I LOVED my neuroscience class in college and it was just about the only thing that interested me. The brain is truly fascinating and so complex! How much of the field though is really understood? Is there still a large percentage of neuroscience where there are unchartered waters?
It is impossible to estimate the percent known relative to the unknown but although we know a great deal, I suspect it is a bit like space - as much as we know about the solar system, universe, etc., we probably only know a fraction of what might one day be known.
The paradox when it comes to neuroscience, of course, is that the limits of our knowledge of the brain are directly attributed to the organ studying the brain - the brain.
Major advances have been made in molecular biology and in cognitive neuroscience (neuroimaging) but even here the fields are advancing rapidly. I think much of what we known now is on solid footing and won' be upended later, but rather, we will likely add to what we now know..
The US Gov't decision to fund The Brains initiative will go a long way towards increasing our understanding