Neural Basis and Hemispheric Dominance of Facial Expressions of Emotion

Facial expressions of emotion are fundamentally automatic in nature.
They represent physiological responses that individuals cannot consciously control.
Actors frequently encounter difficulty when attempting to voluntarily produce convincing facial expressions of emotion on cue.
This difficulty led to the development of the concept of "method acting."
In method acting, rather than attempting to perform the physical act of smiling, an actor is encouraged to imagine a happy moment from their personal life.
The goal of this technique is to make the actor feel the genuine emotion, which then allows them to convey it more realistically to an audience.

A primary method for distinguishing between a genuine expression of emotion and a fake one involves identifying specific muscle contractions.
Genuinely happy smiles require the contraction of muscles located near the eyes.
The specific physical trait of eye muscle contraction is known as the Duchenne marker of emotion.
In historical research, Doctor Duchenne conducted experiments by electrically stimulating the facial muscles of volunteers. * By stimulating muscles around the mouth, Duchenne could produce the appearance of a smile. * However, these smiles were identified as appearing "fake" or non-genuine. * The lack of realism was attributed to the absence of the contraction of muscles around the eye, which is necessary for a genuine emotional expression of happiness.

The study of two specific neurological disorders provides evidence for the neural basis of genuine emotional expression. These disorders demonstrate that voluntary facial movement and involuntary emotional expression utilize different brain mechanisms, even though they involve the same underlying muscles.

Definition: A condition where patients are unable to voluntarily move their facial muscles upon command.
Contrasting Ability: Despite the inability to move muscles intentionally, the patient remains capable of expressing genuine emotion using those same muscles.
Case Study Observations: * Patient: A woman appearing in the top $2$ panels of the study figure. * Voluntary Attempt: When asked to pull her lips apart to show her teeth (Panel A), she is unable to move the left side of her face. * Underlying Cause: This deficit is caused by a lesion in the face region of her right primary motor cortex. * Spontaneous Expression: When the woman laughs or exhibits genuine emotional expression, both sides of her face move normally and symmetrically.

Definition: A condition where a patient can move facial muscles voluntarily but fails to express emotion on the affected side of the face during spontaneous reactions.
Case Study Observations: * Patient: A man appearing in the bottom $2$ panels of the study figure. * Voluntary Attempt: When the man attempts to pull his lips apart to show his teeth (Bottom-left section), he exhibits no difficulty and moves both sides of the face. * Spontaneous Expression: When the man laughs or smiles genuinely, only the left side of his face responds. * Underlying Cause: This condition resulted from a stroke that damaged the white matter of the left frontal lobe.

The brain’s hemispheres play distinct roles in managing emotions.
The right hemisphere is dominant in the recognition of emotions.
The right hemisphere is also the dominant hemisphere for expressing emotions.
Due to the principle of contralateral control, the right hemisphere’s dominance results in the left side of the face producing stronger expressions of emotion than the right side of the face.
Experimental Evidence from Photograph Studies: * Researchers conducted a study where photographs of individuals expressing various emotions were cut into left and right halves. * New composite faces were created by combining two left halves (one being a mirror image) or two right halves. * Findings: The composite faces created from the left halves of the original faces showed significantly stronger emotional expressions compared to those created from the right halves.