About 50 million people have epilepsy worldwide, but for decades, the causes and effects of epileptic seizures were a frightening mystery. As scientists began to unlock the secrets of the brain, terminology for seizures changed over time. In 2017, the International League Against Epilepsy released its newest classifications of epileptic seizure types. These divide epileptic seizures into categories based on how much of the brain they affect, how they alter a person’s awareness, and whether they produce motor or nonmotor symptoms.
All epileptic seizures occur when the brain’s electrical signals misfire, but the effects differ depending upon which parts of the brain are affected. There are two main types of epileptic seizure: generalized and focal. Focal seizures (previously called “partial seizures”) start in a specific area or network of cells on one side, or hemisphere, of the brain. Approximately 60 percent of people who have epilepsy experience focal seizures.
Focal seizures are categorized by the different levels of awareness people experience while having one. Seizures cause a range of cognitive effects. Some seizures appear to be a quick moment of daydreaming or are unnoticeable to an outside observer, while others involve full loss of consciousness.
Someone having a focal aware seizure (previously called a “simple partial seizure”) is fully awake and alert while the seizure is happening. About 14 percent of people with epilepsy experience focal aware seizures. A person having a focal aware seizure might freeze up and be unable to respond to others while it is happening. This halt in speech and movement is called behavioral arrest. However, some people are fully able to interact with others while the focal aware seizure is occurring. Once the seizure is over, the person will remember events that happened during the seizure. Focal aware seizures are short, usually lasting two minutes or less.
About 36 percent of people with epilepsy have focal impaired awareness seizures. A person having a focal impaired awareness seizure (previously called a “complex partial seizure”) does lose awareness of their surroundings. The person often has a blank stare or may be unable to respond to others. Many people experiencing a focal impaired awareness seizure make automatic movements that seem to be purposeless, called automatisms. Moving one’s mouth with chewing movements or lip smacking is common, as is picking at clothes. Some people will walk aimlessly, which can be dangerous. Others may try to take off their clothes, respond aggressively to intervention, scream, or cry. Focal impaired awareness seizures usually last for one or two minutes. When the focal impaired awareness seizure is over, the person might not remember that it happened, and they will probably feel tired for a few hours.
Some seizures are categorized as awareness unknown, as the seizure occurs when there is no witness. In some cases, even an electroencephalogram (or EEG, a diagnostic test that measures electrical activity in the brain) cannot determine what type of seizure has occurred. A routine EEG may be normal, but an EEG placed while the person is actively seizing will offer more information. Having a normal EEG between seizures does not rule out the possibility of seizures occurring at other times or a diagnosis of epilepsy.
After a focal seizure is categorized as aware or impaired awareness, it is subcategorized as either a motor or a nonmotor seizure.
Focal motor seizures affect the muscles. Because focal seizures affect only a part of the brain, focal motor seizures usually affect a specific body part, not the entire body, as with a generalized seizure. There are several subtypes of focal motor seizure.
During a tonic focal motor seizure, the muscles tense up, often affecting the head, arms, or legs. These seizures are short, lasting about 20 seconds. During an atonic focal motor seizure, or drop seizure, the muscles go limp. A person experiencing this type of seizure may fall down or drop something they are holding. Their head might fall forwards, or they might involuntarily close their eyes. Like tonic seizures, atonic seizures are short, lasting about 15 seconds. Both tonic and atonic focal motor seizures can cause a standing person to fall to the ground.
Myoclonic focal motor seizures cause the muscles to stiffen and relax very quickly, in movements shorter than a second, causing a jerking motion. (Even people who do not experience seizures do experience myoclonic muscle movements when they hiccup.) Myoclonic focal motor seizures are usually also focal aware seizures, with the person retaining consciousness throughout.
Hyperkinetic focal motor seizures affect the arms and legs, and the muscles that control the head, spine, and jaw. A person experiencing a hyperkinetic seizure makes large, involuntary movements, such as thrashing, jumping, rocking, pedaling at the air, or thrusting the pelvis.
It is important to note that not every focal seizure causes involuntary muscle movement. Focal nonmotor seizures involve changes in thinking, emotions, or sensation.
Read more about the additional subtypes of focal motor seizures.
Some seizures affect thought, language, and understanding. These are known as cognitive seizures. While undergoing a cognitive seizure, a person might be unable to speak or to understand language. During a cognitive seizure, a person also might not recognize the meaning of sounds. For example, a person might hear a phone’s ring tone, but not understand that it means someone is calling.
Emotional seizures are similar to cognitive seizures. A person experiencing an emotional seizure has an emotional response that is inappropriate to the situation. The person may not actually feel the emotion, but simply go through the activities associated with the emotion, such as uncontrolled laughing (gelastic seizure) or crying (dacrystic seizure). Sudden feelings of fear or panic are common during emotional seizures. In rare cases, emotional seizures can cause extreme anger or joy.
Seizures that affect hearing, smell, taste, vision, and touch are known as sensory seizures. Symptoms of a sensory seizure include visual and aural hallucinations, tasting and smelling things that are not there, and sensations such as “pins and needles” tingling and numbness. A person experiencing a sensory seizure might also feel dizzy.
Autonomic seizures affect involuntary functions, such as the gastrointestinal and cardiovascular systems. During an autonomic seizure, a person might belch, experience flatulence, or vomit. This is sometimes called abdominal epilepsy. Other autonomic seizure symptoms include changes in heart rate, changes in breathing, and involuntary urination. Some people experience sexual arousal.
Behavior arrest seizures display a decrease or stop in ongoing motor activity. Sometimes, the person will “freeze” entirely, stop talking, or stop or decrease movement. Because this is frequent in seizure disorders and sometimes difficult to notice at the beginning of a seizure, the behavior arrest in this type of seizure must be prominent and persist throughout the totality of the seizure. Behavior arrest can be seen in both focal aware and focal impaired awareness seizures.
Different types of focal seizures — whether aware or impaired awareness, motor or nonmotor — originate in different regions of the brain. The specific symptoms of focal seizures are heavily influenced by the region of the brain in which they originate.
The temporal lobes of the brain, which sit above the ears, help process vision, language, and emotions. Disturbances in the temporal lobes are the most common cause of focal impaired awareness seizures. Between 40 percent and 80 percent of people who have seizures of temporal lobe origin experience automatisms, such as chewing or picking at clothes. Other symptoms of temporal lobe seizures include vomiting, speech, and urination. Temporal lobe seizures tend to provoke confusion.
The brain’s frontal lobes are located directly behind the forehead. They are associated with higher-level executive functions, such as focus, problem-solving, and voluntary movement. Thirty percent of people who have focal seizures experience seizures originating in the frontal lobes. Hyperkinetic seizures commonly start there. Seizures that originate in the frontal lobes tend to be shorter (about 30 seconds), but occur frequently throughout the day and at night during sleep. People recovering from a frontal lobe seizure tend to have less confusion and drowsiness than those recovering from a temporal lobe seizure.
The brain’s parietal lobes are at the top and center of the head. They monitor the sense of touch and our sense of position (knowing where our limbs are, for example). Seizures focused in the parietal lobes tend to cause vertigo (sensation of the room spinning) or visual symptoms, such as hallucinations. They can also cause emotional reactions, such as panic attacks, and behavioral arrest.
The occipital lobes are at the back of the head. They process color and motion. Focal seizures in the occipital lobes can cause blinking and visual hallucinations, such as complete visual whiteout or blackout. These symptoms can be similar to those of migraine auras, although they are usually shorter than those associated with migraines (two minutes as opposed to five to 15 minutes).
While seizure symptoms can suggest the probable origin of an epileptic seizure, the exact origin of a seizure must be found through an EEG diagnostic test.
Wherever focal seizures originate, there is a question about their underlying cause. There are many potential causes of epileptic seizures. Traumatic brain injury, stroke, brain tumors, and infection are the main known causes of epilepsy. Some people develop epilepsy from genetic or chromosomal abnormalities, metabolic disorders, or prenatal birth injury. Infection, especially in developing countries, is the most common discovered cause of epilepsy. These infections include meningitis, viral encephalitis, HIV, tuberculosis, malaria, and neurocysticercosis.
For about half of people with epilepsy, a definitive underlying cause is never found for their seizures.
Some people with epilepsy experience auras before a seizure. These auras can involve déjà vu (a feeling of reliving an experience), tasting or smelling something that is not there, muscle twitching, numbness, or visual disturbances such as seeing lights or a hallucination.
These auras are actually seizures in and of themselves — focal aware seizures. They do not seem like seizures because they precede more severe episodes called tonic-clonic seizures. (Tonic-clonic seizures were formerly called “grand mal” seizures, while absence seizures were referred to as “petit mal” seizures.) After the focal seizure occurs, the electrical activity spreads throughout the brain, causing a generalized seizure. These tonic-clonic seizures involve muscle stiffening, loss of consciousness, and convulsions, so it is no surprise that the preceding focal seizure is not often recognized as anything more than a warning of the symptoms to come.
Different treatments may be used to control seizures of different types. Learn more about treatment options for focal seizures.