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See Applied Behavioral Analysis.

Absence Seizure

An absence seizure (formerly known as a petit mal seizure) is a type of generalized seizure that typically occurs without warning and causes lapses of attention lasting from 5 to 30 seconds. Most children with absence seizures experience what physicians call typical absence seizures, which may involve eye blinking, head bobbing, or jerky movements of the face or lips, in addition to the characteristic lapses of attention. Atypical absence seizures are similar but involve a distinctive EEG pattern of slow spike and wave discharges. Atypical absence seizures are usually associated with Lennox-Gastaut syndrome. Absence seizures are often called staring seizures.




Acidosis is a condition in which there is an increased amount of acid in the blood, resulting in a drop in blood pH.

Activating Procedure

An activating procedure is a practice used during an EEG to provoke a clinical seizure or epileptiform discharge. Activating procedures include hyperventilation and photic stimulation, during which a strobe light is flashed at various frequencies while an individual opens and closes his or her eyes.


See Attention Deficit Hyperactivity Disorder.

Aicardi Syndrome

Aicardi syndrome is a very rare neurological disorder that affects only girls (doctors think Aicardi syndrome is lethal to male embryos in utero). The disorder is thought to be genetic, although the gene has yet to be identified. Aicardi syndrome is diagnosed based on the presence of three clinical features: coloboma, or absence of normal tissue in the retinas of the eyes; partial or complete absence of the corpus callosum in the brain; and a serious type of seizure called infantile spasms.


The amygdala 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 amydala functions in integrating the senses, including sight and hearing, as well as processing and controlling emotion. The amygdala, along with the hippocampus, also functions in transferring information into memory.

Angelman Syndrome (AS)

Angelman syndrome (AS) is a genetic disorder characterized by seizures, ataxia (unsteady gait), language problems (most individuals with AS are nonverbal), cognitive impairment (which is often severe), and a happy demeanor. Because of the way Angelman children walk and their generally joyful disposition, AS is often referred to as the "happy puppet" syndrome.

Anticonvulsant Medication

An anticonvulsant medication is a drug prescribed to help manage seizures by controlling excessive electrical activity in the brain. It is sometimes referred to as an antiepileptic drug (AED).

Applied Behavioral Analysis (ABA)

Applied behavioral analysis (ABA) is a therapeutic educational intervention that has been used successfully with children on the autism spectrum and children with other types of severe learning disorders. The method employs structure and repetition to modify behaviors and introduce new skills.

Atonic Seizure

An atonic seizure is an abnormal discharge of electrical activity in the brain that causes a sudden complete loss of muscle tone or posture. All large muscle groups relax, the limbs go limp, and the individual falls to the floor or ground in what experts generally refer to as a "drop attack."

Attention Deficit Hyperactivity Disorder (ADHD)

Attention deficit hyperactivity disorder (ADHD) is a neurobehavioral disorder that makes learning and social interactions difficult, even for those with normal cognitive abilities, by causing individuals to be easily distracted and frustrated, fidgety, impulsive, and forgetful.

Atypical Absence Seizure

See Absence Seizure.


An aura is a simple partial seizure, which serves as a warning sign occurring seconds or minutes before a complex partial seizure or a partial seizure with secondary generalization. An aura is typically an unusual physical sensation such as a smell, a sound, a feeling of fear, or a sick feeling in the stomach.


Autism is a spectrum disorder, or symptom complex, characterized by deficits in verbal and nonverbal communication skills, severe social dysfunction, and repetitive behaviors. Also known as autism spectrum disorder.


Automatisms are small, repetitive movements during a seizure. Automatisms are involuntary and may include, for example, movements of the mouth or limbs, blinking of the eyes associated with absence seizures, or picking at one's buttons. Automatisms occur most often with absence or complex partial seizures, or after tonic-clonic seizures. Because consciousness is lost, individuals are typically not aware that these movements have occurred.

Autonomic Nervous System

The autonomic nervous system is the part of the nervous system responsible for regulating the involuntary vital functions of the body, including digestion, breathing, heartbeat, and blood flow.

Autosomal Dominant Nocturnal Frontal Lobe Epilepsy

Autosomal dominant nocturnal frontal lobe epilepsy is caused by a single gene mutation in one of three genes. This type of epilepsy produces shaking movements mostly during sleep.


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Axons are the long nerve fibers through which nerve cells transmit signals.

Benign Epilepsy Syndromes

Seizures associated with benign syndromes are typically well controlled with medications, are not associated with other neurological symptoms such as learning disabilities, and are often outgrown.

Benign Familial Neonatal Convulsions

Benign familial neonatal convulsions is a type of epilepsy caused by the mutation of a single gene. It usually begins prior to the third day of life and typically goes into remission after two or three weeks.

Benign Rolandic Epilepsy (BRE)

Benign rolandic epilepsy (BRE) is an epilepsy syndrome that typically arises after three years of age and is considered benign because children usually outgrow it by adolescence. In most children with BRE, seizures are infrequent and sometimes do not require medication. Characteristic manifestations of the seizures associated with this syndrome begin with a sensation at the corner of the mouth and drooling, followed by jerking of the mouth that can progress to the rest of that side of the face, and sometimes to that entire side of the body. Although children remain conscious during this type of seizure, they usually are unable to speak for a period of time during and after the seizure. Seizures occur more commonly at night, especially during particular stages of sleep.



Brain Stem

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The brain stem is the lowest part of the brain. It connects the midbrain to the spinal cord. The brain stem is comprised of the pons located in the upper portion of the brain stem and the medulla oblongata located in the lower portion of the brain stem. The pons is a bundle of nerve fibers linking the left and right sides of the cerebellum. The medulla oblongata's main function is to relay nerve signals between the brain and the spinal cord. The medulla oblongata also functions to help control autonomic functions including breathing and heart contractions, as well as reflex activities such as swallowing and coughing.

Brain Mapping

See Electrocorticography.

Catastrophic Epilepsy Syndrome

Seizures associated with catastrophic syndromes are often refractory to treatment and are often associated with developmental sequelae.


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The cerebellum is the part of the brain located at the back of the head, below the cerebrum and behind the brain stem. The cerebellum is responsible for coordination and balance.

Cerebral Cortex

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The cerebral cortex is the highly folded, neuron-rich outer layer of the cerebrum that is referred to as gray matter.


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The cerebrum is the largest and most recognizable of the brain's structures. It is made up of a highly folded outer layer, called the cerebral cortex, and an inner layer rich in nerve fibers, which carry signals from the cortex to targets in other parts of the body. The cerebrum is divided into right and left hemispheres, with a bundle of fibers called the corpus callosum connecting and aiding in communication between the two halves. Each hemisphere can be divided further into four functionally distinct lobes: frontal, parietal, occipital, and temporal.

Childhood Absence Epilepsy (CAE)

Childhood absence epilepsy (CAE) is an epilepsy syndrome characterized by absence seizures that occur from one to dozens—and sometimes hundreds—of times per day. Seizures typically arise during childhood between the ages of four and eight years. Tonic-clonic seizures may precede absence seizures and may recur periodically after absence seizures have begun. Most children with childhood absence epilepsy outgrow the propensity for seizures by adolescence. Because of this, CAE is considered a benign epilepsy syndrome.


Chromosomes are structures located in the nucleus of a cell that contain our genetic material (genes). Humans have 23 pairs of chromosomes: Half of each pair is inherited from our mother, and the other half from our father.


The term cognitive refers to the collective mental processes through which knowledge is acquired. It involves, among other things, perception, memory, reasoning, and intuition.

Complex Partial Seizures

Complex partial seizures begin in one area, or focus, of the brain, and then progress, or spread, to other areas of the brain, where they affect consciousness or cause staring, confusion, or loss of alertness. In some cases, they also cause aimless movements called automatisms, such as lip smacking or picking at clothes, the repetition of words or phrases, or inappropriate laughter. See also Partial Seizure.

Computed Tomography (CT)

Computed tomography (CT) is a procedure that uses x-rays and computer technology to produce cross-sectional images of the internal structures of the body, including the brain. The images produced are more detailed than traditional x-ray images. Also known as a CAT scan.


Consciousness is the state of being aware. If consciousness is preserved during a seizure, the individual is aware that the seizure is happening and can respond. If consciousness is lost during a seizure, the individual may appear unresponsive for a short period of time and may not remember the seizure.

Corpus Callosotomy

A corpus callosotomy is a surgical procedure to sever the corpus callosum, the thick band of nerve fibers connecting the right and left sides of the brain. The procedure is done to stop the spread of seizures from one hemisphere to the other.

Corpus Callosum

brain sectionsclick to enlarge photograph

The corpus callosum is the thick band of nerve fibers connecting the right and left sides of the brain.

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This content was last reviewed on November 20, 2006.