upper face expanded

AU1 – inner brow raiser 

frontalis, pars medialis

AU1 muscle - frontalis, pars medialis

FRONTALIS ANATOMICAL DIVERSITY: A major factor often out of many anatomical references is the variability of frontalis shape, size, and structure. Despite its diversity, the frontalis muscle is often presented homogeneously. It is presented as a muscle spanning across most of the forehead with a split (bifurcation) in the upper portion of the muscle (as shown in the image above). However, in reality, this bifurcation is not always present. Some portion of people have an uninterrupted frontalis (no split). Others have a frontalis fully split (does not meet together in the medial area) into two sections. Even within the cases where there is a bifurcation, the split varies in terms of where it occurs along the frontalis as well as how deep it goes. All of these factors – and more – affect the way in which the brows move as well as how a particular individual’s wrinkles form. Read more here.

AU1 - inner brow raiser GIFAU1 - inner brow raiser GIF

  • Difficult to perform voluntarily
  • Commonly combines with AU 2 to create full brow raise (AUs 1+2)
    • Full brow raise is a signature marker in speech for word emphasis, attentiveness, and punctuation
    • It is also a major component of the surprise emotion prototype, which features AU 5 and 25+26  (lips parted with jaw drop, respectively)
  • Combines with AU 4 to create prototypic brow configuration for sadness  (AUs 1+4)
  • Also combines with AUs 2 and 4 for fear emotion brow prototypes (AUs 1+2+4)

for a deeper dive on AU1:

  • The Secret Life of Inner Brow Raiser
    • This post and video will walk you through the variations in inner brow raiser and how to identify each person’s unique inner brow raising style – including your own! 
    • (If you are not a subscriber, the free version of this video is on YouTube) 
  • Inner Brow Raiser Deep Dive
    • This  post covers fundamental features of inner brow raiser.
    • It also goes over common misconceptions regarding inner brow raiser and how to recognize incorrect inner brow raiser references. (Spoiler alert: There are a lot of them.)
  • Compare AU1 to a full brow raise (1+2). Observe image below.

    AU1 - inner brow raiser vs. full brow raise static image

AU2 – outer brow raiser 

frontalis, pars lateralis

AU2 - outer brow raiser static image

AU2 muscle - frontalis, pars lateralis

FRONTALIS ANATOMICAL DIVERSITY: A major factor often out of many anatomical references is the variability of frontalis shape, size, and structure. Despite its diversity, the frontalis muscle is often presented homogeneously. It is presented as a muscle spanning across most of the forehead with a split (bifurcation) in the upper portion of the muscle (as shown in the image above). However, in reality, this bifurcation is not always present. Some portion of people have an uninterrupted frontalis (no split). Others have a frontalis fully split (does not meet together in the medial area) into two sections. Even within the cases where there is a bifurcation, the split varies in terms of where it occurs along the frontalis as well as how deep it goes. All of these factors – and more – affect the way in which the brows move as well as how a particular individual’s wrinkles form. Read more here.

AU2 - outer brow raiser - frontalis, pars lateralis GIF

AU2 - outer brow raiser GIF

  • Much easier to perform voluntarily than AU 1
  • Many people can only perform AU 2 on one side of face
  • Combines with AUs 1 and 4  for fear emotion brow prototypes (AUs 1+2+4)

for a deeper dive on AU2:

  • In the context of AU1 vs. AU2:  The Secret Life of Inner Brow Raiser (If you are not a subscriber, the free version of this video is on YouTube)
    • While this post and video is primarily focused on AU1 (inner brow raiser), there is valuable information on AU2 here as well.
  • Compare AU2 to a full brow raise (1+2). Observe image below.
    AU2 vs. AU1+2 image

AU4 – brow lowerer 

corrugator supercilii, depressor glabellae, depressor supercilii

AU4 - brow lowerer - before and after

AU4 muscle - corrugator supercilii, depressor glabellae, depressor supercilii

AU4 - brow lowerer - GIF

AU4 - brow lowerer - GIF

  • One of the easiest brow movements to make
  • Can be confused with AU 9 (nose wrinkler) – especially when combined AU 10 (upper lip raiser)
  • Combines with AU 1 to create prototypic brow configuration for sadness (AUs 1+4)
  • Also combines with AUs 1 and 2  for fear emotion brow prototypes (AUs 1+2+4)

for a deeper dive on AU4:

    • The 3 muscles that make up AU4 can move independently.

1. corrugator

        • tends to push the brows toward each other
        • can be referred to as “knitting” the brows
        • causes vertical wrinkles above the nose

2. depressor glabellae

        • technically considered a nasal muscle
        • tends to push the down the medial portion of the brows, above the nose
        • causes horizontal wrinkle above nasal root

3. depressor supercilii

        • technically considered an eye muscle
        • debated whether this muscle is its own distinct muscle or part of orbicularis oculi

          ***Many surgeons, dermatologists, ophthalmologists, and plastic surgeons argue strongly that depressor supercilii is a distinct muscle with its own movement. I’m with them on this one. I believe I have identified depressor supercilii action occurring in isolation (or near isolation); however, I was not able to find any depressor supercilii references to compare to. I am happy to hear feedback from anatomists and surgeons. See GIF below.

        • depressor supercilii
        • depressor supercilii
      •  

AU5 – upper lid raiser 

levator palpebrae superioris

AU5 - upper lid raiser GIF

AU5 - upper lid raiser muscle - levator palpebre superioris

AU 5 - GIF

AU5 - upper lid raiser - sideview GIF

  • Generally not easily confused with other AUs – but can be mistakenly perceived as present when a strong 1+2 combo occurs
  • More difficult to detect when combined with AUs 4 (brow lowerer), 6 (cheek raiser), 7 (lid tightener), or 9 (nose wrinkler)
  • Combines with AU 1 and 2 to create prototypic upper face configuration for surprise (AUs 1+2+5)

AU 6 – cheek raiser

orbicularis oculi, pars orbitalisAU6 - cheek raiser - orbicularis oculi, pars orbitalis

AU6 - cheek raiser - sideview -GIF

  • Another difficult voluntary AU to perform
  • When attempting to perform voluntarily, it is often accidentally paired with:
    •  AU7 (lid tightener) – because it is difficult to separate them intentionally (Compare anatomy images of 6 and 7 to see how close the muscle bands are to each other)
    • AU12 (lip corner puller) – because people often associate 6 and 12 together since they co-occur in happiness expressions (mentioned in bullet below)
  • Paired with AU12 (lip corner puller) in authentic (or well-posed) happiness displays
  • Also can appear in:
    • various sadness prototypes
    • expressions of pain
    • squinting
    • skepticism

for a deeper dive on AU6:

AU 7 – lid tightener

orbicularis oculi, pars palpebralis

AU7 muscle - oribulcaris oculi, pars palpebralis AU7 - lid tightener GIF

AU7 - lid tightener - sideview - GIF

  • Not as difficult to perform as AU 6  but co-activation of AU 6 increases in likelihood as intensity of 7 increases
  • Difficult to detect when combined with AU 9 (nose wrinkler)
  • Often appears during concentration, skepticism, or trouble seeing
  • Combines with AUs 4 and 5 in upper face anger displays

for a deeper dive on AU7: