The famed stallion Black Beauty felt joy, excitement, and even heartbreak—or so he tells us in the 1877 novel that bears his name. Now, scientists say they’ve been able to detect feelings in living animals by getting them straight from the horse’s mouth—or in this case, its head. Researchers have devised a new, mobile headband that detects brain waves in horses, which could eventually be used with other species.
“This is a real breakthrough,” says Katherine Houpt, a veterinary behaviorist at Cornell University who was not involved with the work. The device, she says, “gets into the animals’ minds” with objectivity and less guesswork.
Ethologist Martine Hausberger had the idea while investigating whether stressed horses had a harder time learning to open a sliding door over a food box. (Spoiler alert: They do.) Hausberger, of the University of Rennes, noticed some of the animals—specifically, those living in cramped spaces—were paying less attention to the lessons. Were they depressed?
An electroencephalogram (EEG) could theoretically pick up on such a mental state. Scientists have used the devices, which record waves of electrical impulses in the brain, since the early 1900s to study epilepsy and sleep patterns. More recently, they’ve discovered that certain EEG waves can signal depression, anxiety, and even contentedness in humans. EEG studies in rodents, farm animals, and pets, meanwhile, have revealed how they react to being touched by a human or undergoing anesthesia. But so far, no one had found a way to record brain waves in animals while they move around.
That’s because EEG recordings require placing electrodes in specific positions on the head and running cables from them to a recording machine. As a result, animals are either restrained or sedated during measurements. And for readings to be accurate, scientists have to either shave the animal’s head or surgically implant the electrodes under its scalp.
Hausberger turned to her Rennes colleague, neurophysicist Hugo Cousillas. He started with wearable EEG headbands for people, which promise to show how well we’re sleeping or meditating by tracking brain waves.
Cousillas spent the next 6 years developing a device for horses. Unlike EEGs for people, which can have dozens or even hundreds of electrodes, the horse headband only has four—plenty for picking up waves from both hemispheres of their peach-size brains. The device transmits its readings up to 20 yards, and the animal’s hair remains intact—thanks to electrodes nestled in spring-loaded, gel-filled pockets with tiny needles poking gently against the skin.
Cousillas and Hausberger then teamed up with Rennes ethologist Mathilde Stomp to take EEG recordings of 18 horses. Half lived in individual stalls in a classic, confined stable, whereas the other half roamed with herds on open pastures.
The two groups had very different EEG profiles. Horses in stables showed an average of 2.5 times more right-hemisphere “gamma” waves than those in open fields. In people, such waves are often a sign of anxiety, distraction, or depression. The horses that spent most of their time out in the open, meanwhile, showed twice as many left-hemisphere “theta” waves on average—generally a sign of a calm and attentive mind, the team reports this month in Applied Animal Behaviour Science. “What’s really exciting about these results is that they give us a rare measure of ‘happiness,’ so to speak,” Hausberger says.
Konstanze Krueger, a cognitive ecologist at the University of Nürtingen-Geislingen, isn’t so sure. Brain wave interpretations for humans don’t necessarily translate to other species, she says.
Still, the new approach is a “fascinating” way to measure captive animals’ mental health, says Greg Vicino, an animal behaviorist at the San Diego Zoo. To monitor behavior and mood in hundreds of animals, his team watches each one for hours; the headband may be a promising alternative.
Getting a headband on a tiger might seem terrifying, Vicino says, but most of the animals at his zoo are trained for basic handling and could probably get used to wearing such a device. “It’s not a deal breaker.”
sciencemag.org, 9 March 2021