Guest editorial: Insights into epilepsy

Epilepsy: a window into the brain? by Michael Marshall

Epilepsy is possibly the strangest, and surely the most varied, of all the neurological disorders. Its sufferers experience repeated 'seizures'; interruptions to their conscious life. A seizure often begins with strange sensations such as unreal smells or strong emotions, often fear. As it develops, the patient may behave strangely, walking in circles, talking nonsensically or even undressing themselves. In severe cases, they are rendered unconscious and undergo violent convulsions.

Virtually every conceivable neuropsychological symptom has been reported in connection with epileptic seizures. The seizures may cause headaches, vomiting, or the feeling of cold. Equally, they can produce temporary amnesia, powerful and seemingly causeless emotion, hallucinations and visions. The challenge of understanding this great diversity of experience is enormous, but it is also an opportunity, for in these seizures the structure and mechanisms of the brain are writ large for us to see.

Seizures are the result of paroxysmal over-discharge of cerebral neurones. The pioneering 19th century epilepsy researcher Hughlings Jackson described them as 'nerve-storms in the brain'. Neurones which typically fire in an orderly, regulated way suddenly erupt into action, expending energy wildly. Seizures can start up in any of the four lobes of the cerebral cortex, and recent evidence indicates that they may also begin in the deeper, sub-cortical brain.

Hardly surprising that the range of symptoms is so vast! A seizure in any region of the brain will interfere with that area's functions, perhaps halting them altogether. For example, if a person experiences a seizure in their memory centres, their memory could be affected. In this way, epilepsy can reveal a great deal about the workings of the brain.

The most common site of an epileptic seizure is the left temporal lobe, one of the brain regions most heavily involved in learning and memory. As with all forms of epilepsy, the range of possible symptoms is wide. But there are some that are peculiar to the temporal lobe. And some of them can be traced to that lobe's involvement in memory.

In many temporal lobe seizures, the first symptom is a strong sense of déjà vu. We have all experienced déjà vu; the strange conviction that we have done exactly this same thing before, that everything is a repeat of something that has gone before. Fans of science fiction movie The Matrix can relax; it is not a glitch in the universe!

One of the things the temporal lobe can do is to flag things as 'familiar', effectively putting a note on something that reads 'You've seen this before and know it well'. If this mechanism is activated incorrectly, we suddenly feel that everything around us is wildly familiar, that we've done it all before. This is déjà vu. There is an 'opposite' feeling, jamais vu, in which everything feels unfamiliar, even people one knows well. This is also sometimes seen in temporal lobe seizures.

Unfortunately for researchers, the brain's behaviour is never as simple as we think it is. Often, complex processes like learning rely on several different brain centres working together. As a result, seizures in different parts of the brain can produce confusingly similar symptoms. This makes it difficult to diagnose the epilepsy correctly, and also confounds our attempts to understand the brain's functions.

Also, seizures are rarely so obliging as to occupy a single well-defined area of the brain. They sprawl across several. The neuronal firing triggers neurones in neighbouring areas; travels rapidly down the brain's internal conduits. This means that distant brain centres are disrupted, causing symptoms with no apparent relation to the original seizure site.

And yet, the study of epilepsy can still teach us a great deal. With the advent of new imaging techniques, enabling us to 'see' activation spreading through the brain, the way is opening for a deeper understanding of the complex neural interactions that make us who we are.