Neurophilosophy has an excellent article on a man whose brain’s sensation areas have reorganised to integrate a hand transplanted from a corpse, 35 years after the man’s original hand was destroyed in an accident.
The somatosensory cortex is literally a ‘map’ of the body. Each part on this strip of brain corresponds to an area of the body and is involved in perceiving bodily sensation.
We know that the somatosensory map is quite malleable, and can change when limbs are amputated and so no longer feed information into the system.
What happens when new limbs are attached is still largely a mystery as this type of transplant is a relatively new procedure. Nevertheless, this is now beginning to be studied and, as the Neurophilosophy article recounts, it’s starting to show us how the brain responds to a changing body:
One consequence of this functional reorganization is phantom limb syndrome, which Savage experienced for a short time following removal of his hand. This is thought to occur because although the deprived somatosensory cortical region takes on another function, it somehow retains a representation of the amputated limb. As a result, the amputee will occasionally experience sensations, sometimes painful ones, which are perceived to be in the missing body part.
In Savage’s case, it was thought that these changes may be irreversible, because his brain had been deprived of inputs from the right hand for some 35 years. But a team of neuroscientists led by Scott Frey of the University of Oregon now show that this is not the case. In a functional neuroimaging study published today in Current Biology, they report that Savage’s somatosensory cortex has been restored to something like its pre-amputation state, with the transplanted hand “recapturing” the cortical area which represented his own right hand.
The research team have put the full text of the scientific report online as a pdf file if you want to get to the nitty-gritty, otherwise the Neurophilosophy article is an elegant summary of a fascinating study.