How do lie detectors work?

Experts explain how lie detectors work, what happens in the brain when we tell lies and how accurate polygraph tests are.

lie detector test
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  • In a 2002 study, 60 percent of people were found to lie at least once during a 10-minute conversation, with most people telling an average of two or three lies. The polygraph, invented in the early 1920s, detects physiological responses to lying (such as elevated heart and respiratory rates as well as spikes in blood pressure.
  • Three main areas of the brain are stimulated during deception: the frontal lobe, the limbic system, and the temporal lobe.
  • According to the American Polygraph Association, the estimated accuracy of a polygraph can be up to 87 percent.

What happens in your brain when you lie?

concept of lying polygraph test

Image by Shidlovski on Shutterstock

We all lie. Some might argue it's human nature. In a 2002 study, 60 percent of people were found to lie at least once during a 10-minute conversation, with most people telling an average of two or three lies. Some lies are small, some are bigger, some are done out of kindness, and some done out of malice. But a lie is a lie, and the way that your body reacts when you lie is the same.

Lying is an inherently stressful activity.

When you engage in a false narrative (or a lie), your respiratory and heart rate will increase and you may even start to sweat. While people may vary in the ability to tell a lie, most of the time your body will react in this same way. Exceptions to this rule are, for example, psychopaths, who lack empathy and therefore do not exhibit the typical physiological stress responses when telling a lie.

Brain imaging studies have shown what really happens in the brain when you tell a lie.

Lying generally involves more effort than telling the truth, and because of this, it involves the prefrontal cortex. A 2001 study by late neuroscientist Sean Spence (University of Sheffield in England) explored fMRI images of the brain while lying. Participants answered questions about their daily routine by pressing a yes or no button on a screen. Depending on the color of the writing, they were to answer either truthfully or with a lie.

The results showed participants needed more time to formulate a dishonest answer than an honest one, and certain parts of the prefrontal cortex were more active when they were lying.

Further research explains that three main areas of the brain are stimulated during deception - the frontal lobe works to suppress the truth, the limbic system activates due to the anxiety that comes from lying, and the temporal lobe activates in response to retrieving memories and creating mental imagery (fabricating a believable lie).

Research also suggests lying becomes easier the more you do it.

In a 2016 study, Duke psychologist Dan Ariely and his colleagues showed how dishonesty can alter your brain, making it easier to tell lies in the future. When people told lies, the scientists noticed a burst of activity in the amygdala, the part of the brain involved in fear, anxiety, and emotional responses. When the scientists had their subject play a game in which they won money by deceiving their partner, they noticed the negative signals from the amygdala begin to decrease.

"Lying, in fact, desensitized your brain to the fear of getting caught of hurting others, making lying for your own benefit down the road much easier," wrote Jessica Stillman for INC.

How do lie detectors work?

lie detector illustration

The polygraph will be able to detect if someone is telling the truth 87 percent of the time.

Image by OllivsArt on Shutterstock

In 1921, a California-based police officer and physiologist John A. Larson created an apparatus that simultaneously measures continuous changes in blood pressure, heart rate, and respiration rate to aid in the detection of deception. This was the invention of the polygraph, which is commonly referred to as a lie detector.

Seven years before this, in 1914, an Italian psychologist (Vittorio Benussi) published findings on "the respiratory symptoms of a lie," and in 1915, an American psychologist and lawyer (William M. Marston) invented a blood pressure test for the detection of deception.

The accuracy of polygraph tests has been called into question for nearly as long as they've existed. These machines detect typical stress responses to telling a lie. This means increased heart rate, blood pressure, and respiration rate. Some people are naturally good liars, or become better with controlling these stress responses, and can manage to stay calm during a lie detector test.

According to the American Polygraph Association (made up largely of polygraph examiners), the estimated accuracy of a polygraph can be up to 87 percent. That means that in 87 out of 100 cases, the polygraph will be able to detect if someone is telling the truth.

If the person lies but doesn't have the stress symptoms of telling that lie, they will pass the test. Similarly, innocent people may fail the test due to being anxious about taking it to begin with and therefore emitting the elevated heart, respiratory, and blood pressure rates that can be detected.

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CRISPR therapy cures first genetic disorder inside the body

It marks a breakthrough in using gene editing to treat diseases.

Credit: National Cancer Institute via Unsplash
Technology & Innovation

This article was originally published by our sister site, Freethink.

For the first time, researchers appear to have effectively treated a genetic disorder by directly injecting a CRISPR therapy into patients' bloodstreams — overcoming one of the biggest hurdles to curing diseases with the gene editing technology.

The therapy appears to be astonishingly effective, editing nearly every cell in the liver to stop a disease-causing mutation.

The challenge: CRISPR gives us the ability to correct genetic mutations, and given that such mutations are responsible for more than 6,000 human diseases, the tech has the potential to dramatically improve human health.

One way to use CRISPR to treat diseases is to remove affected cells from a patient, edit out the mutation in the lab, and place the cells back in the body to replicate — that's how one team functionally cured people with the blood disorder sickle cell anemia, editing and then infusing bone marrow cells.

Bone marrow is a special case, though, and many mutations cause disease in organs that are harder to fix.

Another option is to insert the CRISPR system itself into the body so that it can make edits directly in the affected organs (that's only been attempted once, in an ongoing study in which people had a CRISPR therapy injected into their eyes to treat a rare vision disorder).

Injecting a CRISPR therapy right into the bloodstream has been a problem, though, because the therapy has to find the right cells to edit. An inherited mutation will be in the DNA of every cell of your body, but if it only causes disease in the liver, you don't want your therapy being used up in the pancreas or kidneys.

A new CRISPR therapy: Now, researchers from Intellia Therapeutics and Regeneron Pharmaceuticals have demonstrated for the first time that a CRISPR therapy delivered into the bloodstream can travel to desired tissues to make edits.

We can overcome one of the biggest challenges with applying CRISPR clinically.

—JENNIFER DOUDNA

"This is a major milestone for patients," Jennifer Doudna, co-developer of CRISPR, who wasn't involved in the trial, told NPR.

"While these are early data, they show us that we can overcome one of the biggest challenges with applying CRISPR clinically so far, which is being able to deliver it systemically and get it to the right place," she continued.

What they did: During a phase 1 clinical trial, Intellia researchers injected a CRISPR therapy dubbed NTLA-2001 into the bloodstreams of six people with a rare, potentially fatal genetic disorder called transthyretin amyloidosis.

The livers of people with transthyretin amyloidosis produce a destructive protein, and the CRISPR therapy was designed to target the gene that makes the protein and halt its production. After just one injection of NTLA-2001, the three patients given a higher dose saw their levels of the protein drop by 80% to 96%.

A better option: The CRISPR therapy produced only mild adverse effects and did lower the protein levels, but we don't know yet if the effect will be permanent. It'll also be a few months before we know if the therapy can alleviate the symptoms of transthyretin amyloidosis.

This is a wonderful day for the future of gene-editing as a medicine.

—FYODOR URNOV

If everything goes as hoped, though, NTLA-2001 could one day offer a better treatment option for transthyretin amyloidosis than a currently approved medication, patisiran, which only reduces toxic protein levels by 81% and must be injected regularly.

Looking ahead: Even more exciting than NTLA-2001's potential impact on transthyretin amyloidosis, though, is the knowledge that we may be able to use CRISPR injections to treat other genetic disorders that are difficult to target directly, such as heart or brain diseases.

"This is a wonderful day for the future of gene-editing as a medicine," Fyodor Urnov, a UC Berkeley professor of genetics, who wasn't involved in the trial, told NPR. "We as a species are watching this remarkable new show called: our gene-edited future."

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