Loss of the
ability to memorize information and/or recall information stored in memory.
Amnesic conditions affect mainly long-term memory (where information is
retained indefinitely) rather than short-term memory (where it is only retained
for seconds or minutes).
Many people
with amnesia have a memory gap that extends back for some time before the onset
of the disorder.
This
condition, known as retrograde amnesia, is principally a deficit of recall. In
the majority of cases, the memory gap gradually shrinks over time.
Some people
with amnesia are unable to store new information in the period following the
onset of the illness. The resultant gap in memory, known as anterograde
amnesia, extends from the moment of onset of the amnesia to the time when the
long-term memory resumes (if at all). This memory gap is usually permanent.
CAUSES
Amnesia is
the result of damage to, or disease of, regions in the brain that are concerned
with memory function. Possible causes of such damage are head injury;
degenerative disorders such as Alzheimer’s disease and other forms of dementia;
infections such as encephalitis; thiamine deficiency in problem drinkers, which
leads to Wernicke–Korsakoff syndrome; brain tumours; strokes; and subarachnoid haemorrhage.
Amnesia can also occur in some forms of psychiatric illness (in which there is
no apparent physical damage to the brain). Some deterioration of memory is a
common feature of aging.
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