The temporal lobe of the brain is highly involved in processing memories, recognising emotions, and understanding speech, all functions essential to everyday life. Surgery to correct seizures arising in the temporal lobe carries a risk of damage to memory function. Being able to predict who's likely to lose some memory function is important so as to be able to allow patients to take an informed decision about whether or not to have the surgery, and to counsel patients about memory loss.

However, it's not easy to predict which patients will be affected in this way, and the extent of any memory decline. The effect can depend on the cause of the epilepsy (e.g. disease or trauma), the extent and nature of the damage to the tissue (e.g. dead cells, abnormal distribution of cell types, damaged cell functioning), the types of seizures the person has, and their seizure frequency. There has been a great deal of interest among researchers to develop a method of predicting the likely extent of memory decline.

In a study published in the journal Epilepsia in November, scientists from the Institute of Neurology in London studied a group of 288 patients who had had surgery for temporal lobe epilepsy. A total of 125 patients had the operation on the right temporal lobe and 163 on the left. The researchers, led by Dr S Baxendale, used a mathematical model to find any correspondences between certain features of these patients' epilepsy and their memory outcome after surgery. These features included the age of the patient, whether their left or right temporal lobe was affected, their age when their epilepsy started, the underlying cause of their seizures and their level of memory function before surgery.

A quarter of all the patients in the study showed a significant degree of deterioration in their memory performance after their operation. The best indicator of this decline was having high level of ability before the operation. Other significant factors depended on whether the operation was in the right or left lobe. In patients who had right temporal lobe surgery, older age at the time of the operation and lower verbal IQ indicated poorer outcome. In patients who had left temporal lobe surgery, the presence of abnormal growth patterns in the white matter of the outer layer of the brain was significant.

The mathematical model these researchers were using correctly identified three-quarters of the patients at risk. This is a higher proportion than that achieved with a number of models developed by other research teams. The new model could therefore allow most patients who are at risk of a significant decline in memory after surgery to be successfully identified beforehand, making it a valuable tool to help patients make an informed decision about having the operation.

Epilepsy Research UK is currently funding a study investigating whether children with epilepsy experience this sort of memory loss after surgery. Children's brains have a greater capacity than adults' for re-organising and re-growing functionality after an operation, as they are still developing. Click here to find out more