Definitely try to think about the processing of biosignals, their classification, and predictions of their future development. It is a new, yet extremely perspective developing the field of research where you can employ many ML and data mining techniques.
You will have it very difficult there because you must simultaneously study and/or cooperate with people understanding the given physiology in detail. Without a deep knowledge of given biological processes, you might become lost.
On the other hand, once you penetrate into the field, it can become a gold mine for new discoveries and methods helping to improve and save the lives of many diseased people.
AI is a general term for lots of projects. Narrow your aim such as classification, detection, optimization, recognition, planning, prediction and etc. You have many options!
Areas lacking normal intelligence, like management and finance, would benefit the most from AI. But I fully agree with Jiří that analyzing biosignals will be rewarding for you personally and maybe also for your fellow (human) beings.