'Transient' amnesia can occur after sex

His wife was in long-term care, so he decided to go on a cruise.

On the cruise, he met someone. They began an affair.

Back on land, the pair found themselves entwined in the backseat of a car. Out of nowhere, the man turned to his new partner and asked, "Who are you? What are we doing here?"

Baffled, the woman drove him to a nearby hospital. Eventually, he was diagnosed with a rare disorder called TGA — Transient Global Amnesia.

The unnamed cruise ship traveller's misadventures were first noted by the pair of neurologists who coined the term, TGA.

Sufferers of TGA — generally people over 50 with a history of migraine — suffer a constriction of blood in the hippocampus. Scientists now believe that such spasms in the back of the brain can hamper memory. There are a long list of activities that can trigger TGA — sudden immersion in hot or cold water, physical exertion, emotional shock and, yes, sex. Typically, the event occurs shortly after orgasm. It is usually preceded by a headache.

It is a rare disorder. According to a 1987 study, it occurs to 23.5 people out of 100,000 in the United States. All of those included in that measure were older than 50.

But the light it sheds on the operation of memory is of immense interest to neurologists, like Dr. Louis Caplan of Harvard Medical School.

"(Sufferers) behave normally during the episode even though they're not recalling it. It's a little bit like having a tape recorder on," said Caplan. "(During an episode) the tape recorder's not on, you're not recording anything, but you can still function normally."

Patients of Caplan's have variously taught a physics class, given an interview and performed in a chamber orchestra while in the midst of a TGA episode.

Caplan recalled another of his patients walked out of a bathroom at work, ran into his personal assistant of nine years, and wondered aloud who the person was.

While that particular patient had temporarily lost the ability to form new memories, he'd also lost the last 10 years. His wife figured that out by asking him how old their children were.

"As time went on, that period of retrograde amnesia shrunk. Eventually, it only stretched back to a couple of hours before the incident occurred. That's the typical thing," said Caplan.

Essentially, neurologists regard TGA as a benign affliction, something curious, though Caplan concedes it's jarring to the sufferer while they're in the midst of it. Those struck by TGA rarely feel its effects twice. And even a single incidence is so unusual that Caplan advises those in middle- and late-life to put it out of mind.

"It's rare enough that you don't want to worry people," said Caplan.