Basic Mechanisms Underlying Seizures and Epilepsy
This page contains a brief overview of the basic mechanisms underlying seizures and epilepsy and is intended for a general audience.
Neurons
A neuron (also known as a neurone or nerve cell) is a specialized cell that processes and transmits information along its surface via electrical (ionic) signals. Neurons can signal other neurons and muscles via synapses, connections with other cells. Neurons come in two basic types; excitatory and inhibitory. Excitatory neurons increase electrical excitability of other neurons whereas inhibitory neurons decrease electrical excitability of other neurons. Neurons are the core components of the brain and spinal cord of the central nervous system. A drawing of neurons
Networks of Neurons
In the brain and spinal cord neurons connect to each other and to themselves to form biological neural networks. These networks of living neurons are constantly active and typically maintain a balance between excitation and inhibition via chemical synapses. Networks of neurons can range in size from 2 neurons to billions.
EEG
Electroencephalography (EEG) is a method of monitoring the electrical activity of networks of neurons in the brain. EEG measures average voltage fluctuations resulting from ion flow in networks of neurons. In clinical contexts, EEG refers to the recording of the brain's electrical activity over a period of time. EEG is typically recorded from multiple electrodes placed on the scalp, but can be recorded from electrodes on or in the brain. Diagnostic applications generally focus on the frequency content of EEG, that is, the type of neural oscillations (brain waves) that can be observed in EEG signals.
Seizure
A seizure (from the Latin sacire—to take possession of) is the clinical or behavioural manifestation of an abnormal, excessive and hypersynchronous discharge of a population of neurons that is observed on an EEG. Seizures can be evoked in all animals with true brains via several means including drugs that either reduce inhibition or increase excitation.
Epilepsy
Epilepsy is a chronic neurological disease in which the brain has an increased predisposition to generate transient hypersynchronous and hyperexcitable neural network events - seizures. What distinguishes an epileptic brain from a typical brain is the relative ease with which stimuli can elicit a seizure - a low seizure threshold. Individuals vary with respect to their seizure threshold and that threshold also varies over different time scales; lifetime, monthly, and the sleep/wake cycle with the lowest seizure thresholds occurring in the very young and aged, during menstruation and ovulation and sleep.
The brains of individuals with epilepsy have a seizure threshold that is so low that innocuous sensory stimuli, such as flickering lights, can trigger seizures. Seizures can also be self-generating (spontaneous) without any obvious externally applied provoking stimulus, although presumably some internal causal event (like changes in blood flow and blood pressure) triggers the seizure. Anti-seizure drugs (also known as anti-convulsant drugs or anti-epileptic drugs) work by raising seizure thresholds thus reducing the likelihood that a seizure will occur.