For most people with epilepsy, not getting enough sleep will increase the chances of their having a seizure. Sleep is a rather mysterious state which interacts with epilepsy in a number of ways. It's not known why not having enough sleep should have any effect on seizures. Now researchers in Australia have found evidence for what's going on, by carrying out an electrical and magnetic study of the brains of people with epilepsy.

The researchers, led by Dr RA Badawy in of the University of Melbourne, Australia, studied 30 people with epilepsy and 13 controls without epilepsy. To allow for differences in types of epilepsy, the epilepsy participants included 15 with generalised epilepsy (seizures throughout the whole brain) and 15 with focal epilepsy (seizures starting on one side of the brain only). None of the patients, who were all newly diagnosed with epilepsy, were taking any AEDs. They were all adults, aged between 16 and 77 years.

Using EEG and transcranial magnetic stimulation (TMS: a technique in which the electrical activity of the brain is stimulated by a powerful magnet held close to the skull) they measured the response of the patient's brain to a series of electro-magnetic pulses. They made this measurement twice for each patient, once when the patient had had normal sleep, and once when they were sleep deprived, having been awake for at least 20 continuous hours in the previous 24.

In their report, published in the September edition of Neurology, the research team found there was a significant difference in response to TMS in both sides of the brains of people with generalised epilepsy when they were sleep deprived. A similar but smaller change was seen in patients with focal epilepsy, but only on the side of the brain where the seizure focus was. The other side showed only small changes, as did the brains of controls.

The EEG study also showed an increased number of seizure-like electrical brain patterns after sleep deprivation, with the same pattern of distribution as the TMS response: both sides of the brain in generalised epilepsy patients, only one side in focal epilepsy patients (the one where seizures happened) and no change in controls and in the opposite side of focal epilepsy patients.

This study has for the first time found direct evidence of a change in excitability of the outer part of the brain (the grey matter) due to sleep deprivation. A detailed analysis of the response type suggests that this is due to a failure of inhibitory signalling rather than to an enhancement of excitatory signalling. The effect also depends on what sort of epilepsy the person has. This was expected because people with generalised epilepsy are much worse affected by lack of sleep than people with focal epilepsy.

Epilepsy Research UK is funding a study of using TMS to explore the electrical and magnetic properties of the seizure focus (the area of the brain where a seizure starts). Read more about it here