Washington ? The world is becoming a trickier place for people who tell lies even little white ones.

From thermal-imaging cameras, designed to read guilty eyes, to brain-wave scanners, which essentially watch a lie in motion, the technology of truth-seeking is leaping forward.

Researcher Dan Langleben says two areas of the brain exhibit increased neuron activity when a person tells even the simplest of lies. When viewing the brain with an MRI scanner, the increased activity appears as bright spots in the premotor cortex on the left side and the anterior cingulate gyrus located near the middle.

At the same time, more people are finding their words put to the test, especially those who work for the government.

FBI agents, themselves subjected to more polygraphs as a result of the Robert Hanssen spy case, have been administering lie detection tests at Fort Detrick, Md., and Dugway Proving Ground in Utah, bases with stores of anthrax. Nuclear plant workers also are getting the tests in greater numbers since Sept. 11.

“There has been a reawakening of our interest in being able to determine the truth from each other,” said sociologist Barbara Hetrick, who teaches a course on lying at the College of Wooster in Ohio. “As technology advances, we may have to decide whether we want to let a machine decide guilt or innocence.”

The new frontiers of lie detection claim to offer greater reliability than the decades-old polygraph, which measures heart and respiratory rates as a person answers questions.

They also pose new privacy problems, moral dilemmas and the possibility that the average person will unwittingly face a test.

At the Mayo Clinic, researchers hope to perfect a heat-sensing camera that could scan people’s faces and find subtle changes associated with lying. In a small study of 20 people, the high-resolution thermal imaging camera detected a faint blushing around the eyes of those who lied.

The technique, still preliminary, could provide a simple and rapid way of scanning people being questioned at airports or border crossings, researchers say.

But would it be legal?

“As long as no one was being arrested or detained solely on the basis of the test, there is no law against scanning someone’s face with a device,” said Justin Hammerstein, a civil liberties attorney in New York.

At the University of Pennsylvania, researcher Daniel Langleben is using a magnetic resonance imaging machine, the device used to detect tumors, to identify parts of the brain that people use when they lie.

“In the brain, you never get something for nothing,” Langleben said. “The process for telling a lie is more complicated than telling the truth, resulting in more neuron activity.”

Even for the smoothest-talker, lying is tough work for the brain.

First, the liar must hear the question and process it. Almost by instinct, a liar will first think of the true answer before devising or speaking an already devised false answer.

All that thinking adds up to a lot of electrical signals shooting back and forth. Langleben says the extra thought makes some sections of the brain light up like a bulb when viewed with an MRI.