Technology can be seductive because it provides an instant reward - a text message from a friend, success in a video game or stimulating news on a Web site - that is not necessarily harmful.
But mental health experts say an addiction can form - just as with gambling - when people keep seeking that intermittent, unpredictable reward.
"The fact that it is unpredictable is what compels the brain to keep checking over and over and over," said Dr. David Greenfield, assistant clinical professor of psychiatry at the University of Connecticut School of Medicine.
"When people are afraid of not having their PDA or a phone with them, then it's addictive," Greenfield said.
Still, the question is: When does an addiction to technology become a problem?
Human contact suffersDr. Kimberly Young, founder and director of the Center for Internet Addiction Recovery of Bradford, Pa., said it depends on individual circumstances.
"It's not a time limit," said Young, who has been studying Internet addiction since 1994. "You can't diagnose alcoholism by how much someone drinks. "
Also, she said, "it's a generational thing. Go interview a 15-year-old, a 45-year-old and a 75-year-old, and you'll have different views of technology. For 15-year-olds, it's their lifeline."
But some of the warning signs include being so preoccupied with online activities that it affects relationships. (For more on signs of addiction, see the chart on the next page.)
There's a problem with "someone who is always having to get up in the middle of the night to check e-mail and not having sex with his wife," she said.
According to the center's Web site, NetAddiction.com, the most common type of Internet addiction is online pornography, but online gambling, auction sites and multiplayer role playing games are also on the rise. Surveys indicate half of Internet addicts also have another addiction, such as drugs, alcohol, smoking or sex.
Brain chemistryDr. John Ratey, an associate clinical professor of psychiatry at Harvard Medical School, said a physical addiction can form from the chemical reaction in the brain - a "dopamine squirt" - that comes from a rewarding tech experience.
"We condition ourselves to need it, and after a while, it becomes a physical need like any other constant practice," Ratey said. "It's worse now because we've got all these devices."
Greenfield said that 10 years ago there used to be more debate among mental health professionals about whether Internet addiction was an actual malady or a symptom of more recognized problems such as depression and social isolation.
In fact, a Pew Research Center study released last month concluded that the rise of Internet and mobile phone use has not made Americans more socially isolated.
"Personally, I have some doubts about the notion that there can be an Internet addiction," said sociologist Keith Hampton, the Pew study's lead author and an assistant professor at the Annenberg School for Communication at the University of Pennsylvania.
"We can't forget that we had media before the Internet," he said. "Husbands have been sitting at the dinner table reading the newspaper for a long time. Just because the devices change doesn't necessarily mean that the overall social pattern has changed."
China's responseAround the world, however, experts say they are just starting to measure the effects.
In China, which has almost 300 million Internet users, the government has declared Internet and video game addiction a public health problem.
Studies have found anywhere from 2.4 to 15 percent have a problematic Internet addiction, said Dr. Cheng-Hua Tian, professor of psychiatry at the Peking University Institute of Mental Health. In an e-mail, Tian said he and other senior psychiatrists are developing diagnostic criteria to more accurately measure addiction, which affects teenagers more than adults.
In the United States, Greenfield said, studies have estimated anywhere from 3 to 6 percent of Internet users have a problem. The nation's first inpatient "detox" center focusing on Internet and video game addiction opened in Fall City, Wash., in July.
The reStart Internet Addiction Recovery Clinic, which charges $14,000 for a 45-day recovery program, has treated three men and one woman who sought to kick serious video game habits that left them unable to complete school or hindered their ability to form real-world relationships, said clinic co-founder Dr. Hilarie Cash.
Instant gratificationIn serious cases, technology "can be more immediately gratifying than the labor of building an intimate relationship," Cash said. "That is one of the biggest prices we pay by letting ourselves get seduced by all this technology."
Dr. Elias Aboujaoude, assistant director of the Stanford School of Medicine's Obsessive-Compulsive Disorder Clinic, said there's no question in his mind that technology can cause problem addictions.
"From a clinical experience, I've seen plenty of people whose primary problem is an Internet problem," he said. "They're not gamblers, they're not pornography addicts, they're not necessarily depressed. And there are real offline consequences that we are just starting to appreciate.
"What we're seeing is that people with social anxiety are gravitating online as a substitute, and that can be OK to a certain point," he said. "There's nothing wrong with having these connections, unless your real-life relationships begin to suffer, and that's when it becomes problematic. Some of them truly have difficulty forming real-life relationships."
Signs of addictionHere are some questions to ask if you think you are addicted to the Internet:
-- Do you spend excessive time online, or more than you intended?
-- Do you feel more depressed or lonely the more time you spend online?
-- Do you have a heightened sense of euphoria while online or using a computer?
-- Is it interfering with your job or school performance?
-- Do family or friends complain about the time and energy you spend online?
-- Do you frequently chose spending time online over going out with other people?
-- Do you hide, lie or become defensive about online activities?
-- Do you feel depressed, restless, moody or nervous offline and fine again when online?
-- Do you spend too much time with online pornography, multiplayer games or gambling sites?
What to do?Unplug yourself completely from technology for at least a few moments each day.
-- Keep track of how much you use technology, and moderate overuse.
-- If needed, seek counseling, self-help or support groups.
Sources: Virtual-Addiction.com; NetAddiction.com; netaddictionrecovery.com; Dr. John Ratey, Harvard Medical School.