Transient global amnesia (TGA) is a neurological disorder whose key defining characteristic is a temporary but almost total disruption of short-term memory with a range of problems accessing older memories. A person in a state of TGA exhibits no other signs of impaired cognitive functioning but recalls only the last few moments of consciousness and, possibly, a few deeply encoded facts of the individual's past e.g., their childhood, family, or home. Both TGA and anterograde amnesia deal with disruptions of short-term memory. However, a TGA episode generally lasts no more than 2 to 8 hours before the patient returns to normal with the ability to form new memories.
Signs and symptoms A person under TGA has almost no capacity to establish new memories, but generally appears otherwise mentally alert and lucid, possessing full knowledge of self-identity and identity of close family, and maintaining intact perceptual skills and a wide repertoire of complex learned behavior. The individual simply cannot recall anything that happened outside the last few minutes, while memory for more temporally distant events may or may not be largely intact. The degree of amnesia is profound, and, in the interval during which the individual is aware of their condition is often accompanied by anxiety. The diagnostic criteria for TGA, as defined for purposes of clinical research, include:
The attack was witnessed by a capable observer and reported as being a definite loss of recent memory (anterograde amnesia). There was an absence of clouding of consciousness or other cognitive impairment other than amnesia. There were no focal neurological signs or deficits during or after the attack. There were no features of epilepsy, or active epilepsy in the past two years, and the patient did not have any recent head injury. The attack resolved within 24 hours.
Progression of a TGA event This onset of TGA is generally fairly rapid, and its duration varies but generally lasts between 2 and 8 hours. A person experiencing TGA has memory impairment with an inability to remember events or people from the past few minutes, hours or days (retrograde amnesia), and has working memory of only the past few minutes or less, and thus cannot retain new information or form new memories beyond that period of time (anterograde amnesia). One of its notable features is perseveration, in which the victim of an attack faithfully and methodically repeats statements or questions, complete with profoundly identical intonation and gestures "as if a fragment of a sound track is being repeatedly rerun." This is found in almost all TGA attacks and is sometimes considered a defining characteristic of the condition. The individual experiencing TGA retains social skills and older significant memories, almost always including knowing his or her own identity and the identity of family members, and the ability to perform various complex learned tasks including driving and other learned behavior; one individual "was able to continue putting together the alternator of his car." Also, during episodes of TGA, a person's personality remains intact and the episode is not associated with loss of consciousness, a decreased level of consciousness or cognitive deficits (other than memory impairment). Though outwardly appearing to be normal, a person with TGA is disoriented in time and space, perhaps knowing neither the year nor where they reside. Although confusion is sometimes reported, others consider this an imprecise observation, but an elevated emotional state (compared to patients experiencing transient ischemic attack, or TIA) is common. In a large survey, 11% of individuals in a TGA state were described as exhibiting "emotionalism" and 14% "fear of dying". The attack lessens over a period of hours, with older memories returning first, and the repetitive fugue slowly lengthening so that the victim retains short-term memory for longer periods. This characteristic of TGA, where the length of time affected by retrograde amnesia shortens (i.e. older memories return first, followed by more recent memories) is commonly seen. In the majority of cases there are no long-term effects other than a complete lack of recall for this period of the attack and an hour or two before its onset. However, while seemingly back to normal within 24 hours, there are subtle effects on memory that may persist longer. There is emerging evidence for observable impairments in a minority of cases weeks or even years following a TGA attack.
Causes The underlying cause of TGA remains enigmatic. The leading hypotheses are some form of epileptic event, a problem with blood circulation around, to or from the brain, or some kind of migraine-like phenomenon. The differences are sufficiently meaningful that transient amnesia may be considered a heterogeneous clinical syndrome with multiple etiologies, corresponding mechanisms, and differing prognoses.
… excerpt ends here. Continue reading the full article.
