怎样改变个性？

How to change a personality?

Deep brain stimulation, or DBS, is a treatment given to Parkinson's patients who don't respond to medication. A neurosurgeon implants a set ofelectrodes deep into the victim's brain, where they give off little jolts of electricity to disrupt the involuntary tremors and other symptoms of the disease. But according to Martha Farah, a neuroscientist at the University of Pennsylvania, at least one patient routinely chooses which electrical contact to activate depending on how she wants to feel: calm for every day, more "revved up" for a party.

Devices like DBS and psychoactive drugs like Ritalin and Prozac are already manipulating brain function in millions of people. And future pharmaceuticals, Farah says, targeting very specific parts of the brain, will be even more effective and will have fewer side effects. These new brain-control tools open a Pandora's box of ethical and philosophical dilemmas, including what kind of society--and what kinds of selves--we want.

Indeed, where there once seemed to be a clear boundary between mental health and mental dysfunction, it's now clear that these states lie along a spectrum. "Thirty years ago," says Farah, "only seriously depressed people took antidepressants. But I'm sitting in a coffee shop now where probably half the people have taken them." Some ethicists argue that unless you're ill, you're not really yourself when you're on these drugs. On the other hand, says Farah, we change our brain chemistry no more with Prozac than with coffee or tea.

With that in mind, Farah is studying modafinil, a drug developed for narcolepsy that is prescribed off-label to patients with depression, ADHD or even jet lag. In the military, it's used to sharpen soldiers' alertness and cognition. Her research is attempting to determine how this chemical affects normal people. "Is there a trade-off," she wonders, "between focusing attention and reducing creativity? And if more workers use it to excel, will we have a workforce of narrow, rigid thinkers?"

Neuroethicists are also worried that these new cognitive technologies could widen the gap between those who can afford them and those who can't, eventually creating different classes of human beings. Just as problematic as unequal access, some say, is the prospect of people being forced, implicitly or explicitly, to take mind-altering medications. Someday we may all feel pressure to take--or give our kids--focus- or memory-sharpening drugs to compete at school or work. In fact, says Richard Glen Boire, senior fellow on law and policy at the Center for Cognitive Liberty & Ethics in Davis, Calif., "some schools require kids--not diagnosed with ADHD by doctors--to take Ritalin to attend school."

Farah also imagines the day when we have what she calls a "neuro-correctional system" that could transform criminals into noncriminals. We already force sex offenders to take libido-dampening drugs or face denial of parole. A drug to dampen violent impulses might someday be similarly applied. That could, in theory, prevent crimes.