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Retrograde amnesia involves losing memories formed before the condition's onset, as seen when NFL player Scott Bolzan lost all past memories after a head injury. Anterograde amnesia prevents forming new memories after onset, as experienced by Henry Molaison after epilepsy surgery. Both impair long-term memory but affect different time periods.

The hippocampus is critical for forming new memories. When parts of the hippocampus are damaged or removed, as in H.M.'s case, anterograde amnesia results. The role of hippocampus in memory formation explains why damage to this brain region severely impairs the ability to retain new information.

Amnesia results from multiple causes including traumatic brain injuries, psychological trauma, neurodegenerative diseases like Alzheimer's, and substance abuse. The severity and duration of memory loss depend on the underlying cause and type of amnesia. Each cause affects memory systems differently, requiring individualized assessment.

Infantile amnesia is the inability to recall events from the first two to three years of life. This occurs because the hippocampus is underdeveloped during infancy, preventing proper encoding and storage of memories. This is a normal phenomenon affecting most people during early development.

Diagnosis involves neuropsychological assessments, brain imaging, and patient history review to identify the amnesia type and underlying cause. While no cure exists, cognitive therapy and memory aids like notebooks improve daily functioning. For neurodegenerative cases, medications may slow cognitive decline but cannot restore lost memories.

Transient global amnesia is a sudden, temporary memory loss that usually lasts a few hours. It typically arises from stress or abrupt environmental changes. Unlike other amnesia types, this condition is temporary and usually resolves without producing long-term memory impairment.

Brain structures including the cerebellum and prefrontal cortex support memory consolidation and retrieval processes. Damage to these regions can worsen amnesia severity and impair recovery. Understanding the role of cerebellum and prefrontal cortex in memory helps explain why different brain injuries produce varying amnesia types.