In the classic movie "Memento," Guy Pearce’s character Leonard awakes each morning with a blank slate, unable to form new memories due to a condition called anterograde amnesia, which he developed following a blow to the head. This is fictional, but Lenny’s situation isn’t unique to Hollywood. Described in the journal Neurocase is the remarkable story of a British man who, since receiving an anesthetic 10 years ago, can only remember things for up to 90 minutes.

Day in, day out, the man wakes up thinking it’s March 14, 2005, the date his fascinating story began. Thirty-eight-year-old William O. went in for a dental procedure that required a local anesthetic, but after getting into the dentist’s chair, his memory is totally blank. His situation is so unusual that researchers have described it as new to science.

“One of our reasons for writing this individual’s case was that we had never seen anything like this before in our assessment clinics, and we do not know what to make of it,” lead author Dr. Gerald Burgess from the University of Leicester said in a statement.

Prior to the memory loss event, William was a fit and healthy member of the British Armed Forces. He had no history of psychiatric or mood problems, nor were there any records of mental illness in his family. At 1:40 p.m. on March 14, he went to the dentist for a root canal treatment for which he was given a local anesthetic. After the procedure was finished, the man couldn’t get up and was described as “vacant.” By 5 p.m. that same day, he hadn’t improved and so was taken to the hospital.

For a month following initial admission, he could only remember new things for about 10 minutes, after which the memories vanished. His personality didn’t change, and he was fully aware of who he was and everything up to the incident. Over time, his episodic memory slowly extended, but today he can still only remember events for about an hour and a half, and every day he wakes up believing it’s still 2005 and that he needs to get to the dentist. He only knows differently because he and his wife have put together notes on his smartphone for him to read each morning.

William has a condition called anterograde amnesia, which often manifests from damage to the region of the brain critical to learning and memory, the seahorse-shaped hippocampus. It was thought that he could have had a reaction to the anesthetic that resulted in neurological injury, but several different types of brain scans have failed to find any visible abnormalities.

While researchers are still completely flummoxed, they have put forward a few different ideas, none of which point the finger at the anesthetic or the dental procedure. One is that it could be an unusual form of psychogenic amnesia, which is where patients experience memory loss following a traumatic life event, BBC Future explains. But according to the report, William hadn’t suffered any such events, and he was emotionally stable.

Another possible explanation is that he may have a deficiency in protein synthesis, a process needed for the restructuring of nerve cell connections, or synapses, that permit the flow of information. Without the ability to alter and strengthen these structures following an event, memories cannot be consolidated and therefore fizzle away. What’s most convincing is that this process takes around 90 minutes, which is how long he is able to retain new memories.