The Physiology of a Lie

Have you ever played an April Fools’ Day prank on someone? Maybe your heart was racing, your hands were clammy, and your breathing was fast as you eagerly watched them discover the trick you so cleverly planned out, waiting for just the right moment to yell: “April Fools’!” Here, we examine the custom as well as the physiological effects of trickery — or lying — on the human body.

How did the April Fools’ Day tradition begin?

The exact history of April Fools’ Day, sometimes called All Fools’ Day, seems unknown. A prevalent theory is that it started in France in 1582, when Pope Gregory XIII signed an edict that moved the country away from using the Julian Calendar — whose New Year coincided roughly with the spring equinox in late March/early April — to using the Gregorian Calendar, with the New Year starting on Jan. 1. Those slow to make the switch were still celebrating the New Year around April 1, while the rest of the country looked at these “April Fools” as being out-of-touch and treated them as the objects of ridicule. Other theories about the origin point to an ancient Roman festival (Hilaria) that roughly coincided with the spring equinox and involved dressing in disguise, engaging in games and amusements, and indulging in general revelry. No matter the true root of April Fool’s Day, people enjoyed the idea of pranking their friends, family, and neighbors enough to continue the tradition throughout the world today.

From placing a whoopee cushion on your boss’s chair (not recommended) to changing your kids’ alarm clock so they think it’s an hour later than it actually is, April Fools’ Day fun involves tricking people into believing something that is not true (that their chair is safe to sit on or that they are late for school). In other words, it involves lying.

What is the truth about how lying affects the body?

What exactly is going on in your body as you watch someone reach for the sugar bowl you’ve clandestinely filled with salt? What about when you tell a friend you’re too busy to hang out, even though you have nothing planned? Or call out sick from work and then spend the day going on a picnic, instead?

For your body, the act of not telling the truth can trigger the body’s fight/flight response, also called the acute stress response. This stress response is regulated by the autonomic nervous system (ANS). The ANS is part of your body’s peripheral nervous system and includes everything in the nervous system aside from the brain and spinal cord, which are part of the central nervous system (CNS). The ANS is responsible for subconsciously maintaining, monitoring, and controlling our internal bodily functions including heart rate, blood vessel diameter, smooth muscle surrounding the organs, and glandular secretions.

The ANS is broken down into sympathetic and parasympathetic nervous systems. In times of stress, like when you are not telling the truth, the sympathetic nervous system gets stimulated.

This results in activating the preganglionic motor cell body (the first motor neuron in the CNS), which receives stress signals from the autonomic sensory neuron. The preganglionic motor neuron then conveys information from the CNS to an autonomic ganglion (a collection of cell bodies of second motor neurons, otherwise known as postganglionic motor neurons) via a cranial or spinal nerve. The preganglionic motor neuron transmits impulses to the postganglionic motor neuron via synapses within the autonomic ganglion, and the impulses get passed via the postganglionic motor fibers to the targeted organs.

What does this all mean for the body? A host of anatomical and physiological changes may occur, and the bigger the lie the more likelihood of a physical reaction to it (think “The Tell-Tale Heart” by Edgar Allan Poe). The “fight/flight” reaction may cause:

1. • Pupil dilation and eye lens adaptation for long vision

1. • Increased blood circulation as the heart rate rises

1. • Lung dilation, allowing for increased respiration

1. • Increased blood sugar levels as the liver and pancreas convert glycogen into glucose for energy

1. • Slowing or ceasing of digestion and urination in order to conserve energy

1. • Excretion of the “fight or flight” hormones epinephrine and norepinephrine by the suprarenal glands

What are the effects of long-term lying?

While we may pull a prank on April Fools’ Day or tell the occasional white lie to spare someone’s feelings, it is worth nothing that repeated and habitual lying can have serious consequences.

Some people habitually lie about anything and everything, known as “pseudologia fantastica”, or pathological lying. This type of lying is often seen in certain types of mental disorders, including anti-social personality disorder (ASPD).

Lying erodes the trust upon which interpersonal relationships are built, can lead to trouble with the law, and can blur the lines between fact and fiction. Research (and history) has shown that the more times you hear a falsehood repeated, the less able you are to discern that it is a lie — even if you have prior knowledge to the contrary. In other words, even though we may know it to be false, it sounds more true. Psychologists call this the “illusion of truth.” Furthermore, studies have also shown that people can be taught to lie more effectively.

What does this mean? Playing a trick on April Fools’ Day can be all fun and games, but when it comes to more serious things that can potentially endanger people it’s crucial to think critically. Instead of just repeating what you’ve heard, look for a reliable source of information that can either back it up or refute it.