Functional magnetic resonance imaging (fMRI) studies have shown that the higher and lower parts of the brain can struggle with each other when a person swears [ref]. A New York Times article cites several other studies that involve how a healthy brain processes swearing. For example, the brains of people who pride themselves on being educated respond to slang and "illiterate" phrases the same way they do to swearwords. In addition, in studies in which people must identify the color a word is written in (instead of the word itself), swearwords distract the participants from color recognition. You can also remember swearwords about four times better than other words [ref].Link (via Digg)
Swearing can also be a symptom of disease or a result of damage to parts of the brain. We'll look at swearing and brain disorders next.
(Creative Commons-licensed image, oh ( ---- )!!! ganked from Debaird's Flickr stream)
Update: Get your cussin' button here