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.
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/
