Furthermore, their auditory cortex now resembled the typical ferret visual cortex, complete with spatial maps and neurons tuned to detect slants of light.Michael Merzenich, one of the founders of the plasticity field, called this experiment “The most compelling demonstration you could have that experience shapes the brain.” An important discovery closely related to plasticity has been the discovery of neurogenesis.In one particularly audacious experiment, the neuroscientist Mriganka Sur literally re-wired the mind of a ferret, so that the information from its retina was plugged into its auditory cortex.To Sur’s astonishment, the ferrets could still see.This is why blind people can use their visual cortex to read Braille, and why the deaf can process sign language in their auditory cortex.Lose a finger and, thanks to neural plasticity, your other fingers will take over its brain space.The instinct of the reasonable observer is that organic changes of this sort somehow absolve the sufferer of the responsibility that would accrue to a child abuser whose paedophilia was congenital. The chances are that the latter tendency is just as traceable to brain mechanics as the former; it is merely that no one has yet looked.
On the day before he was due to be sentenced to prison for his crimes, he had his brain scanned. When it had been removed, his paedophilic tendencies went away. When the regrowth was removed, they vanished again. His case dramatically illustrates the challenge that modern neuroscience is beginning to pose to the idea of free will.
In fact, the best metaphor for the mind might be our immune system.
Just as our antibodies are constantly altered in response to the pathogens we actually encounter (we do not have the B-cells of our parents, or of our identical twin), the brain is constantly adapting to the particular conditions of our own life.
I’ve spilled a lot of ink elsewhere on this phenomenon, but it’s important to remember that your brain is constantly generating new neurons.
There are two main reasons why I’m not ready to give up on free will. One of the great themes of modern neuroscience is the malleability of the mind.
While a genetic program specifies the gross anatomy of our brain, the all important details are determined by experience.