Researchers from the University of Chicago reported in 2004 that babies who fall to sudden infant death syndrome appear to have deficits of a brain chemical called serotonin in the areas that control breathing.

These deficits leave them unable to gasp, or recover, from a sudden drop in blood pressure that can be a SIDS trigger, according to breathing researcher Dr. Ronald Harper of the University of California at Los Angeles.

"We believe that something has gone wrong with these infants even in fetal life," he said. "And there's an overwhelming body of evidence to support that issue that these infants are somehow unable to respond to blood pressure challenges."

Whatever the trigger for the sudden blood pressure drop, it is the inability of the infant's body to respond properly that is fatal, he said.

"The net result is they go into a kind of shock-like reaction.

The ability to gasp not only helps restore breathing, but also boosts blood pressure and gets oxygen circulating again, he said.

The Chicago team of researchers, who published their findings in the journal Neuron, hope to some day find a method or test that would be able to alert parents to serotonin deficits in their infants that might put them at risk for SIDS.