Dentistry has its hazards

One morning in March of 2005, William, a British soldier stationed in Germany, woke up and headed to the dentist for a root canal. Ten years have passed, and yet upon waking every morning since that day, William still believes it's March of 2005, that he is a British soldier stationed in Germany, and that he will soon be headed to the dentist for a root canal.

Something, in other words, happened between the time the surgery began and the time it ended — something that has prevented him from forming any long-term memories since the day of his dental surgery. When he forms new memories, they now only last about 90 minutes, according to the case report his medical team recently published in the journal Neurocase...

On a Monday morning in March of 2005, he woke up, went to the gym, stopped in at his office to take care of some emails, and went to the dentist. “I remember getting into the chair and the dentist inserting the local anaesthetic,” William told Robson. It's the last thing he remembers...

While in the hospital, his memory improved a bit, so that he had a "90-minute span of awareness," but it has not improved in the ten years that have passed since then. "He wakes up believing that he should still be in the military, stationed abroad," the case report authors write. "Every day he thinks it is the day of the dental appointment."

Like something out of Memento, his wife has entered a guide to his present life in the notes section of his smartphone, titled “First thing — read this." There, he learns every day what happened to him that day at the dentist, and that his children have now grown into young adults...

Dr. Gerald H. Burgess, a clinical psychologist at the University of Leicester and one of the co-authors of the case report, does have a theory, outlined in the BBC write-up of the case:

Once we have experienced an event, the memories are slowly cemented in the long term by altering these richly woven networks. That process of “consolidation” involves the production of new proteins to rebuild the synapses in their new shape; without it, the memory remains fragile and is easily eroded with time. Block that protein synthesis in rats, and they soon forget anything they have just learnt. Crucially, 90 minutes would be about the right time for this consolidation to take place – just as William starts to forget the details of the event. Rather than losing its printing press, like Molaison, William's brain seems to have simply run out of ink.

http://nymag.com/scienceofus/2015/07/man-who-lost-his-memory-at-the-dentist.html

Burgess GH, Chadalavada B. Profound anterograde amnesia following routine
anesthetic and dental procedure: a new classification of amnesia characterized by
intermediate-to-late-stage consolidation failure? Neurocase. 2015 May 15:1-11.
[Epub ahead of print]

Abstract

Anterograde amnesia caused by bilateral hippocampal or diencephalon damage manifests in characteristic symptoms of preserved intellect and implicit learning, and short span of awareness with complete and rapid forgetting of episodic material. A new case, WO, 38-year-old male with anterograde amnesia, in the absence of structural brain changes or psychological explanation is presented, along with four comparison cases from the extant literature that share commonalities between them including preserved intellect, span of awareness greater than working memory, and complete forgetting within hours or days following successful learning, including notably for both explicit and implicit material. WO's amnesia onset coincided with anesthetic injection and root canal procedure, with extended vasovagal-like incident. The commonalities between the five cases presented may suggest a shared biological mechanism involving the breakdown of intermediate-to-late-stage consolidation that does not depend on the structural integrity of the hippocampi. Speculation on the mechanism of consolidation breakdown and diagnostic implications are discussed.