A longstanding debate about whether animals have emotions and feelings is being reshaped by new tools and concepts.
Why it matters: Understanding whether non-human animals have emotions — and how they are formed if they do — could provide new insights into the mental health of humans.
The big picture: Emotion is tricky to study. There isn't a formal, widely held definition of what an emotion is, and neuroscientists, biologists, psychologists, anthropologists, sociologists and philosophers all have different views.
One question among them centers on how much emotions are hardwired in networks of neurons in the brain that may even be found across humans, mammals and other animals, or if they are the products of a conscious brain influenced by culture, experience and learning.
Many studies of human emotion have leaned on asking people across cultures to match facial expressions to emotions. That they often assigned the same emotion to the same expression led some psychologists to conclude there are a handful of universal basic emotions like fear or anger that are innate.
But the method is criticized by some researchers and the idea of basic emotions is contested. "Nobody can tell you what the rules are for getting non-basic emotions out of basic emotions," says Andrew Ortony, a professor emeritus of psychology at Northwestern University who leans to the side of culture guiding emotion.
Primatologist Frans de Waal of Emory University, who studies behavior in chimpanzees and other animals, also says to continue focusing on the face as the window to emotional experience is "misguided" but for different reasons. It omits animals without facial expressions, like dolphins or fish, and it implies love, hope and other emotions not in the basic bucket are uniquely human, he says.
"I think all emotions that humans have are variations on animal emotions," he says.
What's new: Increasing evidence suggests crabs and some other invertebrates — in addition to fish and mammals — experience emotions, de Waal and philosopher Kristin Andrews of York University in Toronto write in Science today.
Crabs have been found to stay away from parts of a tank where scientists have shocked them. De Waal and others argue such learned behavior isn't an unconscious reflex because the crabs are actively avoiding those spots, meaning they must be centrally processing that going there does not feel good.
But by Ortony's definition, that is not the same as experiencing emotions, he says.
Studying the biology of emotion in mice, fruit flies, jellyfish and other animals is also important because it allows scientists to perform biological experiments they can't do in humans, Caltech neuroscientist David Anderson writes in his new book, "The Nature of the Beast."
They can use tools like optogenetics to switch neurons on and off in the brains of rodents and other animals to see whether they cause an emotion or if their activity is a consequence of an emotion.
That information "matters if you are trying to decide which type of neuron to study in order to search for a new treatment for anxiety disorders," he writes.
The big problem: Unlike humans, other animals can't tell scientists if or how they feel. (Humans aren't exactly reliable here either: We lie about our feelings, aren't aware of them at times or just can't describe them. Ask any therapist.)
But Anderson argues that doesn't matter. For him and others, emotions are internal, unconscious states of the brain's neurons that exist separate from a feeling, which is conscious.
These emotional states can be seen in behaviors like aggression, which have different properties — they persist and their intensity can vary — that distinguish them from reflexes, Anderson writes.
Those "emotion primitives" are seen in the behavior of mice and fruit flies, and in the neurons in their brains that are associated with those behaviors, he writes. That suggests they are common and innate — but he says that doesn't mean flies' emotions are as complex as those of mice or humans.
But, but, but ... New York University neuroscientist Joseph LeDoux, whose research focuses on fear, argues these ancient circuits of neurons seen in different species may very well control defensive behavior but that fear is a conscious feeling assembled through cognition, which evolved more recently.
Most scientists acknowledge part of the confusion and cross-talk about emotion in science is rooted in the loose language of our everyday experience as humans that can affect how even they talk about emotions and feelings, with the terms used interchangeably.
And some suspect emotions and feelings arise from a combination of culture and biology.
What to watch: Lisa Feldman Barrett, a professor of psychology at Northeastern University who has championed the idea that emotion is culturally constructed, recently wrote that "genes and environment are so deeply entwined ... that it’s fundamentally unhelpful to call them separate names like 'nature' and 'nurture.'"
In a recent study, psychologists Gaurav Suri of San Francisco State University and James Gross from Stanford University built artificial neural networks representing facial expressions, physiological responses or other features of emotion to model how an emotion occurs.
When they gave the network inputs, they found in some circumstances the network responded in a way that is consistent with theories that say emotions are the same across people and innate, and in other circumstances with the idea that emotions are constructed or learned.
Suri cautions it is just a model but it suggests "emotions are emergent phenomena arising from many diverse interactions. It's no use fighting about whether emotions are basic or constructed."
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