Scientists have lately sought to map the neural topography of forbidden speech by studying Tourette's patients who suffer from coprolalia, the pathological and uncontrollable urge to curse. Tourette's syndrome is a neurological disorder of unknown origin characterized predominantly by chronic motor and vocal tics, a constant grimacing or pushing of one's glasses up the bridge of one's nose or emitting a stream of small yips or grunts.
Just a small percentage of Tourette's patients have coprolalia - estimates range from 8 to 30 percent - and patient advocates are dismayed by popular portrayals of Tourette's as a humorous and invariably scatological condition. But for those who do have coprolalia, said Dr. Carlos Singer, director of the division of movement disorders at the University of Miami School of Medicine, the symptom is often the most devastating and humiliating aspect of their condition.
Not only can it be shocking to people to hear a loud volley of expletives erupt for no apparent reason, sometimes from the mouth of a child or young teenager, but the curses can also be provocative and personal, florid slurs against the race, sexual identity or body size of a passer-by, for example, or deliberate and repeated lewd references to an old lover's name while in the arms of a current partner or spouse.
Reporting in The Archives of General Psychiatry, Dr. David A. Silbersweig, a director of neuropsychiatry and neuroimaging at the Weill Medical College of Cornell University, and his colleagues described their use of PET scans to measure cerebral blood flow and identify which regions of the brain are galvanized in Tourette's patients during episodes of tics and coprolalia.
They found strong activation of the basal ganglia, a quartet of neuron clusters deep in the forebrain at roughly the level of the mid- forehead, that are known to help coordinate body movement along with activation of crucial regions of the left rear forebrain that participate in comprehending and generating speech, most notably Broca's area.
The researchers also saw arousal of neural circuits that interact with the limbic system, the wishbone-shape throne of human emotions, and, significantly, of the "executive" realms of the brain, where decisions to act or desist from acting may be carried out: the neural source, scientists said, of whatever conscience, civility or free will humans can claim.
That the brain's executive overseer is ablaze in an outburst of coprolalia, Dr. Silbersweig said, demonstrates how complex an act the urge to speak the unspeakable may be, and not only in the case of Tourette's. The person is gripped by a desire to curse, to voice something wildly inappropriate. Higher-order linguistic circuits are tapped, to contrive the content of the curse. The brain's impulse control center struggles to short-circuit the collusion between limbic system urge and neocortical craft, and it may succeed for a time.
Yet the urge mounts, until at last the speech pathways fire, the verboten is spoken, and archaic and refined brains alike must shoulder the blame.
