What happens when you tell a lie? Set aside your ethical concerns for a moment -- after all, lying is a habit we practice with astonishing dexterity and frequency, whether we realize it or not. What goes on in your brain when you willfully deceive someone? And what happens later, when you attempt to access the memory of your deceit? How you remember a lie may be impacted profoundly by how you lie, according to a new study by LSU Associate Professor Sean Lane and former graduate student Kathleen Vieria.

The study, accepted for publication in the Journal of Applied Research and Memory Cognition, examines two kinds of lies -- false descriptions and false denials -- and the different cognitive machinery that we use to record and retrieve them.

False descriptions are deliberate flights of the imagination -- details and descriptions that we invent for something that didn't happen. As it turned out, these lies were far easier for Lane's test subjects to remember.

Lane explained that false descriptions remain more accessible and more durable in our memories because they tax our cognitive power.

"If I'm going to lie to you about something that didn't happen, I'm going to have to keep a lot of different constraints in mind," Lane said.

Liars must remember what they say, and also monitor how plausible they seem, the depth of detail they offer, even how confident they appear to the listener. And if the listener doesn't seem to be buying it, they must adapt the story accordingly.

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"As the constructive process lays down records of our details and descriptions, it also lays down information about the process of construction," Lane said.

In short, false descriptions take work. We remember them well precisely because of the effort required to make them up. When subjects in Lane's study were asked to recall their own false descriptions 48 hours later, their memories were largely accurate. They remembered what they said, and they remembered that what they said was inaccurate.

The same is not true for false denials. This kind of lie -- denying something that actually happened -- is often brief, and its cognitive demand is therefore much smaller.

With a false denial, Lane said, "I'm not constructing details. But I'm also not going to remember the act because there's not much cognitively involved in the denial." Lane's test subjects had a hard time remembering their own false denials after 48 hours.

This finding has implications for forensic interrogation, where suspects often encounter a series of rapid-fire questions. A guilty suspect is more inclined to forget a false denial, and therefore more likely to contradict himself on the same information later.

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But there is a haunting implication for innocent suspects, too. Lane's test subjects also had a hard time remembering if the denials they'd made were true or false. This same memory problem might plague suspects who are asked to make repeated truthful denials.

To explain, Lane cited the "illusory truth effect," the idea that hearing false information repeatedly will make it seem truthful, simply because it's familiar. His study takes this idea in a new direction.

"They're telling the truth, they're denying, but later this thing seems familiar," said Lane. "They're confusing the familiarity of the repetition [with the truth], not realizing that those repeated denials are what makes it seem familiar 48 hours later."

This means that telling the truth can actually lead to a false memory. A man who repeatedly denies being present at the scene of the crime, for example, might actually begin to imagine that scene -- where it was, what it looked like, who was present -- even if he was never there. It feels strangely familiar to him, and because the repeated denials have slipped from his memory, he can't explain why.

False memory is a well-documented phenomenon, and Lane has researched it extensively throughout his career. In a courtroom, it can be disastrous. Through studies like this one, Lane offers forensic investigators a deeper insight into this bizarre behavior.