Advocates often portray torture, like waterboarding, as black magic that quickly enables the interrogator to break through his subject’s defenses and force him to divulge the location of the bomb that will destroy Los Angeles. But what does the scientific literature say? A 2006 Intelligence Science Board flatly noted that there was no data supporting the claim that torture produces reliable results. The 372-page report would be summed up by this passage: “The scientific community has never established that coercive interrogation methods are an effective means of obtaining reliable intelligence information. In essence, there seems to be an unsubstantiated assumption that ‘compliance’ carries the same connotation as ‘meaningful cooperation.’ ” In other words, waterboard someone or smack his head against the wall, and sure enough, he’ll open up and talk. But does that mean you’ll get reliable info that you couldn’t have gotten using more conventional techniques? Absolutely not. Dick Cheney insisted that two CIA analytical reports (that he apparently pressed to have prepared) concluded that his torture techniques rendered positive results. But these reports were declassified and published, and lo, they don’t say what he claimed they do.

Now another important contribution to the scientific literature has appeared. Irish neurobiologist Shane O’Mara of Trinity College Dublin, writing in Trends in Cognitive Sciences, takes a special look at the Bush Administration’s enhanced interrogation techniques:

the use of such techniques appears motivated by a folk psychology that is demonstrably incorrect. Solid scientific evidence on how repeated and extreme stress and pain affect memory and executive functions (such as planning or forming intentions) suggests these techniques are unlikely to do anything other than the opposite of that intended by coercive or ‘enhanced’ interrogation.

Newsweek’s Sharon Begley summarizes O’Mara’s analysis:

So let’s break this down anatomically. Fact One: To recall information stored in the brain, you must activate a number of areas, especially the prefrontal cortex (site of intentionality) and hippocampus (the door to long-term memory storage). Fact Two: Stress such as that caused by torture releases the hormone cortisol, which can impair cognitive function, including that of the prefrontal cortex and hippocampus. Studies in which soldiers were subjected to stress in the form of food and sleep deprivation have found that it impaired their ability to recall personal memories and information, as this 2006 study reported. “Studies of extreme stress with Special Forces Soldiers have found that recall of previously-learned information was impaired after stress occurred,” notes O’Mara. “Water-boarding in particular is an extreme stressor and has the potential to elicit widespread stress-induced changes in the brain.”

Stress also releases catecholamines such as noradrenaline, which can enlarge the amygdale (structures involved in the processing of fear), also impairing memory and the ability to distinguish a true memory from a false or implanted one. Brain imaging of torture victims, as in this study, suggest why: torture triggers abnormal patterns of activation in the frontal and temporal lobes, impairing memory. Rather than a question triggering a (relatively) simple pattern of brain activation that leads to the stored memory of information that can answer the question, the question stimulates memories almost chaotically, without regard to their truthfulness. These neurochemical effects set the stage for two serious pitfalls of interrogation under torture, argues O’Mara. The first is that “information presented by the captor to elicit responses during interrogation may inadvertently become part of the suspect’s memory, especially since suspects are under extreme stress and are required to tell and retell the same events which may have happened over a period of years.” As a result, information produced by the suspect may parrot or embellish suggestions from the interrogators rather than revealing something both truthful and unknown to the interrogators. Second, cortisol-induced damage to the prefrontal cortex can cause confabulation, or false memories. Because a person being tortured loses the ability to distinguish between true and false memories, as a 2008 study showed, further pain and stress does not cause him to tell the truth, but to retreat further into a fog where he cannot tell true from false.

There is another factor that casts doubt on the reliability of statements made by a torture subject. O’Mara puts it simply: “while I’m talking, I’m not being water-boarded.” It’s a sort of Pavlovian conditioning—if I talk, the torture will stop. Such circumstances virtually guarantee that a subject will talk. They just don’t make it more likely that he will tell the truth. In fact, just the opposite. “To briefly summarize a vast, complex literature: prolonged and extreme stress inhibits the biological processes believed to support memory in the brain,” writes the Irish scholar. “Coercive interrogations involving extreme stress are unlikely, given our current cognitive neurobiological knowledge, to facilitate the release of veridical information from long-term memory.” Let’s translate that: torture tends to make the information provided less reliable.