Say "truth serum", and what probably comes to mind is comic book villains being interrogated. But yesterday a judge approved use of "narcoanalytic drugs" in the trial of James Holmes ? charged with killing 12 and wounding 58 people at a cinema screening of The Dark Knight Rises in Aurora, Colorado, in July last year.
On Tuesday, Judge William Sylvester entered a not guilty plea on behalf of Holmes, whose lawyers say is not yet ready to enter one himself. Holmes will be allowed to change his plea to not guilty by reason of insanity at a later date. If he does, he will be examined at the Colorado state mental hospital in Pueblo. To be found not guilty by reason of insanity, it must be demonstrated that Holmes did not know right from wrong at the time of the shootings. The judge ruled that "medically appropriate" drugs could be used in this evaluation.
It is not clear what drugs might be used, but one candidate is sodium pentothal. It is a barbiturate that can calm anxiety, induce general anaesthesia and in some US states is given as part of the lethal injection used to administer the death penalty. But can it make you tell the truth? Psychologists and researchers in lie detection contacted by New Scientist seem doubtful.
Like being drunk
"Standard truth serums like sodium pentothal work by inhibiting executive regions of the brain and thereby reducing one's inhibitions to answer questions," says Paul Zak at Claremont Graduate University in California. But it is not clear whether those answers will be accurate, he says, and they can also lack detail. "Under barbiturates, people often engage in fantasy and have delusions. This is similar to someone who is drunk. How much do you trust the story the drunk in the pub tells you?"
Aldert Vrij at the University of Portsmouth, UK, who researches lie detection, says that the judge's ruling is unusual. "I am not aware of any scientific support for truth serums," he says. "Neither am I aware that it has value on determining whether someone is legally insane."
Another drug, oxytocin
, has been called the "trust hormone" since it makes you more cooperative. For this reason, it has also been touted as a potential interrogation drug.
Markus Heinrichs at the University of Freiburg, Germany, who has studied oxytocin's influence on behaviour, says that oxytocin increases interpersonal trust and empathy without affecting general rational decisions, but it is not a truth serum. "Oxytocin is definitely not suitable for this purpose."
Violation of rights?
The possible use of truth drugs is a surprising development in the Holmes trial, says Jason Odeshoo at law firm Jenner & Block in Chicago, Illinois. He says the value of such drugs in this particular case is unclear. "Regardless of their effectiveness, administering truth serums arguably violates an individual's rights under the US constitution," he says. "However, the constitutional implications of using a truth serum to test an insanity plea are less clear."
Some countries still use truth serums regularly in criminal investigations. In India, for example, such a drug was reportedly used to obtain a confession from Mohammed Ajmal Amir Kasab ? convicted of involvement in the 2008 bombing and shooting attacks across Mumbai in India, and later executed.
Holmes may also face a polygraph test that is supposed to detect lying. The test monitors signals such as heart rate and respiration, but as with truth serums, its validity is widely disputed.
Limited studies
"It's possible that the polygraph, using physiological signals such as skin conductance to detect deception, may be useful, but there are hurdles that need to be overcome," says Brian Bell at the University of Nottingham, UK. For example, there are only very limited studies of how lie detection tests may be affected by the subject's age, intelligence, mental health and ability to use tricks to fool the machine.
Bell has investigated how fMRI scans can supplement physiological signals in detecting deception. There are already commercial lie-detection tests that use brain scanning throughout the US. The earliest such test was used in a much-reported case in 2003, when Joel Huizenga of No Lie MRI used fMRI to scan the brain of Harvey Nathan. Nathan had made an insurance claim after his business in Charleston, South Carolina, burned down, but his insurers said he had started the fire himself. The evidence that No Lie MRI provided supported Nathan's version of events, but it is unclear whether the insurance company accepted it and paid up.
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