Neuroscientists have been using brain scans to learn how to read minds. This research is increasing our basic understanding of the human brain and offering hope for medical breakthroughs. We should all applaud this work. Commercial firms, however, are beginning to apply this research to lie detection, selling their services. The technology is tempting, but before we accept it, we need to think hard about it—and go slow.

The trouble is not with the pace of research. Neuroscientists have been publishing articles about detecting lies with functional magnetic resonance imaging (fMRI) for nearly 10 years. About 25 published studies have found correlations between when experimental subjects were telling a lie and the pattern of blood flow in their brains. The trouble is that different studies, using different methods, have drawn conclusions based on the activity of different brain regions. And all the studies so far have taken place in the artificial environment of the laboratory, using people who knew they were taking part in an experiment and who were following instructions to lie.

None of the studies examined lie detection in real-world situations. No government agency has found that this method works; no independent bodies have tested the approach. Yet people are buying lie-detection reports, wrapped in the glamour of science, to try to prove their honesty. In May two separate cases wound up in the courts.