Seizures are uncontrolled electrical activity in the brain, which may produce a physical convulsion, minor physical signs, thought disturbances, or a combination of symptoms.

The brain is an impressively wired computer. It stores information from input through our five senses and sifts through the data; gets rid of frivolous material and organizes the important stuff into short-term memory centers; and finally rearranges the final product into long-term memory. The brain also sends messages out electrically to the rest of the body, controlling movement and position so that the body can take the brain where it wants to go. Electricity is the key to its function, and sometimes it short circuits.

Seizures occur when parts of the brain becomes irritable and develop electrical surge. That surge can remain in a small area or it can spread to the whole brain. Normally, when we lift an arm, it is because part of the brain sends an electrical message through the spinal cord for the arm to move. The classic shaking of a seizure is witnessed when the whole brain fires, and the whole body moves. Usually the shaking is short-lived, because the brain doesn't like being irritated and it shuts itself down.

Every person has the potential to have a seizure. Usually the seizure threshold is high, and there needs to be an outside noxious stimulus to cause an electrical surge that is greater than that threshold for a seizure to occur. Seizures are often seen after head injuries - high fevers in children can also precipitate a seizure. In some people, the seizure threshold is set lower, and they may need medication to raise that threshold to prevent seizures.

After the seizure, it takes time for the brain to reboot, just like you computer. When it reboots, you can type as much as you want, but until the programs are ready to go, nothing is going to happen on the screen. Similarly, the brain needs time to reset itself and this post-ictal phase (the time immediately after a seizure) shows up as a period of confusion, sleepiness, or irritability.

The type of symptoms and seizures depend on where the abnormal electrical activity takes place in the brain, what its cause is, and such factors as the patient's age and general state of health.

Seizures can be caused by head injuries, brain tumors, lead poisoning, maldevelopment of the brain, genetic and infectious illnesses, and fevers. In fully half of the patients with seizures, no cause can yet be found.

See also epilepsy.