Understanding Epileptic Circuits

This article summarizes epileptic circuits and their role in seizure activity and spread.

• The brain stores memories and communicates with the rest of the body using specialized cells called neurons.
• These neurons are organized into circuits that perform a precise function when activated.
• Seizures can occur when several circuits activate at the same time.

Circuit Classification

Scientists have classified the different circuits involved in seizures based on their specific roles:

• Seizures start in sites called focus areas of the brain. When identified accurately, these are frequently the targets for epilepsy surgery since seizures cannot start without them. Depending on the type of epilepsy, there could more than one focus area. Decisions regarding surgery as a treatment option depend on the number of focus areas and their importance for a critical brain function, such as language or movement of one part of the body.
• Outside the focus areas, separate sets of neurons called initiating circuits are essential for a seizure to occur. These circuits connect the focus areas with other vital parts of the brain, forming a larger network to support and sustain the seizure’s activity.
• The seizure can then spread to different areas of the brain by recruiting secondary circuits in the pathways of spread. Not a lot is known about how this spread occurs. It is generally understood that this process causes widespread symptoms of epilepsy. This spread is responsible for causing a focal seizure to evolve into a generalized seizure. Studies on epileptic animal models suggest the pathway of spread involves interactions of the secondary circuits with both the seizure focus areas and the initiating circuits.
• All three of these components — the focus areas, the initiating circuits, and the pathway of spread — can be regulated by modulatory centers. These centers act as the brain’s checkpoints for damage control. Their functions may affect the severity of a seizure and the likelihood of its occurrence and spread. Recent animal model studies have shown that these modulatory regions are affected in epilepsy. As we increase our understanding of both the pathway of spread and the modulatory centers, we can design more therapies to reduce the spread and minimize the effects of a seizure.

Learn More

• More Basic Science of Epilepsy
• What happens during a seizure?