AU12 — Lip Corner Puller
The Action Unit produced by the zygomaticus major muscle, which pulls the corners of the mouth obliquely upward — the basic mechanical smile.
AU12 describes an upward pull at the lip corners and appears in many smile configurations. Neither AU12 alone nor its combination with AU6 verifies why a person smiled or how they felt.
Tracking AU12 intensity and co-activation over time provides a structured record of visible movement for contextual review.
Related terms: action unit, duchenne smile, au6 cheek raiser, facial action coding system
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