Seizures are caused by a disruption in the brain's electrical activity, which affects neural communication. The Merck Manual Online Medical Library defines two types of seizures: epileptic and nonepileptic. Epileptic seizures, also referred to as epilepsy and seizure disorders, do not have a specific cause; epileptic seizures occur frequently. Nonepileptic seizures, on the other hand, are triggered by an abnormality in the patient's brain. Patients with nonepileptic seizures might have only one episode.
Previous Brain Damage
In cases of nonepileptic seizures, the change in electrical activity is caused by previous brain damage. Examples of brain damage that can trigger nonepileptic seizures are brain infections, inadequate oxygen to the brain, brain tumors, stroke, head injuries and cerebral edema (swelling of the brain). The Merck Manual Online Medical Library notes that in response to these abnormalities in the brain, a single seizure is provoked. While seizures caused by these brain injuries do not result in further brain deterioration, they can cause confusion, loss of consciousness and convulsions. However, if the initial problem is not treated, patients can continue to have seizures.
Cognitive Decline
In Dr. Donna C. Bergen's commentary, "Do Seizures Harm the Brain," she mentions studies that investigated the effects of seizures on cognition, which includes memory, attention, learning and decision making. In a study conducted by Thompson and Duncan, which Bergen was commenting on directly, the researchers found that patients with generalized tonic-clonic seizures (seizures that involve the whole body), had a decline in both memory and decision making skills; the patients' IQs, on the other hand, remained unaffected. In another study by Andersson-Roswall et al, Bergen mentions that patients with partial epilepsy had a decline in retention of verbal and visual-spatial information. The patients who experienced problems with cognition were diagnosed with epileptic seizures, not nonepileptic seizures.
Localization
Dr. Bergen notes in her commentary that localized damage also can occur with specific types of seizures. In a study by Tasch et al, imaging was done on seizure patients to pinpoint the effects of seizures on their brains. When examining patients with temporal lobe epilepsy, an MRI scan showed a reduction in the volume of hippocampus, a brain structure crucial to memory. Using MR spectroscopy, researchers also found that patients with tonic-clonic seizures had a decreased amount of the neuronal marker N-acetylaspartate. Like the studies on cognitive decline, damage to the brain was only found in patients who had a high frequency of seizures.
