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FAMILIAR FEELINGS: How do we know what emotions animals feel?

As researchers settle on ways to parse different emotional states, and on a more basic level, perhaps even ways to identify sentience, we might find a wider basis for a shared inner life across the animal kingdom.

ALLA KATSNELSON: Scientists studying animal behavior and animal welfare are making important strides in understanding how the creatures we share our planet with experience the world. “In the last decade or two, people have gotten bolder and more creative in terms of asking what animals’ emotional states are,” explains Georgia Mason, a behavioral biologist and animal welfare scientist at the University of Guelph in Canada. They’re finding thought-provoking answers amid a wide array of animals.

For instance, recent studies hint that picking up a mouse by its tail casts a pall on the animal’s day, and that an unexpected sugar treat may improve a bee’s mood. Crayfish might experience anxiety; ferrets can get bored; and octopuses, and perhaps fish, can experience pain.

Such findings could drive changes in how we treat the animals in our care. For instance, a broad scientific review published in November 2021 by the London School of Economics and Political Science concluded that certain invertebrates such as crabs, lobsters and octopuses should be considered sentient — that is, capable of subjective experiences such as pain and suffering. The conclusions suggest that protection afforded by animal welfare laws should extend to these creatures. One possible outcome: Updates to U.K. animal welfare legislation may make it illegal to boil lobsters alive, requiring swifter, less painful methods to kill the animals.

To determine how content a horse is with its life, people who care for horses would typically look at things like ear position, posture and how attentive the horse is to its environment. Blood markers for anemia, indicating chronic stress, and signs of overall wellness such as appetite and immune system health could also shed light. Recently, Martine Hausberger, an animal scientist at CNRS at the University of Rennes in France, and her colleagues tested a more specific and direct measure: the brain waves of horses, collected using electroencephalography, or EEG.

In people, EEG can help assess sleep patterns or diagnose conditions such as epilepsy, stroke or head injury, and researchers now think certain types of brain waves can indicate depression. EEG has been used in animals in veterinary clinics and in laboratory studies, but Hausberger wanted to bring the tool to the animals’ home turf. Her team created a simplified, portable EEG device that provides “a sort of summary of brain activity,” she says. Five electrodes are placed on a horse’s forehead, attached to a lightweight headset.

The researchers used this headset EEG to gauge the welfare of 18 horses that wore the device for six 10-minute observations. The results, published March 2021 in Applied Animal Behaviour Science, give a snapshot into the secret lives of horses. The horses that roamed with their herd outdoors, grazing at will, had more brain waves called theta waves, which have high amplitude and move slowly. In humans, theta waves are thought to reflect calm and well-being. By contrast, the animals that lived in solo stalls with little contact with other horses had more gamma brain waves, the fastest of all brain waves. In people, gamma waves are associated with anxiety and stress…

For most of the last two millennia, Western thinkers roundly rejected the notion that animals have the capacity for feelings. Charles Darwin bucked that trend, proposing a shared evolutionary capacity for emotion across species in his 1872 book, The Expression of the Emotions in Man and Animals. Take fear, for example: “With all or almost all animals, even with birds, Terror causes the body to tremble,” he wrote. But a psychological theory called behaviorism, which gained prominence in the early 20th century, put a decades-long pall on research into animals’ inner lives… That started to change near the end of the 20th century…

One approach involves investigating animals’ feelings through the lens of human psychology. Looking for parallels in how humans and other animals process experiences makes sense because our brains and behaviors reflect a shared evolutionary history, says Michael Mendl, an animal welfare researcher at the University of Bristol in England. Researchers routinely probe the minds and brains of rodents and other animals, including flies, fish and primates, to study and develop drugs for human mental disorders such as depression and anxiety. So we should be able to work backward from humans to study feelings in other animals too, Mendl says…

Pain, too, is experienced by many animals. Pain has two components, says behavioral and welfare scientist Matthew Leach of Newcastle University in England. One component is physical, simply consisting of the activation of sensory receptors, nerve cells firing or other physiological features — pain’s plumbing, you could say. Animals respond to it with a reflex reaction or a basic learned response; no conscious awareness is required.

The other component is emotional, which is trickier to measure because it manifests in more complex behaviors. For example, mice, which like an ambient temperature up to 10 degrees Celsius higher than in most research labs, build intricate nests in their cages that help them regulate body temperature. When the animals are in pain or distress, their nest-building abilities fall apart.

Facial expressions are a more direct way to assess pain or other types of distress in animals, Leach says. His lab team and others have identified a range of expressions in more than a dozen species, from mice to horses. With less than 30 minutes of training, people can learn to accurately see grimaces in animals’ faces, Leach says. Those faces can reveal more than pain. Using artificial intelligence algorithms to scan videos of mouse faces, researchers have identified a whole range of emotions — pleasure, disgust, fear — encoded in the tilt of the ears or a curl of the nose…

Researchers are still figuring out where to draw the line across the animal kingdom. That question prompted the recent U.K. scientific assessment of sentience. The researchers involved reviewed all the literature they could find that might point to clues about the inner lives of cephalopods and crustaceans — studies on behavior and physiology, neuroanatomy and common practices in the seafood industry. The group’s eight-point checklist considered factors such as whether an animal’s nervous system could integrate different types of sensory information, and the complexity of the animal’s pain-sensing machinery.

“There’s a lot of information out there about animal behavior that is actually relevant to questions of sentience in a way that hasn’t always been appreciated,” says report author Jonathan Birch, a philosopher of science at the London School of Economics and Political Science. But for these species, “there’s not been a lot of intentional investigation”… As researchers settle on ways to parse different emotional states — and on a more basic level, perhaps even ways to identify sentience — we might find a wider basis for a shared inner life across the animal kingdom. SOURCE…


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