What exactly is a tickle? In scientific terms, nerve signals are sent from the skin to the primary somatosensory cortex, which is the part of the brain that controls the sense of touch. These signals are analyzed by the anterior cingulate cortex, which is the part of the brain that responds to pleasant feelings. The messages also generate activity in the hypothalamus, which is responsible for instinctive involuntary reactions to situations that might involve pain.

The automatic response from the hypothalamus prepares us for an incoming attack, triggering an involuntary self-defense mechanism designed to protect the most vulnerable parts of our body by curling up. So one part of the brain is saying, “You’re under attack!” while another part of the brain is saying, “This feels good!” This is why tickling can be both wonderfully fun, and also horribly torturous.

When you try to tickle yourself, the messages go to the cerebellum, the part of the brain that governs our movements. There is no kick of adrenalin from the hypothalamus. However, some people with schizophrenia can tickle themselves.

When test subjects were placed in an MRI, being tickled activated the hypothalamus. Laughing at jokes and comedy did not.

There are two different types of tickle, with scientific names for both. Knismesis comes from the Greek word for itching. This is the type of tickle an ant makes when it’s walking up your leg, or a feather brushes your arm.

Gargalesis, from the Greek word for tickle, is the giggle-type of tickle.

The word tickle comes from the Latin “titillare” which also gives us “titillate.”

    Tickling is usually a two-way street where the tickler and the ticklee both laugh. Researchers wanted to know: Will babies laugh even if the tickler is disguised with a full face mask? Answer: Yes.

•    Will tickled babies laugh even if they are born blind and deaf? Answer: Yes.

Researchers performed a series of experiments involving robotic arms. Would people still laugh if they were being tickled by a human arm cleverly disguised as a robotic arm? Answer: Yes. Would they laugh if tickled by a real robotic arm? Answer: Yes. Would they laugh if they controlled the robotic arm’s tickling motion using a joystick? Answer: No. Would they laugh if the joystick motion of the robotic arm was delayed by five seconds? Answer: Yes.

•    Are other animals ticklish? Yes, all primates are ticklish, and they are ticklish in the same spots that humans are ticklish. Most primates even employ a grunting form of laughter.

•    Meercats, penguins, and owls are ticklish.

•    Rats, when tickled, laugh in a supersonic giggle that is beyond the range of human hearing. Not all rats enjoy being tickled, with many adult female rats disliking it.

•    When tickled, we instinctively curl up, turn away, squirm, twist, scream, and kick trying to get away, while also laughing and smiling. Scientists believe this is a safe and friendly way of teaching each other how to protect ourselves when attacked. When puppies play-fight, they are learning how to handle an opponent. If attacked by a predator, they know how to protect themselves. Similarly, when parents play “Tickle Monster” with a toddler, the child practices rudimentary self-defense mechanisms.

•    If a complete stranger starts tickling a child, catching them by surprise, the reaction to the tickle attack is not laughter but fear.