by default you can't, there's no option for it to happen. At the moment the options are to click on the button that says 'go to first unread' which will obviously take you to the first one you've not read.
There's no 3rd party addon that we can use so this is likely to be something that we might be able to do in the future but it's not an easy fix at the moment.
Sorry that's not more helpful, there might be another work around that we've not discovered yet, if we do we'll let you know.