Epilepsy is a disorder of the brain. In simple terms, our nervous system is a communications network that controls every thought, emotion, impression, memory, and movement, essentially defining who we are. Nerves throughout the body function like telephone lines, enabling the brain to communicate with every part of the body via electrical signals. In epilepsy, the brain's electrical rhythms have a tendency to become imbalanced, resulting in seizures.
The diagram below illustrates the outer surface of the upper brain. It contains numerous folds that increase the surface area and allow more cerebral cortex to be packed into the skull, giving us more "brain power."
The brain works on electricity. Normally, the brain continuously generates tiny electrical impulses in an orderly pattern. These impulses travel along the network of nerve cells, called neurons, in the brain and throughout the whole body via chemical messengers called neurotransmitters. A seizure occurs when the brain's nerve cells misfire and generate a sudden, uncontrolled surge of electrical activity in the brain.
Different areas of the brain control different functions. If seizures arise from a specific area of the brain, then the initial symptoms of the seizure often reflect the functions of that area. The right half of the brain controls the left side of the body, and the left half of the brain controls the right side of the body. So if a seizure starts from the right side of the brain, in the area that controls movement in the thumb, then the seizure may begin with jerking of the left thumb or hand.