Rat's Laughter

This video is what first inspired me to look into listening to rats ultrasonic vocalisations.

It has now been proven that rats laugh. We cannot normally hear this though, as it is at a high ultrasonic frequency of around 50 kHz. Younger rats seem to be more susceptible to laughing, and they are generally more playful than older rats. It also seems that some rats are more playful and ticklish than others. The rats who enjoyed tickling would also seek out the human hands which had tickled them in the past. They also laughed less when around the smell of a cat, when too hungry, or around bright lights (rats prefer dim lights). In adults, it also seems that females prefer tickling to males, and that it is difficult for an adult rat who has never been tickled to start enjoying the behaviour. When young rats get to choose between adults, they prefer to spend time with the adult who 'laughs' more.

It seems that rats laughter is distinct from their other ultrasonic vocalisations. They talk to each other, and only sometimes do we hear these vocalisations - for example when play fighting. By using a piece of equipment to listen to their usually unheard noises we can find out more about them.

In the paper called "Tickling-induced 50-kHz ultrasonic vocalization is individually stable " by Mallo et al. they mention that they studied low frequency vocalisations of rats:
and predicts behaviour in tests of anxiety and depression in rats

"We also studied the emission of low-frequency USVs in the

range of 20-kHz, that have long been associated with negative

events and stimuli and 50-kHz USVs and hence the emotional messages they carry

are mutually exclusive or not, the associations between the two

types of USVs were assessed, and no correlations were found."

This shows that rats also have lower frequency vocalisations which are different to their higher frequency ones, and carry different meanings.

http://blogs.scientificamerican.com/bering-in-mind/2010/08/03/laughing-rats-and-ticklish-gorillas-joy-and-mirth-in-humans-and-other-animals/

http://www.onesci.com/w/wix/images/0/0a/Tickling_Rats.pdf