In this Research Blog, consultant neurologist and BRC Senior Research Fellow Professor Arjune Sen shares his clinical experiences of epilepsy-related memory loss and discusses the latest research aiming to improve our understanding of the link between epilepsy and memory.
Every week in my clinic I meet dozens of people living with epilepsy. Epilepsy is, of course, an umbrella term for over 40 conditions affecting people across their lifespan, each with a broad range of symptoms, treatment pathways, prognosis and varying impact on quality of life. As such, no two people with epilepsy are ever the same. That is what makes it so interesting! One concern that a lot of the people frequently ask me about is the impact of epilepsy on their memory. Sometimes this can be of greater impact than the seizures themselves, as while the seizures are episodic, the memory impairments can be present all the time.
Memory is the process of taking in information from the world around us, processing it, storing it, and later remembering that information, sometimes many years later. There are many different types of memory, including learning what words mean, where we have put something, and how to complete certain skills such as swimming or riding a bike. More complex types of memory include ‘spatial memory’ – how we get from A to B – and ‘autobiographical memory’, which allows us to recall and even ‘re-live’ personal events or episodes from our past. Memory is a complex function, involving many different areas of the brain, which can be affected when we have a condition that affects the brain.
But how exactly does epilepsy impact memory? Epilepsy may occur due to structural changes in the brain. If these structural changes are in an area of the brain that is normally used in the processes associated with memory, such as the hippocampus, then this may have consequences for memory. The disruptions that seizures cause to normal brain activity may also play a role in disturbing memory. For some people with epilepsy, their antiepileptic medication may also have a negative impact on their recollection, although this is less commonly seen with newer drugs.
One element of cognitive function that may particularly impact people with temporal lobe epilepsy is accelerated long-term forgetting (ALF). ALF describes what happens when memories appear to be taken in, processed and stored, but are only retained for short intervals of time: days, weeks, or perhaps even less. Such difficulties may not be easily picked up by conventional neuropsychometric testing, but they have a massive impact on day-to-day life.
While the links between memory and epilepsy have been recognised for a long time, we are now seeing several new and important developments. Over the last century there have been tremendous advances in healthcare, and, as a result of this, populations are ageing in the UK and across the world. The incidence of epilepsy is greatest in older populations and dementia is, generally speaking, a disorder that is associated with ageing. Despite this, we are only now appreciating how important epilepsy in older people and the links between epilepsy and dementia might be. With populations ageing three times more quickly in low to middle income countries this is a global problem.
In the past few years we have learnt that there is a bidirectional relationship between epilepsy and dementia. If you have dementia you are more likely to have seizures and many of these seizures may be unrecognised, potentially contributing to the cognitive impairment. We are exploring, therefore, whether anti–epileptic medication may benefit memory in people with dementia who have not had a seizure.
People with epilepsy may, at the onset of their seizures, note an ‘initial hit’ to their memory. It was thought that subsequent decline paralleled normal ageing, but this is not likely to be the case as seizures, status epilepticus, head injuries, changes in medication and comorbidities can all influence cognitive trajectory.
Importantly, we can adjust the trajectory as well. For example, recent data has shown that mid-life vascular risk factors can contribute to late onset epilepsy. Things like keeping physically active, not smoking, and eating a healthy, balanced diet may help maintain cognitive function, whether someone has epilepsy or not. Good sleep hygiene is so important to try and prevent seizures, as well as helping to improve memory performance. It has been shown, for example, that a period of sleep following learning can significantly improve memory performance compared to without sleeping.
Things are now moving quite quickly, which is just as well because there is a lot of important work to do. If we want to provide the best possible clinical management for people with epilepsy, we need to better understand the complex interwoven relationship of epilepsy with memory. The only way we can do this is through increased research support in this chronically underfunded area. We need, for example, to include older people with epilepsy in clinical trials and prospectively examine memory and other comorbidities in people with epilepsy. Only through further research, will we be able to ensure that fewer peoples’ lives are interrupted by epilepsy and its associated memory difficulties.
– Professor Arjune Sen