In light of the John Darwin affair, Claire O'Connellexplores various types of amnesia and wonders what factors prompt a return of memory
When prison official and former teacher John Darwin walked into a police station in central London on December 1st and told them he thought he was a missing person, he sparked off a saga that gripped headlines around the world.
Darwin disappeared in March 2002 when he went kayaking in the North Sea at Seaton Carew. Despite the water that day being reportedly as smooth as a millpond, Darwin was not found. His wrecked kayak washed up close to his home six weeks later, and in 2003 he was declared officially dead.
On resurfacing in 2007, Darwin claimed to be suffering from amnesia, with no recollection of the past seven years. But even before his story capsized and left him facing charges of life insurance fraud, his reported memory loss and subsequent recovery seemed a little fishy, as it didn't quite fit the bill for reliably documented cases of amnesia.
Memory loss has long been a staple of fictional characters, and has driven storylines on screen for almost a century, with recent examples including 50 First Dates and the Bourne series. But with few exceptions, film portrayals of amnesia tend not to be plausible.
In reality, amnesia is often a frustrating, distressing and disempowering experience, according to Ian Robertson, professor of psychology at Trinity College Dublin's Institute of Neuroscience. The most common form of amnesia is the type that tends to develop in Alzheimer's disease or in ageing, where there is a difficulty in laying down new memories, he explains.
So you make the same observation or have the same conversation as you had with someone a short time before. You don't remember what you had for lunch or where you were yesterday. The jargon for that is anterograde amnesia, which is where you don't lay down new memories and, as a result, there's a gap. Older people who develop this, for example, reminisce in great detail about what happened when they were younger, but they have a blank when it comes to more recent things because laying down new memories is not working properly. An area of the brain called the hippocampus is central to laying down new memories, and is often affected in amnesia. It's like the checking desk in a library, and incoming memories are processed there before being sorted and archived. If the hippocampus is damaged or stressed, memory loss can occur.
In some cases the hippocampus can become temporarily stunned, says Robertson, and a person can suffer transient global amnesia. It's as if the sorting desk of the brain's library has briefly gone on fire, and memories that were waiting to be shelved have been wiped out.
"If you were to talk to me tomorrow, me having had transient global amnesia today, that 24 hours would be a blank to me because my hippocampus has been temporarily not working," says Robertson, who notes that the condition can crop up in people who have had a bang on the head or concussion following an accident.
People are sometimes forced to try to remember what happened after the accident and they won't get that fully back because the apparatus for laying down new memories wasn't working, he says.
Transient amnesia can also happen following severe stress, where the hippocampus becomes flooded with a brain chemical called glutamate, which is used in normal brain function but in large quantities can be toxic to the sensitive cells in the memory apparatus.
It's a rare condition but it does happen that someone can become amnesic in that sense, he says. But, thankfully, transient global amnesia tends to be reversible. However, if the hippocampus has been irreversibly damaged following severe brain injury or stroke, the prognosis is rather less encouraging. Unfortunately, if the hippocampus gets destroyed it tends to be lifelong, he says. We would have to hope that with stem cells there might be the possibility of regenerating in the brain but at the moment it's a very gloomy prognosis if you have amnesia of that kind.
However, Robertson notes that strides are being made to help compensate for memory deficits. A recent study at Cambridge asked people with amnesia to wear a small camera and record events from their perspective during the day and then look at the record of what they had done. It really seemed to help. It didn't cure their amnesia but it improve their ability to recall, because amnesia seldom is 100 per cent, there's often some capacity to remember, although in a few terrible cases there isn't.
However, someone claiming to have forgotten everything that happened for a long period and then regaining the power to lay down new memories is a story Robertson would not buy straight off.
If you can start talking intelligently about having lost your memory for the past few years that implies you have a certain memory now and you are not suffering from anterograde amnesia, he says. So he would want to exclude a whole lot of other psychiatric and psychological factors before he'd consider he had discovered some amazing new function of the memory, he says.