On Saturday, July 4, 2015, a horrifying bloodbath erupted before the eyes of passengers on the Red Line Metro subway train heading to Fourth of July festivities in Washington, DC. Wide-spread criticism in the press and social media erupted over the “apathetic” response of onlookers who reportedly said or did nothing to help the victim. But from the perspective of brain science, this scornful criticism is misguided.

A man on the Metro train snatched a cell phone from 24-year-old Kevin Joseph Sutherland. In the struggle the robber viciously beat, kicked, and stabbed the life out of the young man, inflicting 30-40 knife wounds. Passengers fled to opposite ends of the car and watched as the recent college graduate was murdered gruesomely. At the next stop the blood-spattered murderer walked casually off the train and escaped into the crowd. Police later identified 18-year-old Jasper Spires from bloody clothing, a knife, and other evidence found in a trash can.

In a commentary in the Washington Post, columnist Petula Dvorak contrasts the apathy of Metro riders with the heroic action of passengers on United Flight 93 who resisted the September 11, 2001 hijackers, and with a local man, Dylan Rawls, 31, who instantly risked his life to save a stranger being violently attacked in a parking lot. Disgusted, some cite the Metro subway tragedy as a sign of society’s moral decay. Others boast with empty bravado in online superhero fantasies about how they would have dispatched the killer. Traumatized witnesses are agonized, second guessing their reaction to the horror.

The finger-pointing reflects a fundamental misunderstanding of the neuroscience of how the brain responds to sudden threats. I know, because like Kevin 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 of the likes that intersected Kevin’s path, 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 deadly fight with a criminal without any conscious deliberation. As a neuroscientist, I was driven to understand the threat detection circuits inside my brain.

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 said in recalling his heroic act. “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 Kevin, 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 treat, and internal states of body and mind at the moment–all assessed in a fraction of a second and acted upon instantly. This must be so. The multiple factors and uncertainties presented means that there is rarely one correct response to a sudden threat. The identical reaction Kevin and I had to being robbed, with opposite outcomes, demonstrate this dramatically.

Some of the factors determining how one will respond to a sudden threat are being identified as neuroscience is beginning 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. This response is triggered when the amygdala activates the same region of the brain that controls other powerful unconscious urges including sex, thirst, and hunger: the hypothalamus. The release of adrenalin and other signals set our heart racing, muscles twitching, and body sweating to battle or to flee.

Danger signals shoot through high speed pathways to the brain’s threat detection circuits rather than engage 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 from our eyes is transmitted to the cerebral cortex at the back of the brain. Here complex analysis enables us to interpret the shifting patterns of light and shows cast on our retinas as objects in space, with color, dimension, motion, and identity. But, this sophisticated visual processing takes time–too much time to dodge a left hook, for example. 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!

New research is finding that different types of threats engage different threat detection circuits. A mother rat snapping aggressively to protect her young, for example depends on circuits in the ventral premammilary nucleus (PMv) of the hypothalamus, but a different type of threat, aggression related to social defense for example, passes through a different hippocampal relay point, the dorsal premammillary nucleus. Genetic and environmental factors will also influence the strength of these different circuits in different individuals, as will hormonal fluctuations, chronic stress, and many other factors.

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 are they gang members in combat? But neither apathy nor confusion is what those riders on the Metro train experienced. 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 is not a matter of bravery or cowardice or apathy; it is a matter of deadly 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. Instead, the passengers tried to appease the robber with cash. 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 Red Line is misguided. No fault should be leveled against any individuals on that train. They did as their brain and evolution has equipped them to do.

References

Dvorak, P., “Hear the roar of armchair Metro heroes, The Washington Post, July 10, 2015, p. 9A.

http://www.pressreader.com/usa/the-washington-post1047/20150710/281517929793203/TextView

Hermann, P., “Horrified passengers witnessed brutal July 4 slaying aboard Metro car. The Washington Post, July 7, 2015. http://www.washingtonpost.com/local/crime/victim-in-metro-slaying-stabbed-repeatedly-during-robbery-on-train/2015/07/07/8dd09132-249b-11e5-b72c-2b7d516e1e0e_story.html

Motta, S.C. et al., (2013) Ventral premammillary nucleus as a critical sensory relay to the maternal aggression network. Proc. Natl. Acad. Sci. USA August 27, 2013 110:14438-43.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3761625/

Shang, C., et al., (2015) A parvalbumin-positive excitatory visual pathway to trigger fear responses in mice. Science, June 26, 2015, 348:1472-7.

Adapted from: Fields, R.D. Why Nobody Intervened in the July 4 Metro Murder. Scientific American Guest Blog: July 17, 2015

http://blogs.scientificamerican.com/mind-guest-blog/why-nobody-intervened-in-the-july-4-metro-murder/

Why We Snap, by R. Douglas Fields http://www.penguinrandomhouse.com/books/316682/why-we-snap-by-r-douglas-fields/