In the past few years, I've become very interested in neuroscience and I've read and studied a great deal about it. Unfortunately, the local universities don't have a neuroscience specialty, so a PhD is out of the question unless I relocate.
Computer science and neuroscience really go hand-in-hand these days. There's a great deal of research being done from the modeling of just ion channels to the modeling of entire cells, to the modeling of large-scale brain structures.
My personal belief is that software, based on neuroscience principles, will become an important area of software development for writing intelligent systems. Systems that can effectively recognize voices, faces, or interpret language, etc, are natural targets. Imagine a stock picking system that reads news stories and factors in emotional content into its picks (after all, let's face it, since the internet made stock-trading more accessible, emotion plays much heavier into the market). Systems could be designed that could monitor financial transactions to find and identify novel types of fraud. In astronomy, because of the number and quality of images coming in, one could create systems that could intelligently view the volumes of images and identify and catalog new objects.
Really, it's an area that's wide open to possibilities. But to understand how to properly piece together the types of artificial neural circuits to accomplish this kind of functionality, one would need a fairly good understanding of how the various circuits in a human brain connect and interact and how they are used to process information (we already understand a tremendous amount about this and we're learning more all the time). Really, neuroscience seems to me to be the new computer science. It's where some of the most amazing advances are being made in science today, in my opinion.
But it is just my opinion and there are lots of other possibilities. I'm definitely enthusiastic about this..