A 38-year-old British patient has recorded almost no new memories since undergoing a root canal in 2005. (iStock)

The man, called only “WO” by his physicians, woke up on the morning of March 14, 2005, at his military post in Germany. He headed to the gym, where he played a 45-minute round of volleyball, then returned to his office to answer a backlog of e-mails. In the afternoon he went to his dentist for a routine root canal treatment. He clambered into the reclining chair, donned a pair of tinted glasses, felt his mouth go numb as the dentist inserted local anesthetic.

Every day since, no matter what the actual date happens to be, WO wakes up thinking it’s the morning of March 14, 2005, believing he is still in Germany and that this is the day of his dentist appointment. His life is something of a “Groundhog Day” in reverse — while the rest of the world moves on, WO is the only person who isn’t aware of time passing. Starting from that moment in the dentist’s chair a decade ago, he hasn’t been able to remember almost anything for longer than 90 minutes. Then he forgets it, a switch flips, and he’s back to March 14, 2005, once more.

The case, which WO’s doctors Gerald Burgess and Bhanu Chadalavada dissect in a study published in the journal “Neurocase,” is indeed a medical mystery.

The patient, a 38-year-old member of the British Armed Forces, had an unremarkable personal and medical background. He was a happy husband and father of two children, was in good standing at work, his only health complaints were the fairly typical aches of middle age — back pain, hypertension.

There was nothing about WO or the ordinary, hour-long root canal procedure to indicate that something catastrophic was happening. His doctors aren’t even absolutely sure that the operation is what triggered his memory loss.

But the main thing that continues to captivate and confuse doctors most is this single, inexplicable fact: There doesn’t seem to be anything wrong with his brain.

[How a brain treatment for OCD turned a man into a Johnny Cash fanatic]

WO has been tentatively diagnosed with anterograde amnesia, the loss of ability to form new memories after a traumatic event. (It’s more or less the condition that Drew Barrymore has in the movie “50 First Dates.”) Much of what we know about this condition comes from the experiences of Henry Gustave Molaison — known to most of the world as H.M. until his death in 2008 — who underwent a flawed brain operation to treat his epilepsy in 1953 and woke up suddenly unable to learn anything new.

The operation turned out to be, in the words of Molaison’s surgeon William Beecher Scoville, a “tragic mistake.” It stripped Molaison of his hippocampus, the seahorse shaped region of the brain that is effectively the mind’s stenographer, responsible for capturing events and sending them away into long-term storage. Without it, Molaison had no transcript of his life after age 27. His personality hadn’t changed, or his ability to go about everyday tasks. He was even capable of acquiring new skills. But he had lost the ability to remember episodes and string them into a narrative. He was forever adrift in the present.

What WO now experiences seems similar. Though his doctors describe him as “managing” his daily life, he is completely dependent on an electronic diary that reminds him of what he’s doing and what has happened in the 10 years since his last new memory. Every morning he checks his computer for a list of life events he should be aware of — marriages, deaths, his children’s birthdays. Some of them, like the loss of a beloved pet, continue to surprise him.

Stranger still is WO’s relationship to his condition, which he describes almost as if he is simply repeating what he’s been told about himself. He will refer to his notes, then say, “I know I have a memory problem,” or, “I think it’s March 2005, but it’s not,” his doctors report in their study.

But unlike in Molaison’s case, there doesn’t seem to be any structural reason for WO’s illness. Brain scans show that his hippocampus is entirely intact. And unlike Molaison, WO doesn’t seem capable of learning procedural skills, which are processed in a different part of the brain. Burgess told the BBC that when WO was asked to complete a complex maze he had already navigated three days earlier, he approached the puzzle as if for the first time.

“It was like a déjà vu replica of the same errors — he took the same time to relearn the task once more,” Burgess, a psychologist at the University of Leicester, said.

Because there was no structural explanation for WO’s memory loss, his was initially diagnosed with “psychogenic” amnesia, a disorder caused by psychological stress rather than a physical cause.

But that explanation didn’t seem to fit either. For one thing, there was no obvious trauma in WO’s past that might have triggered the illness — though he is a veteran of the first Gulf War and had just returned from his grandfather’s funeral, he has no history of mental illness and has typically been in good emotional health. For another, psychogenic memory loss is usually a “coping mechanism” that prevents patients from recalling painful memories in their past — not forming and recalling new ones.

WO’s condition is distinct from both those ailments, his doctors concluded. Its cause isn’t structural or emotional but something else entirely. The stenographer in his hippocampus is still recording new information, but it’s as if the memories are being written in sand. Every hour and a half the tide comes up and washes them away.

The process that, in a normally functioning brain, would turn that sand into cement is called “consolidation.” It happens not in the hippocampus but among synapses — the tiny junctions between nerve cells across which the signals in our brain travel. When memories are consolidated into the long term, proteins are produced that restructure synapses, establishing a new connection that allows the brain to recall the route of that initial impulse. Studies on the synthesis of these proteins in rats have found that blocking the process prevents the animals from learning to avoid painful experiences.

Consolidation usually takes about 90 minutes — the same amount of time that WO’s new memories last — making it a compelling explanation for WO’s problem.

A consolidation explanation also seems to fit five other cases of unexplained anterogade amnesia that Burgess and Chadalavada found in the literature. Like WO, the five patients in those cases also experienced amnesia after some sort of medical emergency — the doctors speculate that the patients may have a genetic predisposition that was triggered by an episode of physiological stress.

But that’s just a theory. For now, it’s a mystery why a routine root canal seems to have cost WO his ability to record any new memories in the past decade.

“That’s the million pound question,” Burgess told the BBC. “And I don’t have an answer.”

In the 10 years since that fateful trip to the dentist, as his memories are repeatedly, relentlessly eroded at 90 minute intervals, WO has been able to retain just one new fact: The knowledge of his father’s death. WO doesn’t recall the moment his father passed, nor the tireless bedside vigil that preceded it. But something — his intense emotional connection to his father, or perhaps the fact that it was the only thing WO thought of during the 90-minutes after it happened — keeps his awareness of the event alive.

It’s the sole piece of driftwood WO has clung to as the tide washes everything else away.