What Is… Memory and Amnesia

Types of memory explicit, implicit, short-term, long-term

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 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 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 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.


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 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.


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.

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?


The Psychology Corner: Insights into psychology and psychological tests

The Psychology Corner has an overview of terms covered in the What Is… series, along with a collection of scientifically validated psychological tests.

Ashley L. Peterson headshot

Ashley L. Peterson


Ashley is a former mental health nurse and pharmacist and the author of four books.

13 thoughts on “What Is… Memory and Amnesia”

  1. Very interesting subject matter. I noticed that when I was on certain medications in the past, my short-term memory was evident. I would talk to another and tell them about what happened during the day, and draw a complete blank mid-sentence. This really bothered me. I believe it was due to taking the seroquel at night. Sine not taking it, I’ve become a bitter sharper now.
    However… Long-term memory is something at times I wish I didn’t have. There are some memories I wish would leave and get out of my head.

  2. I notice my memory gets worser, as the stress gets worse. I have been a scatter brain since before Christmas with everything and the new things cropping up this month.

    I like my planner to be monthly visual base. I made my own diary this year so I could have a monthly planner that was large enough for my needs. I have been using this style for a couple a years, or more and found it works best for me.

    I like to use lists or little reminder notes for some things too.

  3. Memory is very hard for me at times..and can bring on quite embarrassing and then fearful responses. At the age of 46, I fear that I have early onset dementia at times because of my memory. I try to keep it together…and act ..by writing notes or putting things in my phones, so not to be completely blindsided. But there are times that (maybe due to stress) I have a hard time remembering things and it scares me. I will forget someone’s name and will not be “on,” which totally freaks me out.
    Very good article. What do I do? Just fake it…in hopes it will get better and no one will notice.

    1. Yeah, sometimes fake it til you make it is probably the best thing. And it’s so hard to know what is “normal” forgetfulness and what goes above and beyond that.

  4. I find this fascinating. Since my head injuries and the trauma I went through, others have identified major gaps in my memories. I don’t even know those memories are gone until it frustrates a friend or family member that those pages seem absent from my brain at the moment.
    Also I find that now, I need to write things down, otherwise I am inclined to forget the tasks I should be doing. I am glued to my diary and to-do lists for work.

      1. My family have noticed more gaps in memory than any additions of memories than never occurred.
        The odd thing is, I don’t know I don’t have a memory of a person or event, until it has caused others to be uncomfortable that I have not the foggiest who they are or what they are talking about.

  5. Trauma memories are not accessible consciously, they are considered implicit cit memory

    These memories can activate our fight or flight mechanism.

  6. Often I feel like my long term memory is pretty good, but my short term is shot. I feel like its been that way for years, so most of my vivid memories are from when I was much younger.

  7. I have a good memory for written data, but not things spoken. Sometimes I will forget a thing said to me within minutes, but if I read it I might remember it for years. I’ve always been this way. I take a lot of notes!

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