I think you might be missing the point, though. The argument is that we're collecting exponentially more data about the brain, but that data doesn't translate directly to understanding.
You mentioned Phineas Gage. That case led to the idea of regions of the brain controlling different things, which led to lobotomy as a psychiatric treatment, which was used up until the 1960s or so. Then chemical methods improved, and people came to understand that neurotransmitters played a role too, which led to antidepressants and other drugs. Those drugs have improved, but their design hasn't changed that much in the last few decades. Obviously this is over-simplified -- but it doesn't sound like an exponential growth of understanding to me.
At the end, we can't talk about exponential or linear growth. We have no 'mesure' for scientific advance. and we need mesure for mesuring something. Or maybe somes exist but I'm not... okay so I googled it before posting some stupid stuff: It seems that there's no 'real' mesure.. scientific paper to prove it: http://www.springerlink.com/content/m1h2150x02u153x3/
You mentioned Phineas Gage. That case led to the idea of regions of the brain controlling different things, which led to lobotomy as a psychiatric treatment, which was used up until the 1960s or so. Then chemical methods improved, and people came to understand that neurotransmitters played a role too, which led to antidepressants and other drugs. Those drugs have improved, but their design hasn't changed that much in the last few decades. Obviously this is over-simplified -- but it doesn't sound like an exponential growth of understanding to me.