Overview
Amnesia is a loss of memory or information connected to physical or psychological trauma. Contrary to stereotypical media portrayals of amnesia, it is not associated with a huge change in personality, identity, or intelligence. Amnesia tends to be categorized as either retrograde amnesia, meaning memory loss before the date of a traumatic event, or anterograde amnesia, meaning an inability to form new memories for long-term use. More specific labels can be used as well: transient global amnesia for a sudden onset of temporary memory loss, dissociative amnesia associated with stress and loss of personal information, childhood amnesia over recalling memories of early life (which isn’t uncommon), and post-traumatic amnesia after some kind of damaging neurological event leads to disorientation and confusion. It is also possible for someone to experience a combination of these or for amnesia to present in a complex form that operates at different layers.
Substance use can also trigger episodes of amnesia; drinking until blacked out is a form of drug-induced anterograde amnesia where someone might be awake and conscious with access to past memories but no ability to transform short-term memory into long-term memory. Blackouts are often described as either fragmentary blackouts with bits and pieces being remembered, in which case some people refer to them as “brownouts,” or en bloc blackouts where no memories at all are recorded over some period of time. This generally happens because substances like alcohol and marijuana directly impact the receptors in the hippocampus region of the brain, which plays a dominant role in filing memories into long-term storage. In severe cases of chronic substance use, permanent amnesia can set in through conditions like Wernicke-Korsakoff syndrome which has a comparable memory loss pattern to dementia.
At the same time, people who suffer from dissociative amnesia after traumatic events can turn to substance use as a form of self-medication. Dissociative amnesia is thought to be a form of psychological self-defense in which the brain blocks out traumatic memories that are too overwhelming to process, but it doesn’t prevent the confusion or distress that arises from experiencing that dissociation. Amnesia in general weakens someone’s ability to recall information from the past that would be relevant for future choices, which can impact how individuals choose to use substances despite past consequences. The brain leans increasingly on unconscious and automated habits that can involve substance use.