Are we able to control memory – and forgetting?

Keeping a Spotless Mind: The neuroscience of "motivated forgetting"

https://www.youtube.com/watch?v=NTQd--o61NQ

Prof. Michael Anderson

This is an interesting lecture by Prof. Michael Anderson who presents his case very clearly.

Prof. Anderson works at Cambridge University.  He believes that memory, like other aspects of cognition and behavior, is something we can control and as such it poses for us problems of control.  Anderson studies the mechanisms that allow us to suppress unwanted memories.  He studies the role of frontal systems of inhibitory control in forgetting processes.

Here are some of the interesting things he says in the:

Is forgetting good or bad?

Every one of us experiences frustration when he can't retrieve things that he is sure he knows, or when he can't remember a significant experience from his past about which he hears from someone else.

But there are many advantages to forgetting.  We tend to forget things that arise negative emotions like fear, shame and guilt.  We forget in order to be able to forgive – forgive ourselves for things we've done and are not proud of, and forgive others.  We forget things that threaten our self esteem.  Sometimes we forget our failings (or at least remember them vaguely, not in detail and not with the same emotional intensity).  This gives us strength to face similar situations and try again.

How do we forget?

The forgetting mechanism that Prof. Anderson suggests in this lecture is related to inhibitory control.  We know the term as part of executive functions.  Inhibition is the suppression of a strong and wrong response for a weak and correct one.  The more automatic a task is, the stronger the inhibition we will need to apply in order to stop it.  Prof.  Anderson gives an example of a cactus plant that falls off a table.  Our automatic reaction is to catch it, but there could be uncomfortable consequences…  The preferred and weak response would be to refrain from catching it and to clean the floor later (cautiously).

This is an example of an inhibition of a motor response.  Anderson argues that inhibitory control also helps us to control memory - to control what we retrieve from memory.

  

Sometimes we see or hear a stimulus that automatically invokes a specific memory.  But we don't always allow that memory to reach consciousness.  Sometimes the memory is irrelevant for our purpose at that moment, and sometimes it is emotionally difficult.  We can stop such memories and not experience them.  How?

In order to study this Anderson and his friends used a simple model of learning word pairs.  Participants in the study learned random word pairs like "picture – scissors"; "handle – flower"; "chimney – dog".  Then they were presented with the first word of each pair, and had to respond with the second word. 

In the second phase of the experiment the researchers divided the word pairs into three groups.

The first word of each pair in the first group was presented in green.  The participants responded with the second word– just like in the first phase of the study.  For example, they saw the word "picture" and responded with "scissors".

The first word of each pair in the second group was presented in red.  The participants were instructed that when they see a red word, they should stop their thoughts about that word's pair and not let it reach consciousness.  For example, they saw the word "handle" and were asked not to think about its pair.

The word pairs of the third group were not presented in this stage at all.

The third phase was a repetition of the first phase.  They presented the first word of each pair of all three groups, and asked the participants to say the second word. 

The green word pairs (like "picture – scissors") were recalled best.  These were trained in both phase one and two.  The word pairs that were not presented in the second phase at all (like "chimney – dog") were less well recalled.  The red word pairs that participants were asked to suppress (not to allow the second word to reach consciousness,  like the pair "handle – flower") were the least well recalled.

This means that we can intentionally forget when we try not to let certain information enter consciousness.  Anderson calls this Suppression Induced Forgetting.

Not all the stimuli we encounter, that can provoke a specific memory, would actually provoke that memory or strengthen it.  It depends on our inner stance or attitude towards that memory.  If we don't want to remember, these stimuli may actually help us to suppress that memory. 

Anderson and his friends found out, that when people suppress memories actively (like when they look at a red word and are asked not to think about its pair), there is a significant inhibition in the activity of the hippocampus in both sides of the brain!  The hippocampus is one of the brain structures that are the most important for memory.  The degree to which the hippocampus is suppressed when people look at a "red" word predicts the degree of forgetting of that word's pair in the third phase of the experiment.

Are we able to inhibit only specific unwanted memories, or is the inhibition more global, also affecting wanted memories?

Apparently, inhibition tends to be global.  Anderson argues that when we suppress an unwanted memory, it is accompanied by an "amnestic shadow".  When we encounter a stimulus that raises an unwanted memory, we suppress not only this specific memory, but also other completely neutral events, that are unrelated to that memory, that happened before and after we encountered that arousing stimulus. 

And thus stimuli that arise unwanted memories can interrupt learning of completely different, neutral things.

And so, following trauma there sometimes is a period of memory loss, even for things that are unrelated to the trauma.  In the past people thought it is related to stress, distractedness and sleep loss.  Anderson adds a fourth cause – suppression of the memory of the traumatic event that also affects other memories.

Not all of us can control memories or inhibit unwanted memories.  Children younger than 10-12, old people, people with anxiety and depression, ADHD, PTSD and brain injury have more difficulty doing it. 

Overgeneral autobiographical memory and its relation to depression and trauma

Williams, J. M. G., Barnhofer, T., Crane, C., Hermans, D., Raes, F., Watkins, E., & Dalgleish, T. (2007). Autobiographical Memory Specificity and Emotional Disorder. Psychological Bulletin, 133(1), 122-148.‏  http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.721.1249&rep=rep1&type=pdf

What is OGM – overgeneral autobiographical memory?

When certain people are asked to retrieve specific autobiographical memories (memories of specific events that happened at a specific time and place) related to key words, they tend to retrieve categorical, overgeneral memories – memories that group similar events together (for example, "I used to walk the dog every morning") instead of specific memories.

This phenomenon was first found by researchers Willians and Broadbent (1986) in suicidal patients.  Later it was found as a consistent characteristic of patients with a diagnosis of depression, postnatal depression and people with sub clinical levels of depression.  The phenomenon is also found in people with a tendency for rumination (passive and repetitive thinking about the depressive symptoms, and the possible causes and consequences of these symptoms.  For example, "What did I do wrong?" "Why am I not getting over this?").  Memory remains overgeneral in those with a history of emotional disorder, even if not currently in an episode.

The phenomenon of overgeneral autobiographical memory is also found in people with a history of trauma, like sexual abuse, physical abuse, traffic accidents, war trauma, cancer diagnosis etc.  OGM is found in these people even when they are not asked to retrieve memories related to their trauma, but rather memories that are related to certain key words.  OGM doesn't occur in every person who has gone through trauma.  It tends to occur more in people who reacted with post traumatic stress disorder and in people who experienced trauma in childhood.

The OGM phenomenon was assessed mainly by various versions of the AMT – autobiographical memory test.  This test usually uses emotional key words, for instance "excited", "happy", "relaxed ", "bored", "helpless", "lonely" and so on.  The person is asked to retrieve a specific event (that occurred at a specific time and place, lasting no more than one day) that is related to this key word. 

People with depression or post trauma tend to have OGM in response to both positive and negative key words.  People with depression or post trauma tend to respond with OGM even when the stimuli are not key words but situations (for example, " Recall a time when a neighbour helped you with a practical problem"), a general instruction ("Recall as many episodes from your life as you can in ten minutes") or actions ("Try to recall going to a concert").

How do researchers explain OGM?

There are three kinds of explanations:  Functional Avoidance, "capture" and executive dysfunction.

Functional Avoidance

The explanation is related to the structure of autobiographical memory.  According to Conway – Pleydell- Pearce model (2000), autobiographical memory has three hierarchical levels:

The highest level is the level of representations of life periods with clear beginning and end points (for example, being in high school, military service, the time when I lived in Tel Aviv etc.). 

The middle level has general event descriptions:  event that repeat themselves (for example, driving to work each morning) or singular events (for example, my vacation in South Korea).  The events are represented at this level as conceptualized and abstract summaries of experiences.

The lowest level has specific event knowledge.  In this level concrete, sensory and perceptual aspects of events are represented.  They can take the form of visual, auditory, tactile or other images of the event – what the surrounding looked like, who was present at the event, how I felt during the event etc.

When people receive a key word and are asked to recall a specific event related to this word, they create associations for the word that become the basis for memory search.  For example, for the word "calm" I can think about "my dog Jane".  Now people access the level of representation of life periods ("when I lived in Tel Aviv") or the level of general events ("I used to take her for walks") and from here they go on to the specific event level ("one day we went on a walk to "Ben Shemen" forest and she was frightened by a wild boar that suddenly appeared on the path"). 

For post traumatic people, this kind of memory search may lead to emotionally difficult places.  Consider the following protocol from a patient in response to the cue summer. She was thinking back of summer holidays and found “hot summer evenings” coming to mind. Further specifying on this theme, she began to retrieve a specific summer evening when, although already after 10:00 p.m., the temperature was still agreeable, and she was sitting outside with friends talking about the new puppy she had bought. Subsequently, however, this triggered another memory from that same summer when she was assaulted when walking the dog in the neighborhood park.

As a result of these kinds of experiences people with PTSD and people with depression tend to avoid memories which are too specific,  Conway and Pleydell – Pearce  argue that these people stop their search in memory at the level of general event description and tend to avoid reaching the level of specific events.

Capture

Individuals suffering from depression and people with a tendency for rumination may get "caught at the middle level (the general event level).  When such people receive, for example, the key word "happy", they may ruminate:  "why can't I be more happy?"  These thoughts "capture" them and prevent them from retrieving specific events from autobiographical memory.  These people move across the middle level of autobiographical memory instead of moving downward towards the more specific level.

Executive functions

Searching in memory according to a cue requires effort, strategy, control and monitoring – that is, executive functions.  During the search a person has to inhibit irrelevant autobiographical knowledge (and also ruminative thoughts that disturb the search for a specific event). 

People with depression and post trauma have depleted attention resources and executive control.  Their difficulties are especially salient in the aspects of initiating and managing the search and inhibiting irrelevant information during the search.

Thus, functional avoidance, "capture" at the middle level of autobiographical memory and poor executive functions cause the overgeneral memory phenomenon.  These factors also work together and interact and thus exacerbate the problem. 

Overgeneral autobiographical memory may lead to slow recovery from depression or traumatic events.  OGM may also lead to difficulties in problem solving, because OGM makes it harder for us to lean on past experience when we deal with new situations.

Fortunately, training people with depression or PTSD to retrieve specific memories can lead to improved emotional state and can prevent the development of another episode of depression.  This can be done, for example, by creating a list of specific memories that the patient wants to remember.  Each item on the list is linked via visual imagery to a specific location on a "mental trail".  The person takes a mental hike and retrieves the memories along the trail.  This technique prevents the development of depression.

Another way is to train depressed people to focus on concrete images which are not self centered and have aspects of perceptual processing/mental imagery (“Think about the face of the Mona Lisa,” “a raindrop falling down a window pane”).  This leads to retrieval of much more specific autobiographical memories.  Retrieval of specific memories alleviates depression.

One of the authors of this paper, Dalgleish, elaborates on this subject in this interview:

https://www.youtube.com/watch?v=SOHshGw8WS0

Clinical depression and memory: Professor Tim Dalgleish

Is episodic memory a (narrow) cognitive ability? Part three: Individual differences in episodic memory – the case of especially poor episodic memory

 .

Can episodic memory be a (narrow) cognitive ability?  It has to fulfill a number of conditions for that.  In the first post of this series we've seen that episodic memory develops through the lifetime.  In the second post we've began to look into individual differences in episodic memory.  We've discussed people with especially high episodic memory.

In this post we'll discuss a group of people with an especially poor episodic memory. 

First, a quick reminder of concepts (you can skip to the green color below):

Episodic memory is memory for life events that we'd experienced in a specific place at a specific time.  The hallmark of episodic memory is the experience of mentally "being there".

 Autobiographical memory is composed of episodic memory and semantic knowledge about ourselves and about things that took place in the world during our lifetimes. Semantic knowledge about the self is, for example, knowledge about our character and hobbies and about places we've been to, in a way that is not necessarily tied with specific episodic memories (I know I'd visited a specific place and know what it looks like, but don't remember the experience itself).

Semantic memory is the fund of knowledge we've accumulated over the years (facts, ideas, word and concept meanings, knowledge about our culture).

In 2004 a woman named Susan McKinnon read a paper about psychologist Endel Tulving, that drew the distinction between semantic and episodic memory.  The paper presented a case of a man whose episodic memory was negatively affected as a result of brain damage following a car accident. McKinnon realized that that man's symptoms resemble her experiences (minus the brain damage).

Tulving expressed his belief that there are intelligent and completely healthy people with no ability to remember personal experiences.  These people have poor episodic memory.  Tulving thought that soon these people will be discovered.  McKinnon realized Tulving is referring to people like her. 

McKinnon is healthy, she is married and has a family.  She is now retired and in the past has worked as a professional.  She doesn't remember any events of her life.  She doesn't remember good and exciting events, arguments or traumatic events.  She knows about the existence of these events but has no experience of them.  She doesn't remember books she'd read or movies or TV series she'd watched.  Her ability to form mental images is not very good.

In 2006 McKinnon decided to approached Dr. Brian Levine who worked with Tulving.  Levine tested her and she became the first person to be diagnosed with SDAM – severely deficient autobiographical memory.  Later Levine found two more people with a similar autobiographical memory, and in 2015 published with his colleagues Palombo, Alain, Söderlund & Khuu a paper about SDAM.  Since the paper's publication, hundreds of people approached Dr Levine thinking they too have SDAM.  Levin's group now tests these people.  Levine assumes he'll find less than 15 people with SDAM in this group.

The three people with SDAM are intelligent people (their IQs are above 110), they are all well educated (one of them has a Phd.) and they all work. Their poor autobiographical memory does not affect their everyday functioning.  These people are healthy, they do not suffer head injuries, neurological diseases or psychological trauma.  Two of them have had a single episode of depression many years ago, when they were adolescents.  Two out of three are in long term relationships and one is single.

All of them realized they have poor autobiographical memory during late adolescence or early adulthood. 

The researchers compared them with 15 people similar in age (47 on average) and education (16.5 years of education on average). 

Of the cognitive tests, the only measure all three were poor at was recall of the RCFT figure.      

The authors think that visual recall is inherent to autobiographical remembering.  That is, when we recall a past event we create a visual image of it.  They cite another study in which two healthy people with a total inability to form visual imagery throughout their lives had poor ability to relive episodic events.  One of them, who by chance had neuropsychological testing in the past, had poor visual memory, and poor RCFT performance. 

How was autobiographical memory assessed in this study?

Each person of the SDAM and the control group chose two events from each of six life periods:  a week ago, a month ago, a year ago, ten years ago, during adolescence and in childhood. Each of these events had to have happened at a specific time and place.  The people could look at almanacs or ask people close to them to name such events (for instance, "on July 2016 you've visited Seorak Park in South Korea").  The consulted people were asked not to add any details about the event.

Each person of the SDAM and the control group elaborated about these events to the best of his ability.  The researchers analyzed the stories and classified the details to be episodic (directly related to the main event, specific to time and space, creates a feeling of re-experience) or semantic/"external" (for example, facts about Korea of about other places in Korea which are not necessarily related to the same visit). 

The researchers found that the people with SDAM produced much less episodic details relative to the control group – but only for events that happened during youth and adolescence. 

The number of episodic details that the three people with SDAM could tell about events in later lifetimes was not significantly different than that of the control group.  This was so despite the fact that SDAM people said they don't have an experience of these events.  How could this be?

The researchers assume that SDAM people could provide episodic-like details as a result of activating non episodic processes (semantic processes).  SDAM people are used to make up for the lack of personal experience by becoming familiar with the story of the event.  The story of the event is retold each time the event is mentioned, and people who were present when the event took place have a chance to add details to the retelling.  Pictures from the event also enrich the story.  I'll also hypothesize that events from the remote past are less often spontaneously mentioned, and are mentioned less in the company of people who took part in them and can enrich the story.

Apparently it's hard to distinguish between episodic details and episodic-like details.  Often "rememberer" himself has difficulty distinguishing between them.  Each time we tell an episodic event we combine episodic details and episodic-like details.  I'm not sure that we can distinguish between small details that we remember directly from an event that occurred many years ago, and small details that someone else who was present in the event added to the event's story.  During remembering we are also assisted, without being aware of it, by a "script" or a "schema" according to which such an event is supposed to happen.

This emphasizes the extent to which autobiographical memory is a phenomenon that is in between the personal and the interpersonal/social.  Autobiographical memory is to some extent a story with a number of authors, a story that is influenced by values and norms of the culture we live in.

In order to overcome such issues the authors let judges who were blind to the person's group affiliation have a qualitative impression of the memory.  The judges did get the impression that the memory quality of the three SDAM people for events that occurred not only during childhood and adolescence, but also ten years or one year or one week before was poorer (in terms of the richness of the memory and the extent of reference to events that happened before and after the main event) than the memory quality of the control group.

Neurologically, the three SDAM people had smaller right hippocampuses than the control group.  During recall of episodic events under fMRI, SDAM people had less activity in brain areas related to autobiographical memory and visual memory.

To sum up, we've seen evidence for the possible existence of a group of people who can't remember events from their lives, who have no episodic memory.  These are healthy, educated working people that are highly functioning cognitively and interpersonally.  Due to the small size of the group it's hard to tell whether their poor visual memory characterizes other people with SDAM.  Generally, it's hard to come to any conclusions on the basis of a group of three people.  A larger study is being currently conducted.

These findings are thought provoking.  We are used to think about our life story as an essential part of our selves, and of autobiographical memory as an essential part of our selves.  But these people definitely have a self concept, personality, hobbies, values, beliefs, opinions and friends.  They know who they are.

Furthermore: the ability of these people to function so well in everyday life in all respects – professionally, personally – raise the question: to what extent is episodic memory essential? And if it's not essential – why did it develop?

       

Palombo, D. J., Alain, C., Söderlund, H., Khuu, W., & Levine, B. (2015). Severely deficient autobiographical memory (SDAM) in healthy adults: A new mnemonic syndrome. Neuropsychologia, 72, 105-118.‏ http://www.sciencedirect.com/science/article/pii/S002839321500158X

The strange case of the woman who couldn't remember her past – and can't imagine her future.  Erika Hayasaki.  WIRED.

https://www.wired.com/?p=1994722

Can episodic memory be a (narrow) cognitive ability? part two: Highly Superior Autobiographical Memory

Can episodic memory be a (narrow) cognitive ability?  Only If it fulfills a number of conditions.  We've discussed one of them in the previous post.  We've seen that episodic memory develops through the lifespan.

Are there individual differences in episodic memory?  Do people in the same age group differ in their episodic memories?   Apparently so.

In this post we'll discuss people with an especially strong and rich episodic memory. 

Episodic memory is memory for life events that we'd experienced in a specific place at a specific time.  Autobiographical memory is composed of episodic memory and semantic knowledge about ourselves and about things that took place in the world during our lifetimes.  Semantic self knowledge is, for example, knowledge about our character and hobbies and about places we've visited, in a way that is not necessarily tied with specific episodic memories (It's possible for me to know I've been to a specific place and to know what it looks like, without recalling the visit itself).

Semantic memory is the fund of knowledge that we've accumulated (facts, ideas, meanings of words and concepts, knowledge about our culture).

In CHC terms the broad ability "Comprehension Knowledge" is the content of our  memory.  The broad ability "Long Term Storage and Retrieval" is the process of storing this content in memory and retrieving it from memory.

In 2000 Prof. McGaugh, a neuropsychologist at California University, received an intriguing email.  The writer was a 34 year old woman who wrote: "…since I was eleven I have had this unbelievable ability to recall my past, but not just recollections… I can take a date, between 1974 and today, and tell you what day it falls on, what I was doing that day and if anything of great importance (i.e.: The Challenger Explosion, Tuesday, January 28, 1986) occurred on that day I can describe that to you as well. I do not look at calendars beforehand and I do not read twenty-four years of my journals either. Whenever I see a date flash on the television (or anywhere else for that matter) I automatically go back to that day and remember where I was, what I was doing, what day it fell on and on and on and on and on. It is non-stop, uncontrollable and totally exhausting. Some people call me the human calendar while others run out of the room in complete fear but the one reaction I get from everyone who eventually finds out about this “gift” is total amazement. Then they start throwing dates at me to try to stump me… . I haven’t been stumped yet. Most have called it a gift but I call it a burden. I run my entire life through my head every day and it drives me crazy!!!…"

Prof. McGaugh and his staff were very skeptical about the woman's description, but nevertheless they invited her for a meeting.  This meeting led to five years of numerous tests and interviews.  Very early on Prof. McGaugh and his colleagues realized that her memory was different than other cases of good memories reported in literature.  She wasn't good at storing and retrieving long lists of words, for example.  Her memories were very personal.  They were related to things that interested her and to dates from the period of her lifetime.

The researchers validated her autobiographical memory with events she wrote in her personal diaries which she kept since the age of 10 and with events her mother told them.  As for events in the public domain ("The Challenger Explosion") – the researchers could validate the dates, the day of the week on which they happened and details of these events with external data sources.

The researchers were amazed to learn how extraordinary this woman's memory is.  They published her case in a paper in 2006.

A short time after the publication, her story raised a huge interest in the media.  At first she kept her identity secret, but later she decided to come out with her full name – Jill Price. 

Following the publication six more people with this kind of memory were discovered, leading to this 60minutes episode.

Gradually more cases were discovered and this phenomenon was named HSAM – Highly Superior Autobiographical Memory.   By now there are about 50 people in the world known to have HASM, and they seem to have similar characteristics:

a.  Memory organized by dates.  These people can retrieve episodic memories for specific dates in specific years.  They know what day of the week a specific date fell on.   When given a public event that occurred when they were 10 or older, they can say the exact date on which this event happened.  The event does not have to be very salient, but it has to be one that interested them (even a specific episode of a television series).   

b.  When people with HSAM retrieve an episode that took place many years ago, they relive it emotionally as they have when it actually happened.   Joey DeGrandis who has HSAM says:  "For a given date, I could probably tell you something that happened to me on that day, where I was in life, and the emotions attached to that. When I’m recalling these memories I’m really back there, emotionally. I’ll remember how I was feeling at a certain time very vividly...  The memory will trigger images, sentiments, emotions—literally the way someone looked in a certain light or something like that."

C.  Higher than average blending of semantic and episodic memory.  People with HSAM not only have a rich autobiographical memory but also a wide repertoire of information about events that took place in the public domain (all related to the dates they took place on).  Information in the public domain is usually maintained in semantic memory in a decontextualized form.  For instance, I don't remember where I was or what I was doing when I first encountered the term "political correctness".  Obviously there was an event during which I learned about this phrase, but it now exists in my semantic knowledge without the context during which I acquired it.

Only events in the public domain that are very unusual are coded in our memory with their episodic context.  Everybody probably remembers where he was and what he was doing when he learned about 9/11.  It seems to me that the powerful emotional reaction this event raised made the context inseparable from the semantic knowledge about the event.

I guess by what Joey DeGrandis and others have said, that maybe people with HSAM attach powerful emotional reactions to everyday events, which causes their storage in memory with their context.  This makes semantic memory more organized and facilitates retrieval.  People with HSAM have fuzzy boundaries between semantic and episodic memory.

d.  OCD features.  It seems that people with HSAM have OCD-like features.  For instance some of them keep their things in a specific order.  It's unclear whether the superiorly organized autobiographical memory developed as a coping style with anxiety or the OCD tendencies developed as a way to deal with the flood of autobiographical memories, some of them unpleasant.  There could also simply be a correlation between HSAM symptoms and OCD.  There is a resemblance between the brains of people with HSAM and the brains of people with OCD.  Both have enlarged caudate and putamen.

e.  Maintenance.  People with HSAM tend to activate their autobiographical memory when they rest or daydream, in ways that can be conducive to its organization and maintenance.  For example, they recall all dates on which they had dinner at specific restaurant and what happened on each visit.  Or, they recall what happened on a specific day a year ago, two years ago, three years ago and so on.  Or they try to recall as many dates of a specific year as they can.  Some keep a personal diary.  Some researchers see these maintenance habits also as OCD-like features.

f.  Neurological findings.  people with HSAM have morphological changes in nine brain structures as compared to a control group.  Among these areas are, as mentioned above, enlargements of the caudate and the putamen.

g.   Many of the first people with HSAM had difficulty with relationships.  One of the hypotheses about this is that they clearly remember conflicts with their partners, which makes it harder for them to forgive and carry on.

To summarize, we asked whether episodic memory can be a narrow cognitive ability.  In order to be a narrow cognitive ability it has to fulfill a number of criteria.  One of them is interpersonal differences.  In this post we talked about people at one end of the spectrum – people with HSAM – highly superior autobiographical memory.

Parker, E. S., Cahill, L., & McGaugh, J. L. (2006). A case of unusual autobiographical remembering. Neurocase, 12(1), 35-49.‏ http://www.psych.ufl.edu/~fischler/Hm/Parker06_MemorySavant.pdf

LePort, A. K., Mattfeld, A. T., Dickinson-Anson, H., Fallon, J. H., Stark, C. E., Kruggel, F., ... & McGaugh, J. L. (2012). Behavioral and neuroanatomical investigation of highly superior autobiographical memory (HSAM). Neurobiology of learning and memory, 98(1), 78-92. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3764458/

LePort, A. K., Stark, S. M., McGaugh, J. L., & Stark, C. E. (2015).Highly superior autobiographical memory: Quality and quantity of retention over time.Frontiers in psychology, 6.‏ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4720782/