On Saturday, July 4 a group of people traveling on a Red Line Metro train headed to Fourth of July festivities in Washington, D.C. watched as one young man brutally murdered another, but no one intervened. Widespread criticism of the “apathetic” response of onlookers, who reportedly did nothing to help the victim, erupted in the press and on social media. From the perspective of brain science, however, this scorn is misguided.

The attack occurred when a man boarded the train and snatched a cell phone from 24-year-old Kevin Joseph Sutherland. During the struggle the robber viciously beat, kicked and stabbed the life out of the young man, inflicting 30 to 40 knife wounds. Passengers fled to opposite ends of the car and watched Sutherland die. At the next stop the blood-spattered murderer walked casually off the train and escaped into the crowd. Police later arrested 18-year-old Jasper Spires in connection with the crime based on evidence recovered from the scene.

Washington Post columnist Petula Dvorak contrasted the inertia of the Metro riders with the heroic actions of passengers on United Flight 93 who resisted the September 11 hijackers, and with a local man, Dylan Rawls, who risked his life to save a stranger being violently attacked in a Bethesda, Md. parking lot last May. Some have cited the Metro tragedy as a sign of society’s moral decay, while others have boasted about how they would have dispatched the killer. Traumatized witnesses are undoubtedly agonized, second-guessing their reaction to the horror.

A a small, black folding knife similar to the one described in news accounts as being used in the July 4 murder of Kevin Sutherland. (Photo: R. Douglas Fields)

The finger-pointing reflects a fundamental misunderstanding of the neuroscience of how the brain responds to sudden threats. I know, because like Sutherland, I was once robbed on a subway, and I reacted the same way he did. I instinctively fought with the robber to get my wallet back. I succeeded, but I was lucky. Had my chance encounter been with a homicidal maniac like the one that accosted Sutherland, I could have been killed just as brutally. But I didn’t think. I just reacted. In a fraction of a second I risked my life in a fight with a criminal without any conscious deliberation. As a neuroscientist, I was driven afterward to understand the threat detection circuits in my brain, which guided my response.

The actions these threat detection circuits trigger—to fight, freeze or flee—have momentous consequences. Enormous amounts of data must be evaluated instantaneously. If done consciously this analysis would take too long. Moreover, the demands of this complex analysis would overload the feeble capacity of our conscious mind. “I wasn’t thinking,” Rawls told the Post while recalling his heroic act in the Bethesda parking lot. “Had I stopped, thought about it, weighted the pros or cons, had I had time to react, I might’ve scared myself out of helping.”

It may be comforting to indulge in speculation about how you would have responded to the deadly attack on Sutherland, but the fact is that it is difficult to know how anyone will react to a sudden threat. A person’s response depends on a complex set of situational factors, the nature of the threat, and the internal states of the body and mind at that moment—all assessed in a fraction of a second and acted upon instantly. The multiple factors and uncertainties mean that there is rarely one correct response to a sudden threat. The identical reactions Sutherland and I had to being robbed, with opposite outcomes, are a dramatic illustration of this paradox.

Some of the factors determining how one will respond to sudden danger are being identified as neuroscience begins to tease apart the complex circuitry of our brain’s threat detection mechanism. This circuitry is largely subcortical—that is, it operates beneath the level of consciousness. Of paramount importance in threat detection and rapid response is the amygdala, located deep in the brain, which alerts us to danger, learns from bad experiences, and engages the body’s automated “fight or flight” response. The amygdala  triggers this response when it activates the same region of the brain that controls other powerful unconscious urges including lust, thirst and hunger: the hypothalamus. The release of adrenalin and other neurotransmitters makes our heart race, muscles twitch, and body sweat as we move to battle or to flee.

Sudden dangers "hijack" the amygdala via a high-speed pathway from the retinas in our eyes to the center of the brain's threat detection network. (Illustration: ManosHacker via Wikimedia Commons)

Danger signals shoot through high-speed pathways to the brain’s threat detection circuits rather than engaging our cerebral cortex. For example, there is a high-speed pathway from the retinas in our eyes to the center of the brain’s threat detection region. Most visual information is transmitted to the cerebral cortex at the back of the brain where complex analysis enables us to interpret the shifting patterns of light in order to evaluate the colors, dimensions, motions and identities of different objects. But this sophisticated visual processing takes time—too much time to dodge a left hook, for instance. In bypassing the visual cortex, the rapid subcortical pathway from the eyes to the amygdala alerts our threat detection system like a motion detector in a home security system. No image is formed, but whatever has just intruded into our visual field should not be there! Thus the decision to engage or escape tends to be instinctual rather than deliberate.

Bystander apathy is a psychological phenomenon in which witnesses to a person being harmed are less likely to intervene the more people there are present. This is thought to be a consequence of the herding instinct of human beings to do as they see others do. But when many people are present it is a much more complex situation. This leads to confusion. Is the person being attacked a victim or another criminal involved in, say, a gang fight? The Metro riders who saw the assault on Sutherland experienced neither apathy nor confusion, however. They experienced terror.

I cannot know what those witnesses lived through on that train, but I am confident from my knowledge of neuroscience that they did exactly the right thing. Their response was not a matter of bravery or cowardice or apathy—it was a matter of mortal strategy. Engaging the homicidal robber physically could have resulted in mass casualties. From all the situational information those people rapidly assimilated, that was their collective conclusion. So the passengers tried to appease the robber with cash instead and no one else lost their life.

Honed by eons of evolution in a dangerous world of survival of the fittest, the reaction these neural circuits trigger is usually correct; otherwise our species would have gone the way of dinosaurs. This is why rational Monday morning quarterbacking about the passengers’ response on the Metro is misguided. No fault should be leveled against any individuals on that train. They did as their brain and evolution equipped them to do.