The following post is about AU1 – inner brow raiser, driven by the medial part of the frontalis muscle. It covers: anatomical variation, common mistakes, and provides clean references. 

 

What is Inner Brow Raiser?

Inner brow raiser, or AU1, is a Facial Action Coding System (FACS) action unit (AU). Its function is to raise the medial brow/forehead area, and its action is triggered by the contraction of the medial region of frontalis. It can difficult find clean references inner brow raiser. When building FACS references, many sources fail to:

1. Find actors who can voluntarily trigger their medial frontalis without also contracting the lateral area of frontalis or corrugator supercilii. 
2. Properly direct models to perform medial frontalis contraction.

In our everyday lives, most of us can effortlessly raise our inner brows without thinking twice; however, when commanded to, many people struggle to isolate this motion.

FACS References & Misinformation

I recently (2020) critiqued a set of FACS shapes for a client and noticed his inner brow raiser shape had some corrugator (from brow lowerer) mistakenly mixed in.

Client’s Inner Brow Blendshape + My Notes:

Adding corrugator to inner brow raiser is a very common mistake. This commonality is partly due to the fact that: Good references are hard to find!

Even my client – an established industry artist with a great portfolio and CV – unknowingly added corrugator features to his model, because he trusted a tainted reference. The reference he used was from a prominent anatomy and facial expression book: Anatomy of Facial Expressions. Many art students and professionals use this textbook. It is a great textbook, but some of its FACS shapes are inaccurate.

Reference used by client:

See the vertical and wavy lines in the center of the forehead in the images below? Those vertical lines are from a brow knitting muscle known corrugator supercilii.

To view some clean examples of medial brow raising, observe the GIFs below. Read about the primary and secondary effects of inner brow raiser as well as how its features can vary across individuals.

Clean AU1  – Inner Brow Raiser Examples

example i

example ii 

For more information see: The Secret Life of Inner Brow Raiser.

For a full and structured FACS deep dive, see my online course, the: FACS Cram Session.