Tickling is caused by a light sensation across our skin. At times the light sensation can cause itching; however, most of the time it causes giggling. Yngve Zotterman from Karolinska Institute has found that tickling sensations involve signals from nerve fibers. These nerve fibers are associated with pain and touch. Also, Zotterman has discovered tickling sensations to be associated not only with nerve fibers but also with the sense of touch because people who have lost pain sensations still laugh when tickled. Research has shown that laughter is more than just a person’s voice and movement and that it requires the coordination of many muscles throughout the body. Laughter also increases blood pressure and heart rate, changes breathing, reduces levels of certain neurochemicals (catecholamines, hormones), and provides a boost to the dying immune system. Can laughter improve health? It may be a good way for people to relax because muscle tension is reduced after laughing.  Even though we may know more about what parts of the brain are responsible for humor, it is still hard to explain why we don’t laugh or giggle when we tickle ourselves. Darwin theorized within “The Expressions of the Emotions in Man and Animals” that there was a link between tickling and laughter because of the anticipation of pleasure. Because we cannot tickle ourselves and have caused laughter, Darwin speculated surprise from another person touching a sensitive spot must have caused laughter.