Transient global amnesia is a neurological disorder that primarily involves a temporary but near-complete impairment of short-term memory and difficulty recalling old memories. A patient with transient global amnesia shows no other signs of impaired cognitive functioning, but remembers only the last few moments before losing consciousness, plus some encoded facts about his or her past, such as his or her childhood, family, or sometimes home. Both transient global amnesia and anterograde amnesia deal with short-term memory disorders; however, an episode of transient global amnesia generally lasts no more than 2 to 8 hours before the patient returns to normal with the ability to form new memories. A patient with anterograde amnesia may be unable to form new memories indefinitely. A person with transient global amnesia is temporarily unable to form new memories, but is generally in a balanced state of mind, has full knowledge of self and immediate family, maintains intact cognitive skills, and has a broad capacity for complex cognition and behavior. The individual simply cannot remember anything that happened beyond the past few minutes, while memory for distant events may or may not be largely intact but only temporarily. The degree of memory loss is profound, and when the patient is aware of his or her condition, it will often be accompanied by anxiety. Clinical diagnostic criteria for transient global amnesia include: Transient global amnesia generally begins rapidly, and its duration varies but generally lasts between 2 and 8 hours. A person with transient global amnesia has memories of the past few minutes or less, and cannot retain new information beyond that time period. One of its peculiar features is persistence, in which the patient repeats phrases or questions with complete fidelity and method, with identical intonations and gestures (similar to replaying a track over and over again), which occurs in almost all cases of transient global amnesia and is sometimes considered a defining feature of the condition. A person with transient global amnesia retains important social skills and older memories, including knowledge of his or her own identity and that of family members, and the ability to perform complex learned tasks such as driving and learned behavior, as one patient was able to continue assembling his car's generator. Despite appearing to be in good health, a person with transient global amnesia is disoriented in time and place, and may not know the year or where he or she lives. Although confusion has been reported occasionally, and some consider this observation to be inaccurate, heightened emotional states are common. According to a large survey, 11% of transient global amnesia patients described feeling emotional and 14% were afraid of dying. The condition becomes less severe over hours, old memories return first, amnesia becomes shorter, and the victim retains short-term memory for longer periods. Although the patient returns to normal within 24 hours, there are actually mild effects on memory that may last longer. In most cases, there are no long-term effects other than complete loss of memory for the period of time the patient experienced the condition and the hour or two before it began. In some cases, there is clear evidence of noticeable damage weeks or even years after the onset of transient global amnesia. There is also evidence that the victim knows something is not quite right, although they cannot pinpoint what it is. Sometimes patients show signs during the condition that they know they have just lost their memory, or that they believe they have had a stroke, although they are unaware of the other signs they are experiencing. The main sign of the condition is that they repeatedly do and say things that would not normally happen. The cause of transient global amnesia remains unclear. The main hypotheses are that the patient has a form of epilepsy, a problem with the blood circulation to or from the brain, or a migraine. Differential diagnosis is important in order to classify transient global amnesia as a heterogeneous clinical syndrome with multiple etiologies, mechanisms, and prognoses. Transient global amnesia attacks are associated with some form of precipitating event in at least one-third of cases. The most common precipitating events include vigorous exercise, swimming in cold water or exposure to temperature changes, and traumatic or stressful emotional events. There have been reports of transient global amnesia-like episodes occurring during certain medical procedures and medical conditions. One study reported two familial cases, in which two members of the same family experienced transient global amnesia, out of 114 cases. This suggests a small probability that transient global amnesia is a familial occurrence. When the definition of precipitating events is expanded to include events occurring days or weeks prior, and stressful burdens such as financial worries, attending a funeral, or being overwhelmed by fatigue or childcare responsibilities, the vast majority of transient global amnesia attacks will be associated with precipitating events. Some research has examined the role of common psychological factors, as people with TGA show high levels of anxiety and/or depression. Emotional instability may leave some people vulnerable to stress and thus be associated with TGA. When compared to patients who have had TGA, TIA patients are more likely to have some form of emotional problem in their personal or family history, or to have previously suffered from some form of phobia. Cerebral ischemia is a potential cause that is often disputed, at least for some TGA patients. Until the 1990s, TGA was thought to be a secondary form of TIA that occurred as a result of some form of cerebrovascular disease. Those who argue against vascular causes justify their position by saying that TGA patients are no more likely than the general population to develop cerebrovascular disease later on. In fact, compared to TIA patients, TGA patients have a significantly lower risk of stroke, myocardial infarction, and death from these events. However, other vascular causes are still possible. According to research into jugular vein valve insufficiency in patients with transient global amnesia, transient global amnesia in these cases had an important effect. One current hypothesis is that transient global amnesia may be caused by cerebral venous congestion, leading to hypoperfusion of brain regions associated with memory, such as the hippocampus. It has been shown that performing the Valsalva maneuver may help to induce retrograde blood flow in the jugular vein, thus restoring normal blood circulation in these patients.