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Since its invention over a century ago, the polygraph technique has largely been premised on the theory that lying stimulates the autonomic nervous system (ANS). The autonomic nervous system is a division of the peripheral nervous system (PNS) that controls various involuntary physiological functions.
Notably, the ANS regulates breathing, heart rate, blood pressure, and perspiration. Polygraphs monitor spikes in any of these parameters.
As the autonomic nervous system is a part of the PNS and not the central nervous system (CNS), there have been subtle attempts to downplay the brain’s role in deception and (by extension) polygraph outcomes. However, emerging research suggests otherwise.
Read below as we uncover what neuroscience reveals about polygraph testing and the brain.
What Is Lying?
Lying refers to the conscious, intentional act of engaging in deception. A key thing to note here is that you’re only deemed to be deceptive if you’re aware of your thought process.
That’s to say, liars have a clear perception of reality. They know they should tell the truth, but choose the contrary.
Most people lie to escape the unpleasant consequences of their undesired behaviors. Other common motivations include manipulating high-stakes processes (such as elections and sporting tournaments), protecting one’s reputation, and covering for loved ones.
Regardless of the motivation, undergoing a polygraph test can help uncover reliable hints of deception. Polygraph examiners typically assess significant spikes in respiratory activity, cardiovascular functions, and skin conductivity to infer deception.
Besides, some advanced polygraph machines include motion sensors that measure certain body movements consistent with lying.
What’s The Physiology Behind Lying?
The autonomic nervous system has two major divisions involved in regulating involuntary activities. They include the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS).
The ANS, through its sympathetic system, controls the body’s “fight-or-flight” response.
Fight-or-flight is the body’s reaction during extremely stressful moments. It’s essentially what causes us to confront or flee from potentially life-threatening situations.
Now, lying arouses the ANS’ sympathetic nervous system by exerting emotional stress on the body. The body responds by releasing a rush of adrenaline.
High adrenaline levels cause a surge in blood pressure, pulse rate, respiration, and perspiration. This happens as the body marshals every weapon in its defense arsenal to combat the imminent threat.
An increase in cardiovascular activity ramps up the supply of oxygen and essential nutrients to the brain. The brain needs to be well-nourished to remain alert in perceived danger.
Similarly, a spike in respiration causes you to inhale more oxygen with each breath. Perspiration rate increases to cool the body as it deals effectively with the threat.
When you take a polygraph test, an examiner will attach various sensors to capture relevant biofeedback.
Pneumographs go to the upper and lower torso, helping to track respiratory activity. Sphygmographs measure changes in pulse rate and blood pressure, while galvanographs monitor changes in skin conductivity due to increased sweating.
At the end of a lie detector test, an examiner interprets these datasets to infer honesty or deception.
What’s The Psychology Behind Lying?
While lying may appear to be solely a domain of the autonomic nervous system, the brain plays an instrumental role, too.
Right before telling a lie, we already have a perception of truth. But instead of impressing our brains to retrieve factual information, we compel it to concoct a falsehood.
Various parts of the brain play a part in processing deception. However, the prefrontal cortex is the most involved.
Previous brain scans have shown that deception triggers the dorsolateral prefrontal cortex (DLPFC) and the right middle frontal gyrus. These are the core areas of the prefrontal cortex involved in critical decision-making, emotional regulation, and self-control.
Other regions of the brain impacted by lying include the;
- Hippocampus – Responsible for storing and retrieving episodic memories
- Anterior Cingulate Cortex – Evaluates emotional conflicts between honest and deceptive responses
Note that it’s easier to fetch the truth from our memory than suppress it. As lying exerts undue cognitive load on the brain, it’s difficult to go unnoticed.
Relationship Between Neuroscience and Polygraphs
Neuroscientists and psychologists can rely on certain behavioral cues to infer deception, such as fidgeting, gaze shifting, defensive postures, and tonal variations.
Like the physiological metrics that polygraph machines measure, these reactions are often spontaneous. That’s because the brain is more fixated on sustaining a lie than controlling other bodily functions.
Besides, studies have shown that the autonomic nervous system may aid certain cognitive functions like attention and memory. This intersection lends further evidence to the role of both the brain and ANS in supporting truth suppression.
Last but not least, both neuroscience and polygraphs utilize similar investigation techniques. One such methodology is the Concealed Information Test (CIT).
In polygraphs, a CIT test involves posing several relevant questions to assess an examinee’s recognition of intimate crime-related facts.
Patterns of significant arousal indicate an individual either witnessed the incident under investigation or had a significant part in it. They can then be pressed further on their actual role in the crime.
However, CIT questions should be presented objectively and not in an accusatory tone.
Summary
Polygraphs track changes in the four key ANS-regulated functions, enabling examiners to interpret spikes in these parameters as evidence of deception.
However, modern polygraphy isn’t only rooted in physiology. It addresses fundamental psychological aspects, too. By analyzing the body’s involuntary responses to lying, lie detector tests can provide a critical glimpse into how the brain processes deception.
*This article is based on personal suggestions and/or experiences and is for informational purposes only. This should not be used as professional advice. Please consult a professional where applicable.