Have you ever felt your ear muscle move when you strain it to listen to something? 

The auriculomotor system (the ability of human ear muscles to orient towards sounds) traces persist in the brain that have been discovered by scientists at Saarland University in Germany, a hidden reflex deep in the human brain, which they believe connected back to our evolutionary past.

The neural circuits that are responsible for this movement haven’t fully disappeared, although our ears no longer swivel like a dog’s or a cat’s.

“Most humans cannot move their ears voluntarily and the associated muscles activate in response to the auditory effort and this point was discovered by Lead author Andreas Schröeer and his team." by Andreas Schröeer.

The Science Behind the Phantom Reflex

Schroeer the first author of the study in Frontiers in Neuroscience explained that three large muscles connect the auricle to the skull and scalp and are important for ear wiggling.

Researchers caught up 20 volunteers to electrodes that documented the activity of their auricular muscles. Participants listened to an audiobook while distracting podcasts played in the backdrop at different volumes.

The hardship of differentiating the audiobook from the background noise ranged across three scenarios:

1. Easy: The audiobook was much louder than the podcast, with clear differences in the pitch.

2. Medium: The podcast volume is increased making the distinction much harder.

3. Difficult: Two podcasts played simultaneously at a more increased volume, with one matching the audiobook’s pitch.

The study found that ear muscles are activated more when the listening task has become much harder. Generally, the superior auricular muscle lifts the ear and the posterior auricular muscle pulls the ear backward.

In the research study, it's very interesting to notice that the muscles have responded differently based on the sound direction and the posterior and superior auricular muscles reacted during attentive listening.

When audio came from the back, the posterior auricular muscles displayed more activation, imitating how animals would move their ears toward an unseen sound source.

Even more interesting is that none of the participants could voluntarily move their ears, suggesting that these muscle activations occurred subconsciously.

Schroeer says the exact reason the ear muscles became vestigial is difficult to answer as our ancestors lost the ability over 25 million years ago. 

What's the reason behind understanding this?

The scientists believed that the research could help to understand the listening effort and hearing strain and also practical applications. Most of the evolution process has lots of examples that could explain vestigial reflexes( Palmar grasp reflex in infants, wisdom teeth, appendix).

So, the discovery remains significant for the following reasons:

• Newer ways for measuring listening fatigue-  Assessing the ear muscle activity can help to process the objective of how much effort is required to process sound that could help in people with hearing inabilities.

• Explains the connectivity of the brain to the ear where the research has put forward that the brain sends signals to control the muscle activity reflexes.

• More suitable hearing aids – If a hearing aid can catch ear muscle activity, it could help in adjusting settings in real-time to reduce listening effort.

Though our ears have forgotten the movement, our brain still sends signals that explain the evolutionary journey.

References:

1. Electromyographic correlates of effortful listening in the vestigial auriculomotor system” by Andreas Schroeer, Farah I. Corona-Strauss, Ronny Hannemann, Steven A. Hackley and Daniel J. Strauss, 13 November 2024, Frontiers Neuroscience. https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2024.1462507/full

(Input from various sources)

(Rehash/Dr. Lakshmisahithi Tanneru/MSM)