Steven Pinker in The New Republic
The strange emotional power of swearing–as well as the presence of linguistic taboos in all cultures– suggests that taboo words tap into deep and ancient parts of the brain. In general, words have not just a denotation but a connotation: an emotional coloring distinct from what the word literally refers to, as in principled versus stubborn and slender versus scrawny. The difference between a taboo word and its genteel synonyms, such as shit and feces, cunt and vagina, or fucking and making love, is an extreme example of the distinction. Curses provoke a different response than their synonyms in part because connotations and denotations are stored in different parts of the brain.
The mammalian brain contains, among other things, the limbic system, an ancient network that regulates motivation and emotion, and the neocortex, the crinkled surface of the brain that ballooned in human evolution and which is the seat of perception, knowledge, reason, and planning. The two systems are interconnected and work together, but it seems likely that words’ denotations are concentrated in the neocortex, especially in the left hemisphere, whereas their connotations are spread across connections between the neocortex and the limbic system, especially in the right hemisphere.