Each hemisphere of the brain has four distinct sections, or lobes. These are the frontal, parietal, temporal and occipital lobes. These lobes in turn each have left and right sections, reflecting the division of the brain into left and right hemispheres. Damage to any of these eight structures can leave scarring or other sensitive areas capable of producing seizures. The nature of the seizures varies, however, since the lobes control different behaviors, movements and experiences. For example:
- In most right-handed people, the left frontal lobe (behind the forehead) controls speech while the left temporal lobe (above the ear) controls understanding of spoken and written language.
- The occipital lobes, at the back of the head, control vision. Neuronal discharge in the occipital lobes could make objects appear larger or smaller than they are, or produce distorted visual images.
- The left and right parietal lobes each control muscles of the leg, hip, trunk, arm, hand, face, tongue and vocal chords on the (opposite) right and left sides of the body. A seizure that affects this part of the brain might produce just the twitch of a hand or facial muscles, or might progress to involve the whole of one side of the body.
- The left temporal lobe incorporates hearing, language, and verbal memory.
- The right temporal lobe also includes hearing, plus musical appreciation.
- The limbic cortex (incorporating deep, central portions of the frontal and temporal lobes) controls emotions and memory. This area is frequently the site where partial seizures begin.
- The hippocampus, an area of the brain just below the temporal lobes, plays a key role in memory, especially recent memory.