Seizures can be categorized as either partial or generalized. A partial seizure is a sudden change in consciousness, muscle control or behavior caused by abnormal activity in an isolated part of the brain. In generalized seizures, the entire brain is affected.

It is often difficult to identify whether a seizure is partial or generalized. Roughly 60 percent of people with epilepsy (condition marked by recurrent seizures) experience partial seizures, according to the National Institute of Neurological Disorders and Stroke (NINDS). In addition, partial seizures can sometimes trigger generalized seizures if the initially localized abnormal activity spreads to other parts of the brain.

Seizures involve a sudden increase in electrical activity in the brain. Neurons (nerve cells) normally produce electrochemical signals that instruct other parts of the body to perform certain actions, such as moving the body or feeling certain emotions or sensations.

A seizure occurs when something disturbs the pattern of electrochemical signaling and causes the neurons to fire at a much faster rate than normal. This storm of electrical activity in the brain can result in a seizure, possibly producing changes in mood or behavior, hallucinations, involuntary muscle contractions, loss of consciousness or involuntary movements. During a partial seizure, the symptoms that are experienced depend upon the area of the brain affected.

Partial seizures can be categorized as being either simple or complex. During a simple partial seizure, consciousness is not lost. However, it may be altered. People who have simple partial seizures may experience abnormal sensations such as inexplicable feelings of joy, anger or sadness. They may also see, hear, smell or taste things that are not really there (hallucinations).

During a complex partial seizure, people may experience a pronounced change in or loss of consciousness. They may appear to be “out of it” or in a dream-like state. They may also make repetitive movements that appear to be conscious (called automatisms), such as smacking the lips or picking at clothing.

Complex partial seizures may sometimes develop into a generalized seizure, most often a tonic-clonic seizure. When this occurs, it is sometimes called a partial onset seizure or secondary generalized seizure. In some cases, there is a clear difference between the initial partial seizure and the secondary generalized seizure. However, in other cases, the generalized seizure is triggered so fast that physicians may have difficulty identifying that an initial partial seizure preceded the generalized seizure.

Most partial seizures have no known cause. Some types of partial seizures are more likely to be caused by certain factors, such as head injuries or brain tumors. Under certain circumstances (e.g., electrical stimulation, high fever, exposure to certain drugs), anyone may experience a seizure. Having a single partial seizure, even one that is seemingly unprovoked, does not necessarily mean another seizure will occur. However, recurrent partial seizures, especially of the same type, may be an indication of a chronic underlying neurological condition.

Experiencing a partial seizure may be distressing. People who have a simple partial seizure are generally aware of changes that may occur (e.g., hallucinations), although they cannot control them. This may be especially worrisome for children with seizures, who often need reassurance from caregivers during and after the seizure. People who have a complex partial seizure are generally not aware of their actions during the seizure, although it may seem as if they are performing conscious tasks (e.g., chewing, swallowing, undressing themselves). This can sometimes be troublesome for the person having the seizure, whose actions may be misunderstood by onlookers.