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Gelastic Epilepsy

Gelastic epilepsy is a type of epilepsy characterized by inappropriate laughter known as laughing seizures, though people with gelastic epilepsy may also experience other seizure types. Gelastic comes from the Greek word gelos, which means "laughter."


A gene is a unit of DNA that codes for the formation of a specific protein. Genes are the fundamental units of heredity. Genes come in pairs: One half of each pair is inherited from our mother, and the other half from our father.

Gene Mutation

A gene mutation is a permanent change in the DNA of a gene. Mutations can be inherited or can occur spontaneously.

Generalized Epilepsy with Febrile Seizures Plus (GEFS+)

Generalized epilepsy with febrile seizures plus (GEFS+) is a type of epilepsy caused by the mutation of a single gene. GEFS+ arises in childhood, with seizures occurring during episodes of fever, and then progresses to generalized seizures.

Generalized Seizures

Generalized seizures are thought to involve both sides of the brain spontaneously at seizure onset. Specialists recognize two classes of generalized seizures based on how they manifest themselves. Nonconvulsive generalized seizures alter consciousness but do not cause convulsions; convulsive generalized seizures also alter consciousness and cause repetitive jerking and stiffening movements. Generalized epilepsy is when a person has more than one generalized seizure.


Gestation is the period of time from the fertilization of the egg by the sperm until the birth of a child, or the length of a pregnancy.

Glial Cell

A glial cell is a specialized cell that surrounds nerve cells and provides structural and metabolic support. It is estimated that glial cells outnumber neurons by as much as 50 to 1. Also known as neuroglia or glia.

Glycemic Index

The glycemic index is a measure of a particular food's effect on the body's blood-sugar level. Foods that contain simple sugars, such as sucrose (table sugar), have a high glycemic index because they rapidly raise blood sugar after consumption. Conversely, many grains and legumes have a low glycemic index because they affect blood-sugar levels more slowly.

Grand Mal Seizure

See Tonic-Clonic Seizure.


Hemiparesis is a weakness or partial paralysis of one side of the body.


Hemiplegia is paralysis on one side of the body.


A hemispherectomy is a surgical procedure in which half of the brain, or one hemisphere, is removed. Hemispherectomy is used most often to treat intractable epilepsy where the epileptogenic region involves most of one cerebral hemisphere, such as in Sturge-Weber syndrome.


The hippocampus is a structure of the brain located in the mesial, or middle, of the temporal lobe. As part of the brain's limbic system, the hippocampus is important for learning and memory. The hippocampus functions in transferring information, including sensory inputs like tastes and sounds, into memory. The hippocampus, along with the amygdala, also functions in integrating and recalling spatial memory, as well as processing and controlling emotion.


Hydrocephalus is a buildup of cerebrospinal fluid in the ventricles of the brain, causing increased intracranial pressure. Hydrocephalus may present at birth or result from a head injury or tumor, and can cause seizures.


Hyperventilation is increased rapid and deep breathing. Hyperventilation is often used as an activating procedure during an EEG because it can sometimes provoke abnormal brain wave activity, helping doctors make a diagnosis or identify an individual's seizure type.


Hypoxia is a condition in which there is a deficiency or inadequate amounts of oxygen reaching the tissues. An insufficient supply of oxygen to the brain can cause seizures.


Hypsarrhythmia is a markedly abnormal and chaotic EEG pattern characterized by multifocal spike and slow wave discharges, very high amplitudes, and lack of organization. Hypsarrhythmia is a characteristic of West syndrome.


Ictal refers to the period of time during a seizure.


The word ictus comes from Latin and means "sudden attack." In epilepsy, an ictus is a seizure.


The word idiopathic refers to a disorder or symptom of unknown cause, as in idiopathic epilepsy or idiopathic seizures. Approximately 65 to 70 percent of epilepsy cases are idiopathic.

Individualized Educational Plan (IEP)

An Individualized Education Plan (IEP) is a written education plan for a student with learning disabilities that is developed by a team of professionals (teachers, therapists, etc.) and the student's parents. An IEP is based on a multidisciplinary evaluation of the student, describing how the student is currently doing, what the student's learning needs are, and what services will be needed to optimize the student's learning potential.

Infantile Spasms

Infantile spasms is an epilepsy syndrome that affects infants and very young children. The syndrome is characterized by a form of myoclonic seizures, which may be identified by a sudden jerking of the body, in which the child flexes or extends at the trunk. The indication may also be more subtle, such as staring or blinking. Infantile spasms commonly appear in clusters, typically occurring as the child is going to sleep or soon after waking.

Although not all spasms are immediately obvious, parents are still likely to pick up on the subtle clues that suggest something may be out of the ordinary with their child. Acting quickly on these suspicions by seeking the advice of a pediatrician or epilepsy specialist is critical to controlling infantile spasms. Appropriate treatment may in turn reduce the incidence and severity of learning disabilities and behavioral disorders associated with these seizures. See also West Syndrome.


Inhibition refers to the processes through which brain electrical activity is slowed, causing nerve cells to stop firing. Healthy brain function relies on a balance of excitation and inhibition of nerve cells. Seizures are thought to occur when there is too much excitation or too little inhibition in the nerve cells of the brain.


Interictal refers to the period of time between seizures.


Intractable seizures are seizures that are difficult to control with anticonvulsant medications. If an individual's epilepsy is intractable, it typically means that two or more appropriate medications have failed to adequately control seizures. Also known as refractory.


An ion is an electrically charged atom or group of atoms. The atoms become electrically charged by gaining or losing one or more electrons. For example, sodium, potassium, and calcium all gain an electron and become positively charged, while chloride loses an electron and becomes negatively charged.

Ion Channels

Ion channels are the proteins that allow for and regulate the flow of ions across cell membranes.

Juvenile Myoclonic Epilepsy (JME)

Juvenile myoclonic epilepsy (JME) is an epilepsy syndrome that typically begins in late childhood or early adolescence. It is characterized by myoclonic jerks as the individual is going to sleep or waking, though typically in the morning. Children describe intense feelings of jumpiness that generally subside after about 30 minutes. In addition to the myoclonic seizures, children with juvenile myoclonic epilepsy also have periodic tonic-clonic seizures.

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This content was last reviewed on November 20, 2006.