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In the the story of Walt Disney's “Pinocchio,” the boy puppet's lies are revealed whenever his wooden nose grows. Since then, a “growing nose” has been synonymous with being caught in a fib. It turns out that this idea isn’t too far from the truth.

Researchers at the University of Granada in Spain found that when people lie, their noses and orbital muscles become hot, a condition they call the Pinnochio effect.

Emilio Gómez Milán and Elvira Salazar López have been using thermographic cameras to record people as they discuss subjective experiences, when they perform different dances, and when they become sexually aroused (no surprise that sexual excitement causes additional heat to emanate form the genitals and chest, a little less so for women than men). Thermography detects body temperature; it's the technology that allows night vision to work.

“Our main objective was to look for somatic markers of quale -- feelings, emotions, and subjective experience that cannot be easily verbally explained but only experienced, like love or religious experience or beauty. Is it possible to differentiate [between] a person who every Sunday [says] the Lord’s prayer but in fact is a nonbeliever?” Gómez, an assistant professor of psychology, writes via email.

The researchers asked subjects about subjective experiences—such as whether a piece of art was beautiful or whether they believe in God—while in an fMRI or in front of the tomographic cameras. This allowed Gómez to see what occurred in the brain and what happened to facial temperature when a person described quale. He then compared the data from two imaging machines to see if there was any overlap in brain activity and facial temperature. Other researchers have found that fMRI effectively shows when someone is being less than truthful, such as when a person admits to liking a painting but really does not believe it.

When people fibbed, the temperature in the muscles around the nose and the eyes, heated up while other areas of the face cooled. This corresponds with action in the insular cortex, nestled deep within the cerebral cortex, which controls emotions, our subjective sense of our inner blood, blood pressure during exercise, and perception of pain. Stronger negative or conflicted feelings increase activity in the insular cortex, leading to more heat emanating from the nose and orbital muscles.

Gómez believes that temperature in these regions increase because the activity in the insular cortex prompts a physiological change.

“These two changes (insula activation and temperature changes) are the two sides of the same coin,” he says. Because the insula aids in the regulation of body temperature, it comes as little surprise that body temperature increases during emotional experiences.

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