What Is… Memory and Amnesia

In this series, I dig a little deeper into the meaning of psychological terms. This week’s term is memory.

Memory is highly complex. There are multiple different types, as well as multiple areas of the brain that are involved. Memories not only need to be encoded in the first place, but they also need to be stored and then retrieved when needed in the future. Retrieval can involve either recognition (recognizing a stimulus when presented) or recall (spontaneously producing information). Recall may be easier in the same physical location where the learning occurred.

Types of memory

Explicit

Explicit memory, also known as declarative memory, is under conscious control and involves of factual information. It consists of semantic (general knowledge) and episodic (memories of events) memories. Episodic includes autobiographical (things related to the self), and flashbulb memories, which involve important events at a specific point in time.

Implicit

Implicit memory is what’s humming along behind the scenes. Procedural memory is one type of this, and it allows us to go on autopilot with routine tasks, like brushing our teeth. With priming, retrieval of task-associated memories speeds up after doing the task. Emotional learning, such as learning to fear a certain stimulus, is another form of implicit memory.

Short-term

Short-term memory is limited to around 18 seconds. Experiments have found that when recalling numbers, such as a ten-digit phone number, it is easier to remember numbers in chunks of 3+3+4 digits rather than trying to remember the 10 digits as a single unit. When trying to recall a phone number we may repeat it to ourselves over and over in order to hold it in working memory; this is referred to as a phonological loop.

Working memory holds material in the short term for processing and manipulation. Its capacity is correlated with complex cognitive task performance, including reading comprehension and problem-solving. Functioning tends to decline in advanced age.

Sensory memory is also short-term, and holds sensory details from the massive amount of stimuli picked up by our senses for a very brief time, around one second.

Long-term

Our long-term memory capacity is enormous. Sleep enhances encoding for long-term storage and allows neural connections to be strengthened.

Regions of the brain

Several different areas of the brain can be involved in managing particular types of memories. The prefrontal cortex and parietal lobe are involved in working memory, while the hippocampus is the major structure involved in creating long-term memories.

The amygdala is involved in emotional memory and plays a significant role in trauma memories.

Factors that can impair memory

Stress can interfere with working memory, the encoding of memories, and the functioning of the hippocampus. Intensely stressful events may be so intolerable to the mind that they are repressed from conscious awareness.

Effects of illness

There is a broad range of illnesses that can have a negative impact on memory. In Alzheimer’s Disease, protein plaques invade the brain. In traumatic brain injury, there may be physical damage to areas of the brain involved in the formation and retention of memories.

Bipolar disorder and major depressive disorder have both been associated with decreases in the size of the hippocampus. Abnormalities in the hippocampus have also been associated with PTSD and anxiety disorders.

Living with depression

I’ve definitely noticed that depression has an effect on my ability to remember. I do much better with recognition than I do with recall. Spontaneously trying to fish things out of the recesses of my mind can be problematic, but I know the information (at least some of it) is still in there, as it’ll sometimes pop up unannounced when I’m not looking for it. I’ve learned to make note of things quickly because I know my brain isn’t going to hold onto it very long.

Amnesia

Amnesia is a memory deficit that can go in two different directions. Retrograde amnesia goes backward, affecting previously stored memories. Anterograde memory loss goes forward, affecting the ability to move short-term memory information into new long-term stored memories.

There are multiple types of amnesia that can have retrograde or anterograde effects. Typically, the effect is on declarative rather than procedural memory.

Neurodegenerative diseases

Alzheimer’s disease and other forms of dementia are degenerative diseases that cause memory loss as a result of physical changes in the brain.

Brain injury

Post-traumatic amnesia occurs following a traumatic brain injury such as a concussion. While it lasts, new events can’t be stored in memory. The effects can be both retrograde and anterograde. The Galveston Orientation Amnesia Test (GOAT) is the most commonly used test for post-traumatic memory disruptions.

Transient amnesia

Transient global amnesia is a neurological disorder with attacks that last several hours and involve short-term memory being effectively knocked out, along with difficulties retrieving older memories. Aside from that, though, the person is cognitively intact. The cause isn’t understood, but it has been linked to migraines and epilepsy.

Dissociation

Dissociative amnesia can result from periods of dissociation, such as in dissociative identity disorder, or repressed memories. Memory loss may occur during traumatic situations like sexual assault. Some of the event memories may consolidate after a couple of nights’ sleep.

Korsakoff’s syndrome

Korsakoff’s syndrome can result from a severe deficiency in thiamine due to long-term alcoholism. People with this disorder tend to confabulate, meaning their brain unconsciously makes up stories to fill gaps in memory. This is not conscious lying; rather, it is an involuntary process.

Related to medical treatment

Drug-induced amnesia can be useful during medical or dental procedures to reduce memories of the procedure once it’s done. Colonoscopies and wisdom tooth removal are examples of procedures where amnestic drugs like the benzodiazepine midazolam may be used.

Electroconvulsive therapy (ECT) can potentially cause anterograde and retrograde memory loss.  I experienced both. The anterograde effects didn’t bother me all that much, and I didn’t tend to notice it as much as my family did, since they hadn’t forgotten that I’d already asked the same question 10 times. The retrograde effects were more disturbing. Some of those memories came back eventually, but others didn’t. It was a strange feeling, especially if I was looking at photographs of myself doing things I felt certain I’d never done.

Our remarkable brains

Between all of these potential causes for amnesia and the cognitive biases that tend to skew our thinking and memory, it really is quite amazing that our memories work as well as they do and as often as they do.

If you’re interested in learning more about memory, I recommend neuroscientist Lisa Genova’s book Remember; you can read my review here.

Is memory something that’s a problem for you? Do you have any tricks you use?

References

• Merck Manual Professional Version: Amnesias
• Wikipedia: Amnesia | Memory – Long-term, Short-term, Working | Post-traumatic amnesia | Transient global amnesia