensing touch, sound and pain, interpreting sensory stimuli, and spatial awareness – this is a part of the brain that helps determine how, as individuals, perceive the world around us. The hippocampus is where long term memories are ‘stored’ and the limbic system is the area where emotions stem from.
However, there appear to be lots of areas that interpret sensory stimuli, and although the hippocampus is the main area associated with memory, there are other areas that do this as well. Interpretation of language occurs in the temporal lobe too, not just the parietal lobe. It is easy to see that the brain is intricate and complex, and within the gross structure it is difficult to isolate parts that determine who we are – I suppose it depends how you classify people. Some would argue that the cerebral cortex, where logical thinking comes from, while others would argue that the limbic system, as a source of emotions, is where the real inner self arises from.
Hypothetically, if a person was to have a brain transplant I would say that the original “owner” of the transplanted brain is the person that would still be alive following the procedure, just in the body of someone else. If all the nervous connections were remade, then I imagine then that brain would perceive the world from a new body with altered senses, given their new sensory connections. All the information such as memories would be stored in the brain and so the person leaving the operation would have memories from living in a whole different body… spooky! It is also worth noting that the muscle memory and co-ordinated control of gross motor skills and posture (as controlled by the cerebellum) would all be in-tune for the previous body, so the new person could be clumsy following the operation as the brain registers the new relative positions of their limbs.
There are so many things to consider before even looking at the ethical issues with regards to brain transplant. I think it is a very interesting thought experiment to work out which person – the brain or the body – would really come out of the operation.