Twenty years ago no one cared about emotions and the brain, but it seems in the last couple of years there's been a flurry of activity. One reason for this may be that the topic was ignored for so long, and the vacuum is being filled. Another, though, is that there have been some successes in approaching the problem, and these have changed peoples' minds about the feasibility of studying emotions in the brain. The most successful efforts have come from the study of fear.
Fear is a relatively tractable emotion, unlike love or hope which are difficult to pin down.
It's always easier to study brain functions that involve clearly defined stimuli and responses than those that don't. For fear, you can easily create experimental situations where the onset of a simple stimulus that warns of impending danger elicits a set of stereotyped responses in an animal, like a rat, that are very similar to the kinds of responses that occur in a human facing danger. By following the flow of the stimulus through the brain from the stimulus processing pathways to the response control networks, it's possible to identify the basic neural circuits involved. We've done this for fear. I got interested in emotions while I was studying something completely different.