‘Obsolete’ muscle that wiggles ears actually activates while listening

A “useless” muscle that allows some people to wiggle their ears actually activates when we strain to hear something.

Our ape ancestors lost the ability to pivot their ears when they diverged from monkeys millions of years ago, but some of the muscles and brain neurons that underpin this trait remain in humans today.

Many scientists have assumed that these so-called auricular muscles are obsolete, even if they do enable ear wiggling. But in 2020, Daniel Strauss at Saarland University in Germany and his colleagues found that they actually become activated in response to hearing sounds from different directions, prompting them to wonder whether this also happens when people are concentrating on listening.

To explore this, the researchers got 20 people with typical hearing, all aged between 22 and 37, to take three hearing tests of varying difficulty. They all involved focusing on a 5-minute audiobook clip narrated by a female voice while skin sensors measured electrical activity in their auricular muscles.

In an easy test, the researchers quietly played a podcast hosted by a male voice at the same time as the audiobook. In a medium-difficulty task, they added a quiet clip of a female voice, similar to the one in the audiobook, to the set-up. In the hardest test, both background clips were made louder.

The researchers found that the largest auricular muscle, the superior auricular muscle, became most activated during the difficult test. “It’s pretty amazing to see this nearly forgotten muscle working so hard during effortful listening,” says Strauss.

The team didn’t assess if activation of this muscle assisted the participants’ ability to focus on the main audiobook, but measuring its activity could provide an objective way to assess listening effort. This could help develop better hearing aids, which aim to minimise listening strain, says Strauss.

But first, larger studies involving people of different ages and with a range of hearing abilities need to verify the results, says Yusuf Cakmak at the University of Otago in New Zealand. The team also didn’t account for eye movements or facial expressions, which can affect the activity of auricular muscles, he says.

Strauss hopes to address some of these points in the future. “More studies are needed to gain a deeper understanding of this ‘neural fossil’ in our brain and how to make use of it,” he says.