Long-Term Amnesia Research Team

What is Long-Term Amnesia (LTA)?

Amnesia is a general term referring to any partial or complete loss of memory. There are many forms, which may occur separately or in combinations. A common distinction is between retrograde and anterograde forms. Retrograde amnesia refers to loss of memories for events which occurred prior to the onset of the condition, while anterograde amnesia is an inability to lay down new long-term memories.

Well publicised cases such as the American patient known as “HM”, or the British musician Clive Wearing, suffer from a combination of symptoms known as “classical amnesic syndrome”. They typically display a limited degree of retrograde amnesia, with many memories of their early life intact, but suffer from severe anterograde amnesia, with all memory for new information or events completely lost within a few minutes.

However, cases are now emerging of anterograde amnesia with a much later onset. Such patients can form new memories in a normal manner, and can retain information for several days, but then suffer an accelerated forgetting, often losing all memories for new events within a few weeks. As a typical example, a patient may return from a foreign holiday with intact memories for the places and things they have seen, but some months later have no recollection of having ever been to that part of the world. Such late onset anterograde amnesia is referred to as Long-Term Amnesia (LTA).

Isn’t LTA just mild classical amnesia?

It could be argued that the accelerated forgetting shown in LTA is just a milder form of the anterograde amnesia displayed by classical amnesiacs. However, the evidence from brain lesion studies suggests this is unlikely. Classical amnesia is typically caused by brain damage in the area of the brain known as the medial temporal lobe, especially the area referred to as the hippocampus. In contrast LTA patients typically display brain damage in different areas (e.g., the anterior temporal lobe), and there are no confirmed cases of hippocampal damage in LTA patients. It therefore appears that LTA is a distinct condition.

How does LTA affect peoples’ lives?

Any form of amnesia can be distressing for both patients and their families. Loss of memories for past events makes it difficult to relive or reminisce about events with others. Sufferers may be unable to remember what was discussed in a previous conversation or meetings with others, and to avoid repeating themselves may become withdrawn in social situations. Patients may have to adopt various strategies to limit the impact of their condition, such as making notes about important conversations and maintaining detailed diaries. They may also be unable to retain routes for getting around a new town or city if they move home, and may be unable to navigate alone.

Why is LTA worth studying?

Clinically, the existence of LTA challenges the standard neuropsychological memory tests used in clinical practice. Such tests look at memory retention over delays of up to 30 minutes, the assumption being that if you have retained information that long then you have no memory problems. However LTA patients will pass such tests with flying colours, but will then suffer accelerated forgetting later. Such cases confirm that it is possible to pass the standard tests but still have a significant memory problem.

Theoretically, LTA is important for understanding memory consolidation. Consolidation refers to the process by which information held temporarily in short term or working memory is converted into a form in which it can be retained for long periods, perhaps even indefinitely. Early theories of consolidation assumed such a transfer from short-term to long-term memory happened in a single stage, completed in several minutes; hence the clinical belief that if your memories are intact at 30 minutes then you have no memory problems. Later theories suggest this transfer occurs in multiple stages, which continue for months or even years. LTA provides valuable evidence for such theories; it points to the failure of a secondary consolidation process that occurs days or weeks after the event.

Current studies with LTA patients have indicated that repeated recall or retrieval of information improves consolidation and helps to make memories immune to accelerated forgetting. Evidence arising from such research studies may eventually form the basis of memory strategies to help patients limit the impact of the condition.

What is known about the causes of LTA?

The cause of LTA is still unclear. Study of the cases reported so far has identified two possible contributory factors. The first is damage to the front section of the temporal lobe, known as the anterior temporal lobe. The second is temporal lobe epilepsy. All of the cases reported show at least one of these, with several cases showing both. However the mechanism of LTA is not yet understood, and it may be that multiple factors can trigger the condition, including other factors not yet identified.

What research is the UEL team doing?

The research team at UEL have been working with one confirmed LTA case over a period of 5 years. This patient passes the standard clinical tests and clinicians initially refused to believe he had any significant memory problems. Studies at UEL identified clear evidence of LTA, after which more detailed neuropsychological testing diagnosed temporal lobe epilepsy. We are now looking for further cases, and intend to further investigate the role of epilepsy in LTA. In 2004, Ashok Jansari won the International Neuropsychological Society’s Cermak Prize for best research in memory disorders at their conference in Brisbane, Australia for the work that he had been doing on LTA.

How can I get involved?

As we are keen to identify further cases of LTA please contact us if you, or someone you know, suffers from symptoms similar to those described above. In addition we are always looking for “control subjects”, people with no memory problems who act as comparisons; please get in touch if you would like to take part in research on that basis.

Recent publications from the LTA Research Team:

McGibbon, T.I., Jansari, A.S., & Gaskell, G. (2008). Say it again? The importance of repeated recall for ensuring consolidation in ‘longterm amnesia’ (LTA). Journal of the International Neuropsychological Society, 14(2), 70–71.
Jansari, A., Davis, K., Firminger, S., Ward, T., & Kapur, N. (2005). When long-term memory does not necessarily mean “forever”: evidence of long-term amnesia in a patient with temporal lobe epilepsy. Journal of International Neuropsychology, 4(10), 26.