HOUSTON -- Sophisticated magnetic resonance scanning equipment is being employed at the Baylor College of Medicine to answer age-old questions about how the human brain reacts to stimuli and formulates decisions. Like which is better, Coke or Pepsi?

As a man's head is scanned every two seconds by an 8,800-pound functional MRI at the Baylor College of Medicine's Human Neuroimaging Laboratory, the subject sees flashes of cola cans followed by short squirts of soda _ either Coke or Pepsi _ for 25 minutes. Researchers then will go over the data and determine how his brain reacted to each dose.

So far, neuroimaging on subjects not told which brand they were drinking has indicated that Pepsi generally elicited more activity in parts of the brain that indicate pleasure, regardless of the taster's stated preference.

"They subjectively disagree with what their behavior says," Dr. Read Montague said during a tour of his lab Tuesday, adding that positive feelings about branding of products such as Coke can outweigh actual taste of the product itself, which he said explains why the 1980s rollout of "New Coke" was such a failure.

Of course, the 6-month-old lab is more than a $9 million version of the Pepsi Challenge. The smartly furnished, airy offices are devoted to research on human brains in a variety of social interactions, such as trust between two individuals, mother-infant attachment and decision-making under pressure.

Subjects are fed information through video screens or interact with one another via the Internet in similar MRI tubes at Cal Tech, Emory University in Atlanta and Princeton University in New Jersey. The simultaneous research linking patients thousands of miles apart, called hyperscanning, allows scientists to pool expensive resources.

"Research involving brain responses during social interactions has a broad impact on society, ranging from influencing current social policy to the treatment of mental illness," said Montague, director of the Human Neuroimaging Laboratory and a neuroscience professor at Baylor.

Though the lab has measured activity in sick brains, such as those in Parkinson's patients, Montague reserves the lab for the study of healthy brains to fulfill its mission to understand the biological nature of how everyday reactions happen.

"In order to understand how the brain controls behavior, you have to understand the brain," said Dr. James Patrick, who built the neuroscience division at Baylor.

One fact researchers are studying is the nature of human decision-making. Are we the masters of our own minds or are most of the things we do and think predetermined by neurons working on autopilot?

"All of us believe we control all of our decision-making," Montague said. "One of the things I suspect will come out of this is whether or not that is true."

Down the road, doctors and social workers using data that soon will be compiled on teen mothers responses toward their babies might better learn how to boost maternal empathy, perhaps improving the lives of the children, Montague said.

The complex interdisciplinary relationships among the computer scientists, physicists, mathematicians, neuroscientists, psychologists, psychiatrists and others that work in the lab can be confusing at times _ "It's like one person speaking Chinese and another person speaking Finnish," noted Montague _ but he says it's the key to producing research.

"No (one person) knows how to analyze all this data. We make it up as we go sometimes," he said. "We really are on the leading edge."