If you are a materialist holding the logical belief that the human brain, with all of its buzzing neural intricacies, its pulpy, electrified, arabesque chambers and labyrinthine coves, has been carved out over countless eons by the slow-and-steady hand of natural selection, then you will grant that specific brain regions evolved because they generated behaviors that were beneficial to our ancestors. When one part of the brain is compromised—through injury, disease, or some other unfortunate event—the constellation of symptoms that result are often remarkably specific. "The brain is the physical manifestation of the personality and sense of self,"writes University of Michigan neuroscientist Shelley Batts in a 2009 issue of Behavioral Sciences and the Law, "and focal damage to brain areas can result in focal changes in behavior and personality while leaving other aspects of the self unchanged."
Not to get too technical, but if you're unlucky enough to develop a lesion that interferes with the functioning of your dorsolateral prefrontal cortex, a specialized patch of neural tissue that's intricately braided into your anterior cingulate cortex, then your working memory, strategy-formation, and planning skills are going to take a major nosedive. Something as simple as coming up with a list of groceries that you'll need for the next few days becomes a major achievement.
Most of us—materialist and dualist alike—have sympathy aplenty for those patients whose brain disturbances have interfered with their everyday cognitive abilities. We're perfectly willing to accommodate their intellectual disabilities by, say, helping them create a new mnemonic strategy or giving them a pat on the back or a word of encouragement when they're trying to remember someone's name. Yet when chunks of gray matter that have evolved to control and inhibit, say, our sexual appetites and other Bacchanalian drives experience a similar catastrophic blowout, are we so understanding? What if those impairments lead their victims to display … oh, I don't know, let's call them moral disabilities? Cases of libidinal brain systems going haywire have our kind-hearted, humanistic materialism rubbing elbows—or butting heads—with our belief in free will and moral culpability.
Although Klüver-Bucy Syndrome is relatively rare, it's one of the most notorious neurological causes of a complete breakdown in one's ability to control sexual urges. In 1939, neuroanatomists Heinrich Klüver and Paul Bucy removed the greater portions of both temporal lobes and the rhinencephalon from the brains of rhesus monkeys. Among a host of other peculiar effects of this rather cruel vivisection, the monkeys became incredibly randy, displaying a prominent and indiscriminate desire to copulate. The first documented case of full-blown Klüver-Bucy in humans arrived in 1955, when an epilepsy patient underwent a bilateral temporal lobectomy (a surgical excision of the lobes) and subsequently developed a ravenous sexual appetite, among other things. More often, the syndrome appears in lesser degrees, precipitated by a nasty insult to the medial temporal lobe. That might result from a case of herpes encephalitis or Pick's disease, or from trauma and oxygen deprivation. Not all such patients experience hypersexuality, mind you, but some do. Other symptoms aren't terribly appealing, either, however; they include hyperorality (a compulsive desire to put things in one's mouth), apathy, emotional unresponsiveness, and various sensory disorders.
Dramatic case studies illustrating the devastating effects of Klüver-Bucy Syndrome abound in the clinical literature, and they raise intriguing philosophical questions for us to consider. That some patients so stricken are overcome with excessive carnal urges and are not simply using the disorder as a convenient excuse to become freely promiscuous, lewd, and lascivious is perhaps best demonstrated by a 1998 Clinical Neurology and Neurosurgery study by Indian neurologist Sunil Pradhan and his colleagues. In this report, a group of boys between the ages of 2.5 and 6 began to exhibit hypersexualized behaviors after partially recovering from comas induced by herpes encephalitis. One to three months after emerging from the comatose state, "all seven children," note the authors, "demonstrated abnormal sexual behavior in the form of rhythmic hip movements (two patients), rubbing genitals over the bed (two patients) and excessive manipulation of genitals (all seven patients)." Were these children just helpless, hapless puppets of their ancient, pleasure-driven brains? The authors believe so. "As all patients [at the time of study], except one, were 4 years of age, with no possibility of environmental learning of sex, these movements most probably represented phylogenetically primitive reflex activities."
It may be awkward enough telling other parents why your preschooler is humping everything in sight—just try rehashing the foregoing description of Klüver-Bucy Syndrome to your friends at the day care—but we do tend, as adults, to be mostly forgiving of a child's improprieties. When this sort of hypersexuality strikes a post-pubescent individual whose sexuality is driven by orgasm-propelled desires, things become more interesting—at least, in a philosophical sense. Although it would be entirely inaccurate to portray Klüver-Bucy patients as sex-crazed lunatics, they very often display behaviors that would be considered inappropriate by conventional standards. One gentleman in his early 70s, for instance, hugged a female parishioner at his church and repeatedly kissed her. According to the clinical case report, he then asked the shocked woman, "Why don't we do it again?" Over the ensuing years, his sexual fantasies skyrocketed and his hyperorality became unmanageable. The report notes that, according to his wife, "he would put any object in his mouth, including dog food, candles, adhesive bandages, and his wedding ring. His appetite seemed insatiable. … He died at age 77 years of asphyxiation on several adhesive bandages."
In a 2005 letter to the editor of European Psychiatry, two physicians describe the case of a 14-year-old schoolgirl ("Ms. A"), who, prior to developing Klüver-Bucy Syndrome after being in an encephalitis-caused coma, "was an intelligent and social girl with a good academic record." This quiet, well-behaved teenager became somewhat challenging, to say the least, after recovering from her illness. You think you're raising a difficult teen? Consider what these parents were dealing with: