Ticklish Giggling Rats  

Scientists do not know why tickling results in happiness or why certain body parts are more susceptible to the sensation than others, or why the best tickles occur at the hands of others. So rats were selected because young rats not only feel the sensation, but are also most ticklish on the belly and the bottom of the their feet. While rats do enjoy tickling, their laughs are long 50 kHz ultrasonic calls that are soundless to humans. In the somatosensory cortex, the part of the brain associated with touch, when a rat is tickled, neurons located at the stem of the cortex come alive instantaneously. The somatosensory cortex is the brain’s tickling epicenter, at least when it comes to rats.  The brain’s identical response to playing and tickling indicates that tickling is a trick by the brain to inspire social contact and affection. The neurons began to fire long before the tickling began, this anticipation can only take place when there is social interaction with another individual. Even the most ticklish rats do not respond when they were in a bad mood.  

https://www.linkedin.com/pulse/ticklish-giggling-rats-randy-bilesky?published=t

http://www.delta-optimist.com/opinion/blogs/blog-ticklish-giggling-rats-1.9710591

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