Transient epileptic amnesia (TEA) is a rare but often underdiagnosed neurological condition characterized by relatively brief, recurrent episodes of amnesia due to underlying temporal lobe epilepsy. Although the descriptions of the condition are based on fewer than 100 cases published in the medical literature, and the largest single study to date involved 50 people with TEA, TEA has considerable theoretical significance and competing theories of memory in humans attempt to reconcile its findings. People with TEA have a severe decline in short-term memory, so that they have great difficulty recalling events in the few minutes preceding the attack, or events in the hours before the onset of the attack, and even memories of important events in recent years may be absent during the amnesic episode. Some patients report short-term retrograde amnesia, causing them to not recognize their home or family members, although they are aware of their own identity. The onset of TEA is sudden. Three-quarters of reported cases have been reported upon awakening. In attacks that begin while fully awake, olfactory hallucinations, a “strange taste” or nausea are reported. Less than half of cases involve olfactory or gustatory hallucinations, and more than a third involve involuntary movements. A quarter of attacks involve a brief period of unresponsiveness. However, in most cases there are no warning signs. During an attack, the patient’s cognitive function is generally unaffected; perception, communication and attention are normal for most of the attack. In half of the reported cases, behaviour involves repetitive questioning as the brain fails to form new memories or retrieve a range of recent experiences. The UK’s Memory Loss in Epilepsy website describes an attack as follows: During an attack, the patient loses the ability to remember things that happened in the past days or weeks. Sometimes, the amnesia can affect events that happened in the past. The person often has difficulty storing new information and may repeat the same question, such as “What day is it today?” or “What are we supposed to do today?” However, the patient does not lose their sense of who they are and can often recognise close friends or relatives. The person's physical appearance usually remains normal. Observers may notice pale skin, brief "aphasic loss of communication" such as not being aware of the person witnessing the attack, or involuntary movements such as swallowing, lip smacking, or hand fidgeting. But in most cases, the patient responds appropriately to the condition. He or she can continue conversations and perform activities such as dressing, walking, or even playing golf. Attacks typically last 20–60 minutes. Some attacks may last less than five minutes. Much longer attacks have been reported; in a 2007 study of 50 cases of transient epileptic amnesia, one lasted four days and another two days. These unusual cases "may be due to ongoing seizure activity or to persistent post-ictal dysfunction of memory-related brain structures." Transient amnesia can be the primary manifestation of epilepsy. However, doctors rarely suspect the diagnosis and it remains controversial. Transient epileptic amnesia is frequently misdiagnosed, according to one leading authority. In the largest study to date, “epilepsy was the primary diagnosis in only 12 of the 50 cases.” Diagnosis is complicated by the fact that more than a third of cases have normal EEG readings after the attack. However, because TEA recurs on average 12 times a year, witnesses and physicians may be able to recognize the condition retrospectively; the average delay in diagnosis of TEA in a 2007 study was 12 months. TEA is a form of focal seizure, “the most common type of epilepsy in adults,” unlike tonic-clonic or grand mal seizures, in which sufferers lose consciousness and convulse. Diagnostic criteria for the disorder were established in a 2007 study of 50 confirmed cases based on clinical features that distinguish transient epileptic amnesia from transient global amnesia, with which transient epileptic amnesia is often compared: Transient epileptic amnesia responds well to low doses of antiepileptic drugs, resulting in cessation of seizure activity in 45 of 47 patients. The frequency of seizures decreased in patients treated with these drugs. However, no cases of recovery of lost memory were reported, although there have been suggestions that the rate of memory decline may be improved with these drugs.