Two high-profile, officer-involved shootings in the Twin Cities are tragic indicators of the growing role that fear and anxiety have on society.

In one, St. Anthony officer Jeronimo Yanez was “scared to death” during a 2016 traffic stop and shot seven times at the driver, Philando Castile, who he thought was pulling out a handgun. In the other, Minneapolis officer Mohamed Noor was reportedly startled by a noise in a dark alley July 15 and shot a woman who approached his vehicle.

These incidents reflect the constant tug of war in the fear circuitry of human brains, between the natural “fight or flight” response to frightening events and the logic center that tells people not to worry.

Some experts believe easy access in the information age to stories about police shootings or killer viruses or fish biting swimmers is breeding more fear, and that could have a compounding effect over time if these fears are passed down from parents to children.

“There’s reasonable fear and there’s unreasonable fear,” said Seth Norrholm, who studies fear at Emory University’s Human Psychophysiology of Emotion Laboratory in Atlanta. “It’s reasonable to be afraid if you’re walking in a dark alley and there’s a potential perpetrator. Unreasonable fear would be, ‘I’m concerned that my apartment is going to be hit by an IED or a terrorist bomb’ ” every day.

Fear is the brain’s defense system, triggered by combinations of physical movements — quickened pulse, narrowed eyes, tensed muscles — that suggest the potential for danger. The limbic system in the brain interprets these signals and tells the sympathetic nervous system to release hormones such as cortisol that heighten awareness and muscular energy to escape danger.

Meanwhile, the frontal cortex in the brain acts as a counterbalance — differentiating people from fish or lizards in their gut reactions to fear — using experience and logic to assess perceived danger.

“If those systems aren’t working in concert with one another, you could develop a lot of dysfunction,” said Dr. Katharine Nelson, a psychiatrist and neurologist at the University of Minnesota. “You could be walking down a path and see a stick out of the corner of your eye and your automatic thought process might tell you ‘there’s a snake there’ ... and you might run the other direction and never go down that walking path again.”

Experts such as Shmuel Lissek at the U’s ANGST Laboratory describe three basic responses to fear — protecting oneself from actual danger, ignoring the danger and getting hurt, and protecting oneself in the absence of danger.

Lissek said that people have evolved over time toward the latter, better-safe-than-sorry approach. That can be problematic if it’s based on stereotypes or false fears.

Incidents of discrimination were reported against African-born immigrants in the U.S. during the West African Ebola epidemic, and earlier against the first people infected with HIV, for example.

Whether people are more afraid today is a matter of dispute, but Norrholm said mass media exposure to traumatic events is increasing the opportunities for people to react unreasonably to fears.

“When the Zika virus was all the rage in the media, you’d view these headlines and they would say something along the lines of, ‘chance of Zika outbreak increased today,’ ” Norrholm said. “Now it increased, sure, but from about 0 to .0001. One of the things I’m trying to do is help people understand to keep fears reasonable.”

Norrholm recently wrote an article for to give people coping strategies when bombarded by frightening news.

Rising fear appears to be a concern in law enforcement. A Pew Research Center survey of nearly 8,000 U.S. police officers earlier this year found that 93 percent are more worried about safety today than they were earlier in their careers.

Yanez was acquitted in the shooting, after testifying that his wife and children flashed before his eyes as he believed Castile was drawing a weapon.

“I was scared to death,” he testified. “I thought I was going to die.”

Officials with the Minneapolis Police Department declined to discuss how fear is addressed in police training, given ongoing investigations into Noor’s shooting of Justine Damond, who had called police about a potential assault taking place behind her house. The first words in the department’s training officer handbook are that officers must have “the ability to manage fear and take the just and moral actions necessary to accomplish a mission or goal.”

Knowing how fear primes the body to react, Nelson said she has empathy for officers and others in hazardous jobs.

“People in those professions are going to have a lot of cortisol pumping through their body,” said Nelson.

Experience and repetitive training are needed to help them temper their fight or flight instincts, she said.

Behavioral studies have suggested that people are born with two fears — of falling and of loud noises. The rest, such as fears of snakes or spiders, are developed over time due to experiences.

Genetics play a role, though, and explain why people react differently to fear. Some crave thrills such as roller coasters or horror films, Nelson said, which produce the same chemical responses as actual fears and build up tolerance.

For others, the buildup of frightening events has the opposite effect.

“You may have people who are so fearful and have such a profound stress response that they literally don’t leave the house,” Nelson said. “Then they don’t leave their room, and then, over time, it’s a closet because they have this exaggerated fear.”

For mild fears, simple steps such as breathing out more than breathing in can slow the pulse and reduce the body’s automatic fear response.

For people with severe fear-based disorders, such as soldiers who relive wartime trauma when they hear loud noises, treatment generally involves exposure therapy to help them tolerate their fears. Research at the U includes methods to make exposure therapy work faster.

One concern about rising fear levels in modern society is that parents might be able to genetically pass along fears they develop in their lives. Norrholm has seen that in studies of rats.

Norrholm said he also wants to discourage people from reactions based on stereotypes or incomplete information. He said he worries that people might assume based on the two recent shootings that police officers are more dangerous. And he worries that officers might have unreasonable fears triggered by racial or other stereotypes of suspects.

“Is your fear proportionate to the information that you have?” he asked. “Oftentimes it’s not.”