ONE morning Paul Whiting woke up and couldn鈥檛 remember his way to work. 鈥淚t was frightening,鈥� he says. 鈥淚 had to go downstairs and ask my wife.鈥� As it turns out, the 57-year-old from Tiverton in Devon, UK, was in the midst of a brain seizure, although his only symptom was memory loss. This is typical of a form of epilepsy known as transient epileptic amnesia. First characterised in 2007, TEA is now challenging our understanding of memory.
For years, there have been anecdotal reports of the condition. Then, a year and a half ago, Chris Butler at the University of Edinburgh, UK, and his colleagues published the first systematic examination of a large group of people with TEA (Annals of Neurology, ). The study confirmed that TEA is indeed a form of epilepsy and that it can be treated with the same anticonvulsant drugs.
Now, further studies of people with TEA are challenging conventional ideas of how memories are formed, which could be important in identifying tests and possible treatments for Alzheimer鈥檚 and other memory disorders.
Advertisement
Butler鈥檚 2007 paper showed that, unlike the standard form of epilepsy, which often causes people to lose consciousness and impairs other brain functions, a typical hour-long TEA seizure only affects memory. 鈥淭here was one chap who woke up and didn鈥檛 remember that his brother had died a couple of days earlier,鈥� says Butler.
In other respects, people undergoing a TEA seizure function well. 鈥淭hey can get up, brush their teeth, even win a hand of bridge,鈥� says Butler.
鈥淧eople having a seizure function normally: they can brush their teeth or even win a hand of bridge鈥�
The observation that other brain functions seem unimpaired led Butler to suggest that only the hippocampus 鈥� an area of the brain involved in memory 鈥� is affected by the seizure. Yet combine this with another of Butler鈥檚 2007 findings, and things don鈥檛 quite add up.
As well as the temporary amnesia, Butler鈥檚 team found that around 70 per cent of people with TEA, including Whiting, lost memories of distant events, while some lost memories of previously familiar places. Both problems persisted after the seizure had ended. 鈥淭here are places that I鈥檝e done work, and as far as I鈥檓 concerned I鈥檝e never been there,鈥� says Whiting. 鈥淚t鈥檚 not just cloudy, it has completely gone. I also don鈥檛 remember one of my daughters鈥� weddings.鈥�
If Butler鈥檚 assumption that TEA only affects the hippocampus is true, these findings are surprising, as standard theories of memory have it that the hippocampus is only involved in retrieving short-term memories. To resolve this seeming contradiction, Butler suggested that the hippocampus might play a role in retrieving long-term, as well as short-term, memories.
Now Butler and his colleagues have investigated further. Brain scans of 41 people with TEA and 20 healthy volunteers revealed that the hippocampus is slightly smaller in people with TEA, further supporting the idea that TEA seizures affect mainly the hippocampus. However, the size of the hippocampus did not differ in people with TEA who had long-term memory problems and those who didn鈥檛, suggesting that the long-term memory problems are caused by the seizures (Brain ().
of University College London agrees that our understanding of memory may need adjusting, but cautions that the seizures might be affecting other brain areas connected with long-term memory after all. Butler agrees that further studies are needed to confirm this.
If the hypothesis that the hippocampus plays a role in long-term memory proves correct, it would chime with recent studies that found other unexpected roles for the region, such as enabling people to 鈥渞elive鈥� past events and imagine the future.
Demis Hassabis, also of University College London, says Butler鈥檚 results are preliminary but intriguing. Because TEA often only becomes apparent upon waking, he suspects that seizures may interfere with sleep and therefore with the memory consolidation process that occurs during sleep. This might partially explain memory loss due to TEA.
Butler鈥檚 works also raises the possibility that conventional epileptic seizures wipe memories too , a problem hitherto blamed on confusion or medication.
Whiting, meanwhile, has found a silver lining: 鈥淚 can watch films time and time again,鈥� he smiles.
