Amygdala

Essentially when the brain sees something that's novel, it has to burn more energy to represent it because it wasn't expecting that. This feeling that things are going in slow motion is a trick of memory. In other words, when you're in an emergency situation a part of the brain called the amygdala comes online, this is your emergency control centre, it lays down memories on what amounts to a secondary memory track, these are very dense memories. And you're noticing everything around you and writing it all down. So when the brain reads that back out, there's such a density of memory there that the brain's only conclusion is that must have taken a long time. And I think this offers an explanation for why people think that time seems to speed up as they grow older. And it's because when you're a child, everything's new to you. You're figuring out the rules of the world, you're writing down a lot of memory, and so when you look back at the end of a year, you have a lot of memory of what you've learnt. But when you're much older and you look back at the end of the year, you're probably doing approximately the same stuff you've been doing for the X number of previous years. And so it seems like the year just went by in a flash.