http://teddysratlab.blogspot.com [Full link to blog for email clients.][FT:C44]
To follow up on the discussion of stroke and TIA (transient ischemic attacks)... Repeated ischemia can leave scar tissue that is prone to unpredictable electrical activity. The irony is that such unpredictable activity is in fact quite ... synchronized. The EEG traces at right show the random, irregular pattern of normal brain activity at first, then large, synchronous pattern of seizure activity for 5-10 seconds, and a return to normal EEG.
So - what is a seizure?
Most people, upon hearing the term, think of convulsions and epilepsy. However, seizures do not have to involve convulsions, and not all seizures or convulsions indicate epilepsy.
Definitions: A seizure is an episode of periodic, synchronous activity in brain cells that normally do not fire synchronously. A convulsion results from a seizure that involves the motor cortex, resulting in muscle twitches or spasm. Epilepsy is a disease of recurrent seizures - with or without convulsions - that originate in the same area of brain.
Seizures can be one-time events or recurrent - even without a diagnosis or epilepsy. They can be caused by scar tissue from stroke or TIA, from head injury, vascular irregularities, congenital defect or none of the above. Convulsions can result from seizure, infection or fever - anything that causes the motor cortex to fire the neurons out of sequence. A diagnosis of epilepsy generally only comes once seizures are diagnosed as recurring uncontrollably, do not respond to baseline medications, and involve an altered state of consciousness. In this manner, tics, spasms, tinnitis and optic flashes are all forms of seizure (if they originate in the brain) with no stigma of epilepsy involved.
Convulsions come in many different types - the petit mal seizure evokes hardly any muscle twitch, while the grand mal can involve muscle spasm throughout the whole body. Partial seizures may involve a single limb - right hand and arm up to the elbow, for example - or perhaps part of the face. Complex seizures progress from one area of the brain to another - thus producing a "march" of convulsions until they involve the whole body. [A "complex-partial" seizure starts as a partial seizure - generally involving a single limb, then progresses to whole body convulsion.]
The next blog will complete the discussion by exploring the various forms of epilepsy, with discussion about medication, diagnosis and the lifestyle impacts of seizures.