※訳注：この記事でホッパー博士は、これまで"fear circuitry”（恐怖回路）としていたものを、"defense circuitry"（防御回路）と言い換えている。掲載当時(2015年）からの研究の進歩により、扁桃体（amygadala）が「恐怖」ではなく「防御」を司る機能だと判明したからだという。つまり、記憶が曖昧になったり消失したりすることは、「恐怖」による脳機能の障害ではなく「脅威」に対する脳の自然な「防御反応」だと。博士本人からその旨の説明を受け、新たな原稿（公開中）をいただいたのであらためて訳出する。

[Lead Text] In the midst of sexual assault, the brain’s defense circuitry dominates. The prefrontal cortex can be severely impaired, and all that’s left may be reflexes and habits.

Many victims of rape have described how they reacted - and did not react - while being assaulted. An article in the Harvard Review of Psychiatry shows that some basic responses have been programmed into human brains by evolution.

Bringing together the accounts of those who have been assaulted with the neurobiology of trauma can play an essential role in supporting healing and the pursuits of accountability and justice.

For example, freezing is a brain-based response to detecting danger, especially a predator’s attack. Think deer in the headlights.

As one woman said, “I didn’t say no, but I didn’t really know what to do. I just kind of froze.”

Freezing occurs when the amygdala - a crucial structure in the brain’s defense circuitry - detects an attack and signals the brainstem to inhibit movement. It happens in a flash, automatically and beyond conscious control.

It’s a brain response that rapidly shifts the organism into a state of vigilance for incoming attacks and avenues of escape. Eyes widen, pupils dilate. Hearing becomes more acute. The body is primed for fight or flight. But as we shall see, neither fight nor flight necessarily follows.

Simultaneously with the freeze response, the defense circuitry unleashes a surge of “stress chemicals” into the prefrontal cortex, the brain region that allows us to think rationally - to recall the bedroom door is open, or that people are in the dorm room next door, for example, and to make use of that information. But the surge of chemicals rapidly impairs the prefrontal cortex. That’s because, despite our dominant role on the planet now, we evolved as prey, and when a lion or tiger is upon us, stopping to think is fatal.

Indeed, no one understands better than the military that intense stress and fear impair our prefrontal cortex and capacity for reason.

When bullets are flying and blood is flowing, you had better have some really effective habit learning to rely upon. That’s why combat training is rigorous and repetitive - to burn in habits of effectively firing weapons, executing combat formations, etc.

But what if you’re being sexually assaulted and there’s no effective habit learning to fall back on?

What if you’re a woman and the only habits your brain cues up are those you’ve always relied upon to ward off unwanted sexual advances - like saying, “I have to go home now” or “Your girlfriend will find out”? Those phrases, and passive behaviors that go with them, may be your only responses, until it’s too late.

Countless victims of sexual assault describe just such responses. Too often police officers, prosecutors, college administrators, even friends and family think to themselves—and say out loud—“Why didn’t you run out of the room?” “Why didn’t you scream?”

But those who assume a functional prefrontal cortex - including many victims as they look back on what happened - passive habit responses can be baffling. They seem exactly the opposite of how they surely would - or should - have responded.

But when the defense circuitry takes over and the prefrontal cortex is impaired, habits and reflexes may be all we’ve got.

And if the defense circuitry perceives escape as impossible and resistance as futile, then not fight or flight, but extreme survival reflexes (which scientists call “animal defense responses”) will take over. These can activate automatically when the body is in a predator’s grip--and when, as half of rape victims report, we fear death or serious injury.

One such response is tonic immobility. In freezing, brain and body are primed for action. But in tonic immobility, the body is literally paralyzed by fear - unable to move, speak, or cry out. The body goes rigid. Hands may go numb.

Collapsed immobility is another. Heart rate and blood pressure suddenly drop, and the brain is deprived of oxygen. People feel faint and may even pass out.

To see what this looks like (and get a humorous break from this difficult topic), you can watch the YouTube videos that come up for “passes out on Slingshot ride”.

Some describe feeling “like a rag doll” as the perpetrator did whatever he wanted. Others describe feeling “sleepy”.

Too often, from precinct stations to courtrooms, victims are met with disbelief: How could it be rape if you were sleepy?!

Another, more common reflexive response is dissociation: disconnecting from the horrible emotions and sensations of such an intimate violation. Spacing out and feeling unreal, like in a dream. Or attention may narrow to a spot on the ceiling or sounds of the street below.

Unless someone is drugged or intoxicated into unconsciousness, eventually the brain’s defense circuitry will detect the attack and take over.

Most victims will freeze, if only briefly. Some will fight back, effectively. Some will resist in habitual passive ways. Some will suddenly give in and cry. Others will become paralyzed, become faint, pass out or dissociate.

Few who’ve experienced these responses realize that they are brain reactions to attack and terror.

They blame themselves for “failing” to resist. They feel ashamed. (Men especially may see themselves as cowards and feel like they’re not real men.)

They may tell no one about these responses, even during an investigation. Sadly, many investigators and prosecutors still don’t know about all or some of these brain-based responses.

None of these responses - in women or men - entail consent or cowardice.

None are evidence of resistance too insufficient to warrant our respect and compassion.

They are responses we should expect from brains dominated by the defense circuitry (just as we should expect fragmented and incomplete memories).

Finally, they are responses we should expect in every culture. Evolution programmed these responses into our brains long before we were sophisticated enough to create cultures, or confused enough to misjudge victims with culture-based expectations of how women and men “should” respond while being sexually assaulted.

May the day come when everyone who knows someone who has been sexually assaulted - which is all of us, whether we know that yet or not - understands these basic ways that our brains can react to such attacks and uses this knowledge to foster healing and justice.