I began doing research stuff during 1st year although not all of it neurosurgery related. I think it depends on how well you feel you can handle both...don't sacrifice doing well on Step 1 for research sake, but it would be best to do both. Third year rotations can be pretty busy (usually people would say you're going to have less free time during 3rd year than you would during 2nd year). There is no reason you couldn't continue 2nd year, study for Step 1, and do some chart-review type research at the same time. Writing up a case report can be a fairly quick way to get something published although research project will also look better.