How Your Lie–Detector Chin Gives Away the Naked Truth

Speak what you want, but what’s on your mind plays out on your face

Posted Feb 20, 2016

Earlier posts on the topic of body language and emotional intelligence explored

YouTube/silver start NY SITI

During the President's meeting with Putin.

Source: YouTube/silver start NY SITI

How could your chin possibly reveal what’s really on your mind? The answer, as usual in counterintuitive scenarios like this, is that emotion plays out strongly on one’s face. That much is obvious: we read others by reading their expressions and gestures, both of which are driven by emotional circuits over which we have little control.

But wait. Politicians can put on a poker face, [1] can’t they? We already know that they are heavily coached by media consultants. They rehearse their talking points or else read from a teleprompter so they don’t veer “off message” and implode. Politicians work overtime to not give straight answers or lose their cool. They evade. They obfuscate. They hedge.

But it is hard to hide one’s true feelings. Former House Speaker John Boehner famously teared up over matters that didn’t move others at all. His affect was labile, meaning easily swung from one extreme to another. The important point is that the emotional display was beyond his control [2].

Politicians’ efforts at self–control fail because each of us has a built-in lie detector—the mirror neurons in our own brain that fire when we watch another face. The emotional networks of sender and receiver resonate with one another; we pick up their vibes just as others pick up ours. This is why complex feelings arise—good or bad—when we engage socially. And if you happen to know where to look, your mind–reading skills will improve.

The chin is an excellent target for lie detection and inferring states of mind. Why? Because the mentalis muscle—1 of our 54 facial muscles—is richly innervated by the involuntary, extrapyramidal motor system (more on that in a moment).

Mentum is the Latin anatomical term for “chin.” The mentalis muscle at its tip lies just beneath the skin. Contracting it makes the chin dimple like an orange peel. Practice in front of a mirror and you can learn to contract it at will. But this effortful influence is insignificant compared to the sway of emotionally–mediated nerve fibers.

One elicits a “mental reflex” in clinical neurology, a contraction of the mentalis muscle, by stroking the edge of the palm while observing the chin (there is a neural connection between the two). The reflex is present in all newborns. In adults, the normal response is no contraction. In states of dementia, frontal lobe disease, and assorted brain degenerations the mental reflex is positive, indicating a disruption of normal inhibition from the neocortex and a corresponding increase in emotional tone [3]. The muscle’s contraction in states where there is no brain damage signals a robust emotional stirring and that the individual is aroused.

Early on the press nicknamed the President “No Drama Obama” to indicate his apparent unflappability. But photos that you can google yourself show how his face betrays different inner thoughts. His mentalis is contracted, his eyes narrowed, and the corners of his mouth strongly turned down. Often he bites his lip, hard. It is for viewers to infer whether the President is feeling anger, frustration, disdain, or boiling rage. But he does not look happy. And definitely not cool.

Craig Baxter/

We have separate voluntary and emotional motor pathways.

One of the most common illustrations of our separate voluntary and involuntary motor pathways occurs in stroke. It is an early lesson we teach to medical students. A typical stroke leaves a patient paralyzed on one side because it affects the voluntary pyramidal motor pathways (the name comes from the pyramid shape of these nerve tracts). Affected individuals can’t move the lower half of their face on the paralyzed side when told, “Show me your teeth,” or “Smile.” Yet if something unexpected amuses them, they smile symmetrically with those same “paralyzed” facial muscles given that emotional actions travel by an independent extra–pyramidal route. Interestingly, the person has no sense of agency when the latter happens. In the first instance the patient says, “I can’t do that,” and in the second, “I didn’t make that happen.”

Emotions first evolved in our distant ancestors as supervisory routines for homeostasis, the propensity of all living creatures to maintain a stable internal environment. Homeostasis is like a thermostat (Greek status = “to make stand”), and all emotions relate to the management of life, survival, and well–being.

Biologically speaking, emotions are unlearned routines for solving problems or seizing opportunities. Harvard psychologist Stephen Pinker says, “Intentions come from emotions, and emotions have evolved displays on the face and body. Unless you are a master of the Stanislavsky method, you will have trouble faking them; in fact, they probably evolved because they were hard to fake” [4]. Children 1–3 years old readily decipher complex mind reading scenarios. So can many animals, as any dog owner will tell you.

The roots of emotional intelligence as a science trace back to Charles Darwin. In 1872, in The Expression of the Emotions in Man and Animals, he stressed that the display of emotion was important to survival and adaptation [5]. Today we regard emotionally intelligent people as being self–aware (they understand what their feelings mean), having self–control (they can manage those feelings), empathetic (they are sensitive to the intentions and attitudes of others), and possessing social skills by which they can address, temper, and even arouse emotions in others.

When, in the film Avatar, the planet’s inhabitants say, “I see you,” they refer to this deep perspicacity for reading others and intuiting their state of mind. The skill was outsourced eons ago to the unconscious where it became automatic. It isn’t that we don’t know that others constantly broadcast their attitudes and feelings, but that we give it so little thought.

Why do we have so many facial muscles when in terms of need we need only 2 to open and close the eyes, and 2 more to do the same with the mouth? If the remaining 50 are superfluous then evolution should have jettisoned them long ago given how much energy it costs to maintain them [6]. But evolution didn’t do away with them, indicating their important biological purpose.

There is a difference between a reasoned weighing of facts and an emotional weighing of matters. As Orson Welles says in Citizen Kane, “Nothing is ever better than finding out what makes people tick.” Social communication depends on reading others. We surmise what lies behind facial expressions, decipher body language, and interpret tone apart from literal words. We read between the lines. We hear what isn’t said. Seen from its component parts the task seems daunting, yet we do it effortlessly.

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[3] Links, K., et al., Prevalence of Primitive Reflexes and Parkinsonian Signs in Dementia. The Canadian Journal of Neurological Sciences, 2010. 37(5): p. 601-607;  Sanders, R.D. and P.M. Gillig, Reflexes in Psychiatry. Innovations in clinical neuroscience, 2011. 8(4): p. 24.

[4] Pinker, S., How the Mind Works. 2009, New York: Norton.

[5] Darwin, C. and P. Ekman, The Expression of the Emotions in Man and Animals. 4th ed. 2009, Oxford ; New York: Oxford University Pres