Editor’s Note: Robert Sapolsky is a professor of biology, neurology and neurosurgery at Stanford University. He is also the author of “Behave: The Biology of Humans at Our Best and Worst.” The opinions expressed in this commentary are his own. View more opinion articles on CNN.
Thursday was one remarkable day for neuroscientists. Study the brain and you work in obscurity on obscure brain regions with obscure functions. And suddenly, one of those regions was front-and-center in the drama playing out in Washington.
America sat mesmerized, listening to the testimony of Christine Blasey Ford. In a voice constricted with emotion, she described the nightmare of being sexually assaulted at 15 by a high school student she alleged to be the drunken Brett Kavanaugh. One winced, hearing the painful details. Amid this firestorm, the simple question we all ponder is anything but simple – did this actually happen?
At first glance, one feature of Ford’s testimony seemingly weakens her credibility. Amid the claims of clear, detailed memories of the assault, she cannot remember straightforward facts such as where this happened and on what date. For many, this is grounds for skepticism.
Sen. Diane Feinstein gave Ford a chance to address this, asking how, amid those basic details she couldn’t recall, she was so sure it was Kavanaugh. Ford, with a doctorate in psychology, answered, “The same way that I’m sure that I’m talking to you right now. It’s – just basic memory functions. And also just the level of norepinephrine and epinephrine in the brain that, sort of, as you know, encodes – that neurotransmitter encodes memories into the hippocampus. And so, the trauma-related experience, then, is kind of locked there, whereas other details kind of drift.”
Which is when the neuroscientists perked up. Ford had mentioned the hippocampus, a brain region located just below the cortex in the temporal lobe, beloved by many a neuroscientist (myself included). The hippocampus is central to the formation of new memories – specifically explicit, declarative ones about facts and sequences of events (versus an implicit memory of, say, how to ride a bicycle). Extensive research has revealed the workings by which the hippocampus forms new memories.
But Ford did not merely cite the hippocampus; instead, she cited a particular feature of its function, reflecting the fact that we don’t automatically, indiscriminately commit everything to memory. Instead, we remember the big things – where we were on 9/11, not 9/10.
During moments of highly aroused stress and fear, we develop a tunnel vision of memory. This was shown in a classic 1994 study by Larry Cahill, James McGaugh and colleagues at the University of California, Irvine, where volunteers were told a 12-sentence story. For half, it was mundane – a boy and his mother walk through town, on their way to visit his father at his workplace, the hospital; they cross the street, reach the hospital, where the boy observes the goings-on.
For the remaining subjects, the story diverged – the boy and his mother are on the way to visit the father, and while crossing the street, the boy is critically injured by a vehicle; he is rushed to the hospital where staffers struggle to save his life. The two versions were identical in the first four sentences, and similar in the final four. It was in the middle four that only the second group heard of the horrific accident.
A week later, subjects’ memory of the story was tested. Recall of the story involving the accident was better than for the mundane story. Crucially, accurate recall was only enhanced for those four central sentences concerning the emotionally disturbing events; memory about the mundane beginning and end were no better than in the control subjects. In other words, it is only the most pertinent memories of a trauma that are indelible. Whose hand it was covering your mouth is there forever; the date and whose house it was fades into irrelevance.
(Ford also summarized how this works. Extreme stress triggers the release of the hormone epinephrine – also known as adrenalin – along with the closely related brain chemical norepinephrine. It is these that tell the hippocampus that all hell is breaking loose and it better remember the parts that matter.)
Which raises another feature of this drama. There’s Ford, educated, articulate, seemingly distraught, saying: This happened. And there’s the educated, articulate Kavanaugh, seemingly outraged, saying: It did not.
One more interesting fact about hippocampal function: as shown when one drinks too much and wakes the next day with no memory of the night before, a sure way to keep the hippocampus from filing away memories of events is with alcohol. Thus, rather than a passionately stated “She said/He said,” we could have a “She remembers/His brain never consolidated those memories in the first place.”
There are few means to distinguish between the indignant response to being accused of something you did not do, versus the response to being accused of something you can never remember. That needs to be factored into our thinking about this hugely consequential crossroads where we sit.