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updated 4/17/2012 12:24:25 PM ET 2012-04-17T16:24:25

As prosecutors and defense attorneys prepare for the trial of George Zimmerman, the Florida man accused of killing an unarmed black teenager, experts say that while shooting a gun is quick and easy, the decision to shoot to kill is complicated and controlled by a primitive part of our brain that doesn't always act rationally.

Others add that shooting to injure and not kill can be difficult.

Zimmerman was charged with second-degree murder in the death of Trayvon Martin in a case that has put the national spotlight on race relations, gun laws and police conduct.

Martin's family and supporters rallied and pushed for an arrest of Zimmerman after a month and a half went by before he was arrested or charged in the shooting.

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Some observers say Zimmerman's defense may hinge on whether he shot in self defense after Martin attacked him, an account that he told local police. Martin's family argues that Zimmerman was the aggressor.

One expert says that higher level behavior, activities such as decision-making, memory and observational skills, which are controlled by the cerebral cortex, are usurped by a fast-acting part of the brain called the amygdala during a violent confrontation.

"It causes a shift in hormones, blood pressure, heart rate, it can even slow down digestion," said Catherine Pittman, professor of psychology at St. Mary's College in Notre Dame, Ind. "It's really a lower level of your brain that takes charge."

Pittman said the amygdala and cortex work simultaneously -- one processing higher level functions and one preparing the body to escape or do battle.

"There are many levels of the brain that are operating [during a confrontation]," she said. "Some are operating under your control and some operate so quickly that you can't control."


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The combination of fear and a weapon can lead to deadly consequences.

"If you feel in danger you don't think rationally or logically," Pittman said. "The problem is that a gun is an easy thing to operate. It just takes one movement of your finger. You can feel threatened and take an evasive action, or you could kill someone based on a perception that is not accurate."

In the past few months, there have been fatal shooting incidents in Texas, Oklahoma, California and Michigan. In all of these, residents shot and killed intruders who entered their homes.

In the Florida case, police say Zimmerman -- the captain of a Neighborhood Watch group -- pursued Martin in his vehicle because he said that he thought Martin was acting "suspicious" and "up to no good." Martin was walking to his stepfather's home in Sanford, Fla., from a grocery store when he was killed.

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People experience "tunnel vision" during the fight or flight response, according to Bethany Teachman, assistant professor of clinical psychology at the University of Virginia.

"They are less sensitive to contextual factors of their situation," Teachman said. "A narrowing and focusing of attention can have negative costs."

Shooting to injure someone is practically impossible, added Thomas Aveni, executive director of the Police Policy Studies Council, a non-profit research group in New Hampshire.

"Police are trained to shoot at the center of mass of the body that is exposed," said Aveni. "If a suspect is shooting around a corner of building, then you are shooting at the center of mass of his head. During a close engagement, then you are shooting at the center of mass of the body. Which in many cases in going to be fatal."

Aveni said that studies reveal that 80 percent of the shots fired by police officers actually miss their intended targets. Trying to aim for a leg or arm in stopping a violent suspect is just too difficult, he said.

Each police agency has their own rules governing use of deadly force, rules that were codified in a Supreme Court ruling in 1985 that stated that an officer's use of deadly force has to be restricted to when the officer has reasonable believe of imminent danger of death, according to Aveni.

All police officers must undergo weapons training each year. Most states allow citizens to obtain a weapon by applying for a permit, waiting a certain period of time, and registering fingerprints with a police database.

Some states also require people who want gun permits to have a clean police record, and take safety classes that are often available online.

© 2012 Discovery Channel

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