Each electrode is put either 10 or 20 per cent of the total distance between specific points on the head, done by measuring the person’s head and marking the position with a soft pencil. To work out where to put the electrodes, a special arrangement called the 10-20 system is used. When the technician or doctor is looking at the results of the EEG, they can tell what brain activity is happening, and in which particular part of the brain it is happening in. These electrodes are put in specific positions on the person’s head, which means that different electrodes can record the activity from different and known areas of the brain. When someone has an EEG, a number of electrodes are used (usually 25-30). Neurones control all of the body’s functions by communicating using electrical signals. The brain is made up of millions of neurones. Neurones – the scientific name for nerve cells. The activity is recorded on an electroencephalograph (recording machine) either on paper or more usually on computer. The EEG cannot interpret what the messages are ‘saying’ (or what you are thinking!), only that brain activity is happening.īecause the electrical signals are still quite small, they are amplified (made stronger) so that they can be recorded. The EEG shows brain function, and looks for the presence or absence of specific brain activity in specific areas of the brain. Instead, they record the electrical activity from small areas of the brain. The electrodes cannot pick up the electrical signals from individual neurones – the cells are far too small and the electrical charge is also too small. The electrodes only record the electrical activity of the brain they do not give out electricity. The electrical signals from the brain are picked up by small electrodes (about one centimetre across), which are placed on the person’s head. It is this electrical activity, sometimes called ‘brain waves’, that is picked up on by EEG. So when the brain is ‘working’ cells communicate using electrical signals, and when they do this they ‘give off’ electricity. These messages, called action potentials, happen due to changes in the electrical charge of the cells. ‘Brain waves’ and electrical signalsīrain cells (neurones) work by sending nerve impulses from one cell to another to transfer messages around the brain and the body. It does not look at the structure of the brain (how the brain is made up). An EEG looks at what is happening in the brain – the activity of the brain cells. The fact that epileptic seizures always start in the brain is important when considering the EEG. The difference between epileptic seizures and other seizures is that epileptic seizures are caused by a disruption in the way the brain is working. There are other medical conditions that might cause someone to have a seizure for example, diabetes.
But these tests, alongside other information, might help the specialist to decide if epilepsy is a likely cause of the seizures. Two of these tests are the electroencephalogram (EEG) and MRI.īefore we look at EEG in detail, we need to understand that neither of the tests will say for certain whether the person has epilepsy or not.
When someone has had seizures, and it is thought that they might have epilepsy, there are various tests that their specialist might ask for.
Sudden Unexpected Death in Epilepsy (SUDEP).