"Tickling the rat" has got to be a euphemism for something. But it's also a way of studying the neurobiology of depression.
At least that's what Wöhr et al say in a new paper. They started from the fact that when you tickle rats, some of them seem to enjoy it, and express this by making 50 kHz squeaks of joy. But other rats don't like it, and they make a different sound, much lower at 22 kHz. (These sounds are all too high for most humans to hear, but they can be recorded electronically.)
Whether a given rat is cool with being tickled seems to be a fairly stable individual trait. Some do, some don't. And rats which don't like being tickled tend to be generally anxious and neurotic in lots of other ways. They're the Woody Allens of the rat world, maybe.
Wöhr et al decided to see ...
