Seizure Mechanisms and Threshold

A seizure is a massive disruption of electrical communication between neurons in the brain, leading to the temporary release of excessive energy in a synchronized form. Neurons communicate with each other by firing electrical impulses. These impulses travel from the neuron along the axon, and then stimulate the release of neurotransmitters which flow across the synaptic cleft (the gap between the cells) to the dendrites of the receiving cell.

If more excitatory than inhibitory transmitters are released, the cell will fire; if more inhibitory neurotransmitters are released, the cell will not fire. Since large numbers of cells are involved in even simple actions, the on/off action serves to control physical and mental functioning.

However, if there is a consistently higher level of the excitory neurotransmitters, or too few inhibitory ones, the likelihood of a seizure—an uncontrolled, continuing firing of neurons in the brain—is increased. Some of the newer medications relate directly to this process and are designed to increase the level of inhibitory neurotransmitters, especially gamma-aminobutyric acid (GABA), or to decrease the amount of the excitatory ones, such as glutamate.

A sudden burst of neuronal firing may not be sufficient to cause an obvious seizure (although it might show up as a sudden spike on the EEG); however, if the discharge of electrical energy has sufficient power and affects enough neurons, it will produce symptoms characteristic of the area in which the discharge took place. The result could be a sudden muscle jerk, an abrupt fall, a distorted vision. If the disturbance flashes across the whole brain at once, it could produce a convulsive seizure, temporarily disrupting many of the functions of the brain.

Seizure Threshold

This concept holds that everyone has a certain balance (probably genetically determined) between excitatory and inhibitory forces in the brain. The relative proportions of each determine whether a person has a low threshold for seizures (because of the higher excitatory balance) or a high threshold (because of greater inhibition). According to this view, a low seizure threshold makes it easier for epilepsy to develop, and easier for someone to experience a single seizure.