* * *

The nadir of Hepola’s book happens in Paris, while she’s on a magazine assignment. She comes to in the middle of a blackout, having sex with a stranger, leaves the room, then goes on a wild hunt for her purse, which it turns out she left in her own room. There’s also a part where a sleazy hotel concierge takes advantage of her after she asks him for help.

“As I lay in my hotel bed, covers pulled up to my neck, I felt the gratitude of a woman who knows, finally, she is done,” Hepola writes of that night. “But I drank on the plane ride home. And I drank for five more years.”

Blackouts were once thought to be the domain of alcoholics alone, a risk factor that amounted to a sort of input/output equation: If blackout, then alcoholic. For that we have E.M. Jellinek to thank—the “father of the modern disease model of alcoholism,” according to Aaron White, the senior advisor to the director at the National Institute on Alcohol Abuse and Alcoholism (NIAAA). In a survey of Alcoholics Anonymous members, Jellinek found that many reported having frequently blacked out, and a link between blackouts and alcoholism became entrenched. Wrongly so, White says. Blackouts are commonly seen in alcoholics, in part because people can build up a tolerance to some of the other negative consequences of alcohol—loss of balance, for instance—but not so much to its effects on memory. Still, White says, “anyone can black out at least once, if you drink in the right way—or the wrong way.”

In a survey he did at Duke University, 51 percent of students who reported ever having consumed any alcohol had experienced at least one blackout. But there have been no more comprehensive population surveys on how common they are. “Blackouts have basically been ignored as a subject of study,” White says. “We don’t have any national data.”

A blackout can mean the total erasure of an entire chunk of time from a person’s memory, an occurrence known as an en bloc blackout. Or they might just forget bits and pieces, in a fragmentary blackout, or a brownout, as some call it. These are more common, White says. Either way, the memories are gone because they were never stored in the first place.

Even during a blackout, a drinker’s short-term memory is generally fine. She can carry on a conversation, though, like a human goldfish, she may quickly forget things and repeat herself. It’s episodic memory where alcohol gums up the works. These are the memories of events—what happened, but also where, when, and with whom. Alcohol impairs the encoding of these contextual memories, which happens in the hippocampus. “Your brain is sending information to the hippocampus, and it falls into a void,” White says. “The hippocampus doesn’t tie it together, or it skips a little bit.” After a fragmentary blackout, being reminded of some of that context might help someone remember what happened. After an en bloc blackout, one will need to rely on the memory of others.