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We humans often say that a dog’s roar is “angry” or that a cat is “happy”.
But these terms are of little use to scientists like David Anderson, a professor of biology at Caltech, who studies the circuits of the brain involved in mental behavior. “We need to do more than just express our emotions to other animals, because animals are not small people in fur,” he said.
And animals can’t tell us how they feel. Yet Anderson believes that a connection exists between the emotions of animals and humans.
“Emotions are brain functions that have evolved over time through natural selection,” he says. “They didn’t just appear on the planet with the advent Homo sapiens“
This idea is central to Anderson’s latest book, Animal Nature: How Emotions Guide Us. It is the focus of growing scientific efforts to find new treatments for disorders such as PTSD by manipulating emotion-related brain circuits in animals.
In his book, Anderson describes research from his lab that suggests that there are many similarities between the underlying brain circuits of human emotions and those found in rats and even fruit flies.
Feelings vs. Emotions
To study emotions in animals, Anderson says scientists must first put away their own perceptions that people generally think of as emotions, such as anger, fear, sadness, or joy.
In other words, they have to look beyond the people Feelings.
“Part of the feeling is just the tip of the iceberg above the ocean of our consciousness,” Anderson said. “The bottom line is what we share with animals.”
What lies beneath the senses, he says, is the state of the brain that creates certain behaviors. And that’s part of the emotion that scientists can study. Anderson’s lab, for example, investigated fruit flies that became much more active when they saw a moving shadow cast by a flying hunter.
“We see that every time we provide shade, the flies become more leaping, until they are literally hovering like popcorn,” he said.
And even after the shadow is gone, the flies continue to run.
Anderson would behave the same way if he was on a trip and saw a rattlesnake.
“I would jump in the air,” he says. “But for a few minutes after the snake had gone into the bush, my heart would pound, my face would dry up, and I would jump whenever I saw a snake-like object in front of me – even if it was a stick.”
This type of behavior is characteristic of an endless brain condition called protective arousal. It exists in both fruit flies and humans, which is why Anderson believes that studying the fear of insects or rats can reveal a lot about human emotions.
“We can try to figure out how the brain is creating that condition and what makes it so long lasting and what finally calms the animal,” Anderson said.
In the case of rats, the answer seems to be specialized brain cells that become hyperactive when a rat detects a threat and gradually returns to normal after the threat has subsided. Anderson suspects that people have similar cell groups that create feelings we know as fear.
Aggression across species
Another human emotion that is probably rooted in animal emotion is anger.
There is no way to know if animals have angry feelings, says Dao Lin, a neuroscientist at New York University. But aggressive behavior associated with human anger is found in fish, reptiles, birds and mammals.
So Lynn is studying the regions of the brain involved in aggression. And he has found one that seems critical.
“It’s a tiny, tiny area deep in the brain and we all have it,” he says.
In humans, this region is below the hypothalamus, just above the pituitary gland. And studies show that in rats and other animals, this group of brain cells is part of a basic aggression circuit.
“We can provoke aggression by artificially activating this area in rats,” Lin said.
Turn it on and a mouse will attack. Stop it and even the natural aggression of an animal disappears. There is some evidence that it can also occur in humans. Doctors sometimes use deep brain stimulation to deactivate the aggression circuit in highly violent mental patients.
“Aggression is usually uncontrolled,” Lin said. “It’s usually the last resort.”
Trauma, fear and PTSD
Animal emotions are also helping scientists understand some mental disorders, including post-traumatic stress disorder (PTSD).
“We really see PTSD as a disorder in which this evolving, critical fear response has largely gone too far,” said Dr. Kerry Wrestler of Harvard Medical School and MacLean Hospital.
For a person with PTSD, even a small incident can create a stressful and frightening response that lasts for hours, Wrestler says. And there is a parallel between the animals.
A normal mouse will freeze when it hears a tone associated with a light electric shock. But when the shock stops, the animal soon learns to ignore the tone.
Trauma changes that learning curve.
“If the animal had been traumatized before, they would learn faster, they would be frozen for longer, and it would take them longer to extinguish or learn that the tune is actually safe,” Wrestler said.
In both humans and rats, trauma is seen to alter the brain circuitry involving the amygdala and the prefrontal cortex. And in rats, it is possible to control that circuit.
“We now understand certain parts of the circuit that increase fear and other parts of the circuit that reduce fear,” or at least the animal version of that emotion, Wrestler said.
The next step, he said, is to figure out how to change that circuit to reduce the fear response of people with PTSD.