Figure 1. Causes of epilepsy by age of onset. Note that congenital causes predominate in the young, with cerebrovascular and degenerative diseases becoming important in the old. Also note that, in all age groups, a large number of cases are due to unknown causes. From: Hauser WA, Annegers JF and Kurland LT (1993) Incidence of epilepsy and unprovoked seizures in Rochester, Minnesota: 1935–1984. Epilepsia 34(3): 453–468.

Figure 2. Typical EEG in absence seizure. Top: Placement of electrodes on the scalp and relationship with underlying brain. Each line of the EEG compares electrical activity in a given electrode to a reference (in this case, the average voltage in 12 electrodes) over time. Bottom: The left side of the EEG tracing shows normal brain electrical activity, consisting of a fairly chaotic mix of waveforms. At the left arrow, brain activity suddenly becomes synchronized, at a frequency of three per second. Note that this is seen in all electrodes. At the right arrow, the seizure stops and normal brain activity resumes.

Figure 3. Abnormal EEG in a patient with partial seizures. Top: Placement of electrodes on the scalp and relationship with underlying brain. Each line of the EEG compares electrical activity in a given electrode to a reference (in this case, a central electrode called Cz) over time. Bottom: A sudden sharp wave interrupts normal sleeping brain activity (arrow). This is greatest at T3 (middle left temporal lobe), and is a marker for epilepsy. A smaller, similar, sharp wave is seen to the left.

Figure 4. EEG in a patient during a partial seizure. Top: Placement of electrodes on the scalp and relationship with underlying brain. Each line of the EEG compares electrical activity in a given electrode to a reference (in this case, a central electrode called Cz) over time. Bottom: Normal awake brain activity is interrupted by sudden, repetitive, rhythmic activity seen on the left (arrow), maximal at T5 (posterior temporal lobe). The discharge suddenly stops after 40 s with return of normal activity (right arrow).

Figure 5. Brain of a 33-year-old woman with intractable seizures, consisting of left arm contractions, as seen during epilepsy surgery. A grid of electrodes for recording seizures is in place. Red squares: central sulcus (separates frontal lobe from parietal lobe). Red circles: sylvian fissure (separates frontal lobe from temporal lobe). Blue squares: left-hand motor area. Green Xs: left-hand sensory area. Seizure activity was seen where blue circles and blue crosses are marked. Courtesy of Robert R. Goodman.