Glossary

Alzheimer’s disease (AD) A degenerative brain disorder usually (but not always) afflicting the elderly, which first appears as an impairment of memory but later develops into a more general dementia.

Amnesia A pathological impairment of memory function.

Anterograde amnesia (AA) Impaired memory for events which have occurred since the onset of the disorder (contrasts with retrograde amnesia).

Confabulation The reporting of memories which are incorrect and apparently fabricated, but which the patient believes to be true.

Declarative memory Memory which can be reported in a deliberate and conscious way (contrasts with procedural memory).

Diencephalon A brain structure which includes the thalamus and hypothalamus. Parts of the diencephalon are involved in processing and retrieving memories, and damage to these structures can cause amnesia.

Electroconvulsive therapy (ECT) A treatment used to alleviate depression which involves passing an electric current through the front of the patient’s head.

Extended hippocampal complex A system of interconnected structures within the brain, incorporating the hippocampus, anterior thalamus and mammillary bodies, which is involved in the encoding and storage of new memory traces.

Herpes simplex encephalitis (HSE) A virus infection of the brain, which in some cases leaves the patient severely amnesic.

Hippocampus A structure lying within the temporal lobes, which is involved in the creation of new memories. Hippocampal lesions usually cause impairment of memory, especially the storage of new memories.

Korsakoff’s syndrome A brain disease which usually results from chronic alcoholism, and which is mainly characterised by a memory impairment.

Organic amnesia An impairment of memory function caused by physical damage to the brain.

Procedural memory Memory which can be demonstrated by performing some skilled procedure such as a motor task, but which the subject is not necessarily able to report consciously (contrasts with declarative memory).

Psychogenic amnesia A memory impairment of psychological origin.

Rehabilitation Strategies used to help patients to cope with an impairment or disability, enabling them to function as effectively as possible within the limitations created by the impairment.

Retrograde amnesia (RA) Impaired memory for events which occurred prior to the onset of amnesia (contrasts with anterograde amnesia).

Summary

• Organic amnesia is caused by brain damage, usually affecting the temporal lobes, hippocampus, and anterior thalamic nuclei.
• Such brain lesions may arise from a variety of different causes, such as Alzheimer's disease, Korsakoff's syndrome, Herpes Simplex Encephalitis, strokes, and tumours.
• Organic amnesia is characterised by an impairment of long-term memory, but the short-term working memory usually remains intact.
• Most amnesics suffer from anterograde amnesia, so that they have difficulty in learning new information from the time period subsequent to onset.
• Many amnesics also suffer from retrograde amnesia, in which memories are also lost from the period preceding onset. However, the retrograde impairment may be fairly limited, and memories for earlier time periods such as childhood often remain intact.
• The anterograde and retrograde components of amnesia appear to be fairly independent of one another, so that their relative severity can vary considerably from patient to patient. In rare cases either retrograde or anterograde amnesia may occur in isolation.
• Most amnesics suffer a severe impairment of conscious declarative and explicit memory processes such as the recollection of events and contextual associations, but there is usually no impairment of non-declarative and implicit memory processes such as motor skill learning, priming, and familiarity judgements.
• In addition to the amnesias which are characteristic of the organic amnesic syndrome, memory impairment may also be caused by other factors, such as concussion, electro-convulsive therapy, ageing, and psychogenic causes. However, these impairments tend to have their own distinct characteristics, and differ somewhat from the pattern of organic amnesic symptoms.
• Although brain lesions are usually irreversible, many rehabilitation strategies have been devised to help organic amnesics to cope with their memory impairment.

Weblinks

Memory systems
http://thebrain.mcgill.ca/flash/a/a_07/a_07_p/a_07_p_tra/a_07_p_tra.html#3

Anatomy of memory
http://www.exploratorium.edu/memory/braindissection/index.html

What happens when you remove the hippocampus? Video, discussion and questions on how Alzheimer’s affects the brain

What is Alzheimer’s disease?
https://ed.ted.com/lessons/what-is-alzheimer-s-disease-ivan-seah-yu-jun

Are all your memories real? Daniel L. Schacter discusses the fallibility of memory through an animated video, complemented by discussion topics and questions
https://ed.ted.com/lessons/are-all-of-your-memories-real-daniel-l-schacter

Multiple Choice Questions