Absence seizure (also known by the older term "petit mal seizure"): a seizure that causes a brief loss of awareness. The patient stops any activity and stares blankly. Occasionally, there might be some blinking.

Anatomic hemispherectomy: a surgical procedure during which an entire hemisphere of the brain, including the corpus callosum, is removed.

Anticonvulsant: an antiepileptic drug used to control both convulsive and non-convulsive seizures.

Atonic seizure: a seizure that causes a sudden loss of muscle tone, particularly in the arms and legs, and often causes the patient to fall.

Aura: a warning or initial symptom at the beginning of a seizure, experienced by the patient, but not visible to observers. (Auras might progress to become focal or even generalized seizures, or they might exist alone.) Not all patients experience auras.

Clonic seizure: a seizure with repetitive, rhythmic jerks that involve all or part of the body.

Complex partial seizure: a seizure that includes loss of awareness; for example, patients seem to be "out of it" or "staring into space." Other movements may occur as part of the seizure.

Corpus callosum: a band of nerve fibers located deep in the brain that connects the two halves (hemispheres) of the brain. (The corpus callosum helps the hemispheres share information.)

Corpus callosotomy: an operation that cuts the corpus callosum and interrupts the spread of seizures from one hemisphere of the brain to the other. (Callosotomies might be complete or might involve only a portion of the corpus callosum. Although seizures generally do not completely stop after this procedure, they usually become less severe.)

EEG-video monitoring: continuous simultaneous recording of brainwaves and video observation of the behavior accompanying the EEG. (This technique, carried out at comprehensive epilepsy centers, is used to diagnose epilepsy and localize the seizure focus. The results are useful to determine therapy, medical or surgical.)

Electrode: a conductive disk (usually metal) attached to the scalp that conveys the electrical activity of the brain through a wire to an EEG machine. (Typically, 21 electrodes are temporarily pasted to the scalp during an electroencephalogram.)

Electroencephalogram (EEG): a diagnostic test that measures brainwaves, the electrical impulses in the cerebral cortex. (This test helps a physician to diagnose epilepsy.)

Epilepsy: a chronic medical condition marked by recurrent epileptic seizures. (Patients might have single seizures as a result of fever, medicine withdrawal, etc., but are not labeled as having epilepsy if seizures do not recur.)

Epileptogenic zone: the region of the brain responsible for the abnormal electrical signals that cause seizures.

Epilepsy surgery: a neurosurgical procedure to prevent further seizures, usually accomplished by removing the epileptogenic zone. (This is successful in eliminating seizures in a large majority of patients, depending on the type of epilepsy identified during EEG-video monitoring.)

Functional hemispherectomy: a procedure during which portions of one hemisphere of the brain that is not functioning normally are removed, and the corpus callosum is split. (This interrupts the communication among the various lobes and between the two hemispheres and prevents the spread of seizures.)

Generalized seizure: a seizure that occurs throughout the brain.

Grand-mal seizure: an older term for a seizure during which the patient loses consciousness and collapses. (The patient also has body stiffening and violent jerking, and may go into a deep sleep or become confused. This seizure is also known as a generalized convulsion.)

Hemisphere: one half of the brain

Ketogenic diet: a treatment for epilepsy intended to maintain fasting metabolism for a long period in order to create ketones, byproducts of fat-burning metabolism. (Seizures often lessen or disappear during periods of fasting. The diet is very high in fat and low in carbohydrates. The diet is most often recommended for children ages 2 through 12 who have been diagnosed with a generalized type of epilepsy and who have failed to respond to a variety of medicines.)

Lesionectomy: surgery to remove isolated brain lesions that are responsible for seizure activity.

Lobe: one of the sections of the cerebrum, the largest part of the brain (The lobes are divided into four paired sections — frontal, parietal, occipital, and temporal. The seizure focus may be located in one of the lobes.)

Lumbar puncture: a diagnostic procedure during which the fluid surrounding the spinal cord (cerebrospinal fluid) is withdrawn through a needle and examined in a laboratory. (The procedure is also known as a spinal tap.)

Multiple subpial transection: a surgical procedure to help control seizures that begin in areas of the brain that cannot be safely removed, areas that control movements or speech (The surgeon makes a series of shallow cuts [transections] in the brain tissue to interrupt the movement of seizure impulses.)

Myoclonic seizure: a seizure that consists of sporadic jerks, usually on both sides of the body. (Patients with these seizures might drop or involuntarily throw objects.)

Neurologist: a doctor who specializes in the treatment of disorders of the brain and nervous system (such as epilepsy).

Neuron: a single nerve cell. (The brain is made up of billions of neurons. Many neurons malfunctioning together are necessary to produce a seizure.)

Non-epileptic event: an event that resembles a seizure but is actually produced by another condition, such as Tourette’s syndrome and heart rhythm disturbances, called arrhythmias. (Certain psychological conditions can also bring on a non-epileptic event.)

Partial seizure: (also know as a "focal seizure") a seizure that occurs in a limited area in only one hemisphere of the brain. (This type of seizure is more amenable to treatment with surgery than are generalized seizures.)

Seizure: an event of altered brain function caused by abnormal or excessive electrical discharges in the brain. (Most seizures cause sudden changes in behavior or motor function.)

Seizure focus: the area of the brain where a seizure starts.

Status epilepticus: a prolonged seizure or a series of repeated seizures without regaining consciousness. (Status epilepticus is a medical emergency, and medical help should be obtained immediately.)

Temporal lobe resection: a surgical procedure during which brain tissue in the temporal lobe is cut away (resected) to remove the seizure focus.

Tonic seizure: a seizure that is characterized by stiffening of the muscles, sustained for more than a few seconds.

Tonic-clonic seizure: a seizure marked by loss of consciousness, falling, stiffening, and jerking. (This is the hallmark of a generalized motor seizure, which used to be called a "grand mal seizure.")

Vagus nerve stimulation: a surgical treatment for epilepsy involving implantation in the neck of an electrode on the vagus nerve. (The electrode is connected to a pacemaker that is placed under the skin in the chest. The VNS is programmed to cycle continuously. However, if the patient feels a seizure coming on, additional therapy can be given by placing a small magnet over the VNS.

Vagus nerve: a small nerve that passes through the neck and is connected to various areas of the brain.