It definitely is not the case for all institutions! It depends on your programs of interest but I had an entirely different interview experience at both of my interviews (one ivy league-waiting on response, another one-got accepted). Professors at both programs were friendly and passionate about their research and wanted to see if you were the same. Of course the general questions, "Why Neuroscience, why graduate school, why now?" all came up in conversation but it came off as a more casual probing because they didn't want you to be nervous. You still needed to give good answers, though. Make sure you channel your nerves into excitement for your research. Have a clear direction of what you want to study and where you want to be. You are not expected to know everything about your field, and be honest but inquisitive when you don't. My personal tip that I think got me my acceptance: read a paper of the professor's in advance and prepare very thoughtful questions that show you can think about the scientific process, see the bigger picture of research, while simultaneously allowing them to talk about themselves. You'll ask other questions as the natural conversation flows along, but have some prepared, with a pen and paper, for each interviewer. Avoid empty silence at all costs. They want someone that they can see themselves interacting with for ~5-6 years. Both interviews I ended up over-preparing, but that's not a bad thing.