Definition
Merriam-Webster Online Dictionary (2009 [3]) defines seizure as "a: a sudden attack (as of disease) ; especially: the physical manifestations (as convulsions, sensory disturbances, or loss of consciousness) resulting from abnormal electrical discharges in the brain (as in epilepsy) b: an abnormal electrical discharge in the brain”.
Seizure: "Uncontrolled electrical activity in the brain, which may produce a physical convulsion, minor physical signs, thought disturbances, or a combination of symptoms”, (Medical Dictionary 2004 [2]).
Gelb (2005[1]) defines seizure as "an episode of altered behaviour or sensorium caused by excessive and hypersynchronous discharge of neurons".
Theoretical frame
(Source: Wikipedia, 2009)
The occurrence of a seizure is a function of abnormal neuronal hyperactivity. Seizures are best known with jacksonian spread in which patient shows unusual motor activity, such as jerking of muscles, in a portion of one limb. Generally, such symptoms spread over one side of the body in an analogous fashion consistent with body’s cortical motor strip. While visual illusions of different types may occur as a result of seizure in the occipital cortex, olfactory hallucinations may occur with seizures in temporal cortex. Limbic cortex seizures result in more complex symptoms such as feeling of dissatisfaction, overwhelming, feeling of depersonalization or mixes of these. Different types of seizures are known according to the area of the brain and nervous system the seizure hits (Gelb (2005[1]) .
1. Partial Seizure
Partial seizure is that which originates in the focal region of a single hemisphere of the brain. Partial seizures sometimes results in uncontrolled consciousness because of the involvement of the limbic system. These seizures only last for 2-3 minutes. This type of partial seizure is called complex partial seizure. Partial seizures that do not affect consciousness are called simple partial seizures. When partial seizures spread over two hemispheres of the brain (partial seizure with secondary generalization), it results in altered consciousness of the involvement of bilateral hemisphere.
2. Generalised Seizures
Seizures involving both cerebral hemisphere from outset is called Generalised Seizures. There are six common known generalized seizures. Firstly, Tonic seizures occur due to sudden muscular contraction resulting on rigid extension or flexion. Secondly, Generalized tonic-clonic seizure occurs without any prior warning. An epileptic rigidity may occur as a result of tonic spasm in truncal muscles followed by jerking movements. This seizure may not last for more than 1-2 minutes. Thirdly, Clonic seizure occurs with no initial tonic phase and involve rhythmic jerking of muscles. Fourthly, Atonic seizures are characterised by a brief loss of muscle tone. This can be genralised and result in a fall or ir can be localsed and produce focal loss of postural control, such as a head-drop. Finally, while Absence seizure (petit mal seizures) begins with a blank look, shaking of eyelids, unresponsiveness, myoclonic seizure involves rapid rhythmic jerking movements of muscles. One of myoclonic seizure is limb movement while asleep.
Seizures and Aviation
Due to safety reasons all aviators, especially military pilots, are screened for seizures before employment and on a regular basis over the flying period. This is because, seizures are considered as a ‘threat’ to aviation - there is a great chance resulting in a crash particularly in single-man operations. Moreover, if a pilot is positive for a seizure, he is grounded until he shows no sign of early or late stages of seizure. Subsequently, seizures in aviation are uncommon.
Supporting evidence
An aviation accident involving a seizure was reported last year. An experienced 36 year old military pilot with 4,000 flying hours, was hit by a seizure on the ground during a helicopter engine and rotor test. The pilot was trying to realign the helicopter into the wind. One of the ground crew noted that the pilot’s behaviour was abnormal. When the ground crew instructed to activate some switches on the lower console, the pilot was confused looking at upper console. The pilot lost consciousness and the helicopter uncontrollably rolled over to its left side. After 20 minutes the pilot regained his consciousness but had no memory of what had happened. He was observed by neurologists and was found to be at the state of post-seizure (Simon, Watts, & Bohnker, 2008[4]).
