While most people experience subtle changes in memory function as they grow older, extreme changes concern a relatively small proportion of people. Subtle changes in memory function known technically as mild cognitive impairment (MCI) usually occur in geriatric population and are more serious than ordinary memory lapses or forgetfulness, such as misplacing things and having difficulty recalling words. Although at first MCI doesn’t interfere with the activities of daily life, it can be a precursor of dementia including Alzheimer’s disease (AD) and lead to a large-scale memory loss known as amnesia. Amnesia can also be caused by, among others, traumatic experiences, brain injury, alcohol or drug abuse, hypoxia, seizures, or psychological disorders (e.g. depression and anxiety).

Basically, there are two types of amnesia: retrograde amnesia and anterograde amnesia. Retrograde amnesia (RA) is when an individual can’t recall memories that occurred before the event that caused the condition, but he/she can still lay down new memories. The loss of the ability to form new memories (i.e. transferring new information into permanent storage) after the event is something altogether different. When this happens, we are dealing with anterograde amnesia (AA).

Picture of the hippocampus
The human hippocampus and fornix (left) compared with a seahorse (right): Wikipedia

A vital role in transferring information from short-term to long-term memory is played by a part of the brain called the hippocampus (named after a seahorse, a tiny fish in the genus Hippocampus, which is what it looks like). Before the 1950s it had not been known that the hippocampus was essential for learning and memory and that its destruction causes amnesia. It was only established to be responsible for memory consolidation by the case of Henry Molaison, known also as patient H.M.

The common difficulty of remembering childhood experiences that occurred before the age of 2–4 years is sometimes referred to as childhood (or infantile) amnesia. Childhood amnesia is attributable to the immaturity of the neurological system of the infant brain, although other explanations have been proposed.

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