Amnesia

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In the movie The Bourne Identity, CIA assassin Jason Bourne tells his new acquaintance Marie Kreutz about washing up on shore, unconscious, with two bullets in his back.
He tells her that he can’t remember anything that happened before regaining consciousness, saying [Jason: No, I’m serious.
I don’t know who I am, I don’t know where I’m going, none of it.] Jason Bourne has amnesia which refers to lacking memory.
Now, memory can be divided into two main types. The first is implicit memory, also known as procedural memory.
Procedural memory refers the sorts of skills you do automatically, without thinking much about it. For example, walking, riding a bike, or texting for most teenagers--anything that has become a habit.
The second type of memory is explicit memory, also known as declarative memory. Declarative memory refers to retaining facts--the sort of stuff you need to win a trivia contest.
And these memories do take conscious effort to retrieve. When trying to remember things like, “how many countries start with the letter J?”, most of us need to stop and focus.
It’s three by the way. You can think of procedural memory as “remembering how,” and declarative memory as “remembering what.” When we talk about amnesia, we really mean that some part of a person’s declarative memory, the “remembering what” is affected.
Jason Bourne may not remember who he is, but he has no problem remembering how to speak foreign languages or how to fight.
Now, the process of making declarative memory can be broken down into four stages, and each stage involves specific parts of the brain.
The first stage is encoding, and it occurs in the prefrontal cortex. Encoding begins right when you first sense something.
Say you’re tasting a strawberry. Encoding would involve classifying the strawberry according to sweetness, size, color and texture.
Think of encoding as a process of breaking down an experience into a manageable parts for rest of the brain to use. The second stage is consolidation.
Consolidation occurs in the hippocampus, which is deep within the temporal lobes. In consolidation, the encoded bits of information like sweetness, size, and texture of the strawberry are linked up to existing memories.
Think of consolidation as solidifying the memory. Comparing that information about the strawberry with memories you already have, like eating a raspberry or a blueberry, helps determine where to put that new information in your memory.
When you consolidate a memory you are organizing it in a way that will be easier to recall. The third stage is storage, and it takes place throughout the cortex.
In storage, the information that gets linked up to existing memories get preserved or retained. Now in order to retain a memory, it has to be edited, pared down and simplified.
So less important details, like what you were wearing or what day of the week it was when you tasted the strawberry, get edited out.
That way the memory stays focused on the really important stuff the sweetness, size, color and texture of the strawberry - the stuff that matters.
The fourth stage is retrieval, and it occurs in the prefrontal cortex, hippocampus, and cortex. In retrieval, the brain goes through encoding, consolidation, and storage of the memory over and over again.
And with each run-through, retrieval gets easier. If you’ve ever tried to memorize facts for a test, you’ve gone through the process of retrieval.
and you probably know that the more you run through that information,the more likely you’ll be able to remember it on the test.
The retrieval stage protects memories from being lost - the oldest, most retrieved memories are most resilient. Now, with amnesia, any of these four stages can be affected.
Amnesia can be categorized into two types, according to which stages are impacted. The first type is anterograde amnesia and it refers to an inability to form new memories - often forgetting what happened hour to hour.
This can feel incredibly confusing and frustrating for individuals as they struggle to recall recent events like who they just spoke to or where they just came from.
Anterograde amnesia is usually because of a problem in the encoding or consolidating stage, and typically results from damage to the prefrontal cortex or hippocampus.
The second and probably most well-known type of amnesia is retrograde amnesia, and it refers to an inability to recall old memories.
This can cause anxiety for individuals with retrograde amnesia as well as friends and family as they completely forget important people or moments in their life.
Often, individuals might create false memories, called confabulations, or might have difficulty placing a specific memory in time.
Retrograde amnesia is usually because of a problem in the storage or retrieval stage, and typically results from damage to the cortex, but could involve the prefrontal cortex or hippocampus as well.
Both anterograde and retrograde amnesia can be caused by acute and chronic conditions. Acute causes include traumatic head wounds or infections.
And Chronic causes include brain tumors and neurodegenerative diseases, including dementia and alzheimer’s. Amnesia can also develop from a thiamine or vitamin B1 deficiency, and in that setting it’s called Wernicke-Korsakoff syndrome.
Amnesia can also result from medical procedures like electroconvulsive therapy, as well as medications like benzodiazepines.
Besides brain injury or illness, retrograde amnesia can result from psychological trauma, in which case it’s termed dissociative amnesia.
It’s unclear how psychological trauma causes retrograde amnesia, but it’s thought that perhaps forgetting traumatic events is a psychological defense against the distress they can cause.
Sometimes dissociative amnesia targets a specific memory, like a specific violent event, whereas other times it can be more general, wiping out whole decades of memories.
Sometimes dissociative amnesia is accompanied by dissociative fugue, where a person suddenly wanders away from their home or community without a clear memory of having done that.
Diagnosis of amnesia often requires getting a medical history from the person affected, as well as their friends and family to help fill in possible gaps.
Blood tests can detect nutritional deficiencies or infections that impact memory. And MRI or a CT imaging may be used to detect structural damage or abnormalities in the brain.
For a diagnosis of dissociative amnesia, the Diagnostic and Statistical Manual of Mental Disorders, or DSM-V, states that memory loss should “not occur exclusively during the course” of dissociative fugue, meaning that the memory loss should still be present after the episode of wandering away is over.
The DSM-V further states that the amnesia can’t be “due to any physiologic effects” of a drug, or be better explained by any other medical condition associated with retrograde amnesia.
In many cases, amnesia is temporary, and people will regain memory so long as the cause is addressed. Occupational and cognitive therapies can assist with the recovery process, by teaching people strategies for organizing and sorting new information, and help those with amnesia learn to manage day-to-day life.
Mobile phones and other portable digital devices have become an important part of treatment, as they can provide people with alarms and other reminders, as well as a way to store important information, like pictures and videos of close friends and family.
For dissociative amnesia, psychotherapy can help a person safely process traumatic memories. Alright, so as a quick recap, anterograde amnesia usually affects the encoding or consolidating stage of memory formation and causes a person to be unable to form new memories.
Retrograde amnesia usually affects the storage or retrieval stage of memory formation and causes a person to be unable to recall old memories.
One type of retrograde amnesia is a dissociative amnesia which is thought to be a psychological defense to dissociate or detach from distressing events in the past.