Perhaps the problem with creating machines to spot falsehoods is rooted in the very nature of lies. Scientists who have examined lies per se have found that different types activate different parts of the brain; not all lies are psychologically similar. In their seminal studies, psychologists Stephen Kosslyn and Giorgio Ganis focused on two types of lies: spontaneous lies and rehearsed, or memorized, lies. The latter, as the name implies, are those you are prepared to tell when your friend asks you if you are sticking to your diet. A prepared answer might be “I had a tiny salad” when the truth is that you had a burger and fries. Spontaneous lies are those you tell on the fly, as when your friend asks you whether you can give her annoying boyfriend a ride to the airport, and you say you can’t do it because your car is in the shop.
Kosslyn and Ganis hypothesized that when people tell rehearsed lies, they merely need to retrieve them from memory. A spontaneous lie, by contrast, takes more work. When your friend asks you to chauffeur her boyfriend, you must engage episodic memory (responsible for recalling events), such as your past dealings with the boyfriend, and semantic memory (responsible for recalling knowledge) to help manufacture the lie. Presumably, a spontaneous lie would be richer in detail, too, involving visual images or feelings that are encoded in various parts of the brain and thereby giving rise to a more complicated neural representation.
In their experiment, the researchers asked subjects to describe two experiences: their best job and their most memorable vacation. They asked the subjects to choose one of the two experiences, the job or the vacation, whichever they preferred, and to create an alternative version of it and memorize it. So, if the actual vacation was “My parents and I flew from Boston to Barcelona on Continental Airlines and stayed at the Granvia Hotel,” the altered version might be “My sister and I drove from Los Angeles to Mexico City and stayed in a hostel.” A student memorized the false version for about a week and returned to the lab to be scanned. During the scan, researchers told each student to make up some new (spontaneous) untruths on the fly. So subjects would lie on the spot when asked where they went on vacation and replace Mexico City with, say, Miami or respond “my aunt” when asked who their travel companion was. A parallel scenario was tested for the best job one ever had if students chose that option.
As the researchers predicted, different brain networks were engaged during spontaneous lying than during rehearsed lying, and both differ from those used during truth telling. Both involve memory processing, but when subjects lied spontaneously, their brains drew more heavily on the anterior cingulate cortex, which presumably facilitated the suppression of what otherwise would have been a truthful response. When their lies were rehearsed, a region in the right anterior prefrontal cortex (involved in retrieving episodic memory) was selectively activated. Truthful memories were the least effortful to produce, presumably because they were acquired naturally and did not require the kind of auditing and editing that spontaneous lies required.
The point is this: No brain region uniquely changes activity when a person lies; each type of lie requires its own set of neural processes. This is because lies are not all alike psychologically. Journalist Margaret Talbot offers a nuanced litany of lies based on motives: “small, polite lies; big, brazen, self- aggrandizing lies; lies to protect or enchant our children; lies that we don’t really acknowledge to ourselves as lies; complicated alibis that we spend days rehearsing.” Some lies are even told for the mere fun of fooling others, a practice psychologists call “duping delight.” And what about the “more-or-less honest omissions, exaggerations, shadings, fudgings, slantings, bendings, and hedgings” that are an omnipresent feature of litigation, one scholar asks?
Montaigne, the 16th-century French Renaissance essayist, reflected on the kaleidoscopic variety of deception: “The reverse side of the truth has a hundred thousand shapes and no defined limits.” Half a millennium later, researchers are beginning to discern some of those shapes. The lies you tell about yourself, for example, look different on brain scans from those you tell about others. A lie about, say, one’s house will rely on quite different cognitive functions than a lie about a future home, which will engage its own patterns of thought, emotion, and imagination. A lie that generates profound remorse won’t overlap fully, if at all, with the neural correlates of a glib fib. A lie about the future will differ in its neural correlates from one about the past. Montaigne was right: From the whitest of lies to the darkest of deceptions, “the reverse side of the truth has no defined limits.”
This essay is excerpted from Brainwashed: The Seductive Appeal of Mindless Neuroscience by Sally Satel and Scott Lilienfeld, out this week from Basic Books. Future Tense is a partnership of Slate, the New America Foundation, and Arizona State University.