A recent polygraph test taken in Orange County, Calif., has brought the validity of polygraphs — also called "lie detector tests" — into question.

Even though some police departments and counterintelligence units use them, generally, results of such tests aren't admissible in court. So, what does the research say?

Though polygraph-type machines have existed in some form since the late 1800s, the machines, which detect micro changes in a person's bodily functions, came to popularity in the 1920s and '30s, according to research out of Harvard's Countway Library. Modern polygraphs record bodily changes like respiration, blood pressure and sweat gland activity, which many believe are said to reveal stress and/or deception.

But even though today's polygraphs are more advanced, the science behind them has still yet to be proven effectively enough and many experts consider the practice

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