What does the EEG tell the doctor?
　　　　　　　　　　

　　　The EEG (electroencephalogram) displays the electrical activity of the brain. Nerve cells in the brain are constantly creating very small electrical signals, whether a patient is waking or sleeping. The EEG machine contains amplifiers which make these signals, or brainwaves, big enough so we can see them.
　　　　　　
　　　　　
How can the EEG help in the diagnosis and treatment of seizures?
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　　　The EEG is still the most important test used to help diagnose seizures and epilepsies. Many people do not have a detectable brain lesion causing their seizures, and tests like the MRI and CT scan show no abnormal finding of the brain structure. The EEG, however, can show abnormal electrical signals of the brain even when these other tests are no abnormal findings.
　　　
　　　The EEG of persons with epilepsy can be divided into two categories, the interictal and ictal EEG. The interictal EEG is the EEG recording taken when the patient is not having seizures. Most patients with seizures will have at least one interictal EEG. This test is done to look for interictal epiliptiform abnormalities, that is, abnormal activity that can occur in a patient with epilepsy in the absence of an actual seizure. Sometimes the patient is asked to attempt to go to sleep, or to hyperventilate, or a strobe light is flashed in his or her eyes to try to bring out these abnormalities. Finding these abnormalities prove that the patient has epileptic seizures, and helps the doctor determine what type they are. The ictal EEG is the EEG recording taken during an aura and/or a seizure. This is done when a patient's seizures fail to respond to treatment, and the doctor wants to confirm the diagnosis, or possibly determine if brain surgery can be used to treat the seizures. Usually, ictal EEG recordings need to be made during closed-circuit television monitoring ( video-EEG) in an Epilepsy Center. For these tests, the person is usually admitted to the hospital and has their EEG and their video recorded continuously to capture actual seizure events.
　　　　
　　　　　　
What does the EEG tell the doctor? 　　< back top >
　　　
　　　The most common interictal EEG abnormality in persons with epilepsy is a spike, which is a burst of electrical activity that stands out from the normal EEG patterns. These spikes can be confined to one area of the brain (focal), or can occur in several areas of the brain independently of each other (multifocal), or come simultaneously from wide areas of the brain (generalized). The pattern of interictal abnormalities can determine if the person has focal or generalized epilepsy. These types of epilepsy have different causes, and may respond to different drugs.
The ictal EEG abnormalities are a little more complicated. These abnormalities can show rhythmic activity but can also show other EEG patterns depending on whether the recording was done from scalp electrodes or from electrodes placed on the brain surface or in the brain. The ictal EEG of the person with generalized epilepsy will usually show widespread brain involvement from the onset of the seizure. The ictal EEG of the person with focal epilepsy will usually show the seizure starting from a specific brain area but it can then spread to involve other areas, or even the whole brain. These patterns can tell the doctor which part of the brain is causing the seizure and how much of the brain becomes involved during it.
　　　　
　　　In summary, the EEG is the most important test used in the diagnosis and treatment of epilepsy because it shows abnormal brain signals even if the brain structure is normal. The EEG records the electrical activity of the brain between seizures, and during seizures. By looking at the patterns of the EEG in these different stages the doctor can tell if the patient has seizures, which type of epilepsy the person has, and which part of the brain is causing the seizures. This information can help the doctor to determine which medication is appropriate to treat the seizures. If medications do not help, and a specific area was found to cause the seizures, then the person may be eligible for neurosurgical treatment.