Posts Tagged ‘episodic memory’

Brain Regions Associated with Long-Term Memory

September 11, 2019

This post is based on an important book by Scott D. Slotnick titled “Cognitive Neuroscience of Memory.” Remember to consult the website http://www.brainfacts.org/
to see the anatomical information referred to in this post.

Dr. Slotnick writes, The term episodic memory can refer to many other related forms of memory including context memory, source memory, “remembering,” recollection, and autobiographical memory, which refers to a specific type of episodic memory for detailed personal events. As the names imply context memory and source memory refer to the context in which something occurred and source memory refers to where the event occurred.

Episodic memories are related to activity in both control regions and sensory regions of the brain. Sensory cortical activity reflects the contents of memory. The control regions that mediate episodic memory include the medial temporal lobe, the dorsolateral prefrontal cortex, and the parietal cortex. There are many regions associated with episodic memory but the primary regions are the medial temporal lobe, the dorsolateral prefrontal cortex, and the parietal cortex. The parahippocampal cortex processes the context of previously presented information such as the location or the color.

The hippocampus binds item information and context information to create a detailed episodic memory. Dr. Slotnick provides the following example. “If an individual went on a vacation to Newport Beach in California and later recalled meeting a friend on the beach, that individual’s perirhinal cortex would process item information (the friend), the parahippocampal cortex would process context information (the area of the beach on which they were standing), and the hippocampus would bind this information and context information into unified memory.”

Semantic memory refers to knowledge of facts that are learned through repeated exposure over a long period of time. These facts are processed and organized in semantic memory, which provides the basis for much thought. Subjectively, semantic memory is associated with “knowing.” Semantic memory includes definitions and conceptual knowledge, and this cognitive process is linked to the field of language.

Semantic memory has been associated with the left dorsolateral prefrontal cortex (in a different region associated with episodic memory), the anterior temporal lobes, and sensory cortical regions. The left dorsolateral prefrontal cortex may reflect the processing of selecting a semantic memory that is stored in other cortical memories. For example, naming animals activates more lateral inferior occipital-temporal cortex that has been associated with the perception of living things, while naming tools activates more medial inferior occipital-cortex that has been associated with perception of nonliving things.

In a study of Alzheimer’s patients, the impairment in an object naming task, which depends on intact semantic memory, was more highly correlated with cortical thinning in the left anterior temporal lobe. This finding suggests that the left anterior temporal lobe is necessary for semantic memory.

During long-term memory the hippocampus binds information between different cortical regions. But long-term memory may only depend on the hippocampus for a limited time. In the standard model of memory consolidation, a long-term memory representation changes from being based on hippocampal-cortical interactions to being based on cortical-cortical interaction, which takes a period of somewhere between 1 to 10 years. A person with hippocampal damage due to a temporary lack of oxygen might have impaired long-term memory for approximately 1 year before the time of damage from retrograde amnesia and have intact long-term memories for earlier events. This suggests that the hippocampus is involved in long-term memory retrieval for approximately 1year as more remote long-term memories no longer demand on the hippocampus so they are not disrupted.

The activity in the hippocampus did not drop to zero for older semantic memories but was well above baseline for events that were 30 years old. This indicates that the hippocampus was involved in memory retrieval for this entire period. If the hippocampus was no longer involved, the magnitude of activity in this regions would have dropped to zero for remote memories.

There is a growing body of evidence that the hippocampus is involved in long-term memories throughout the lifetime. As such, the process of consolidation does not appear to result in the complete transfer from hippocampus-cortical memory representation to cortical-cortical memory representations.

Cognitive Neuroscience of Memory

September 6, 2019

The title of this post is the same as the title of an important book by Scott D. Slotnick. He writes in the preface, “The human brain and memory are two of the most complex and fascinating systems in existence. Within the last two decades, the cognitive neuroscience of memory has begun to thrive with the advent of techniques that can non-invasively measure human brain activity with spatial resolution and high temporal resolution.

Cognitive neuroscience had not been created when HM was a graduate student. The field is quite new. In cognitive psychology we studied cognitive processes, of which memory was central, but little was known about the neuroscience underlying memory.

Before getting into neuroscience it is important to understand what memory encompasses. Most people think of memory as something they need to use to pass exams, are frustrated by exam failures, and by an inability to remember names. Readers should be aware of the function of memory. Memory is a tool for time travel. We use it to help us predict and deal with the future. The more we learn, the more we have information for dealing with the future. Moreover, there are many types of memory.

The first pair of memory types is explicit memory and implicit memory. These refer to conscious memory and nonconscious memory. They differ in that all forms of explicit memory are associated with conscious experience/awareness of previously experienced memory, whereas all forms of implicit memory are associated with a lack of conscious experience/awareness of the previously experienced information.

Skills are one type of implicit of memory. After a skill is learned, performance of that skill reflects nonconscious memory. Once a person has learned to ride a bike, she doesn’t think about rotating the pedals, steering, breaking, or balancing. Rather, their conscious experience is dominated by where she wants to ride or whatever else she happens to be thinking about. Repetition priming is another type of implicit memory that refers to more efficient or fluent processing of an item when it is repeated. When a television commercial is repeated, that information is processed more efficiently (and when the item from the commercial is seen again while shopping, implicit memory presumably increases the chance that it will be purchased.) Skill learning can be assumed to be based on repetition priming.

The remaining memory types are types of explicit memory. A second pair of memory types is long-term memory and working memory. Working-memory is often referred to as short-term memory. A recognition memory experiment will be described to help make the distinction between long-term memory and working memory. During the study phase of both long-term memory and working memory, items such as words or objects are presented. After the study phase, there is a delay period that will last as a function of specific amount(s) of time. During the test phase, old items from the study phase and new items are presented, and participants make “old” or “new” judgments for each item. This is termed old-new recognition. A greater proportion of “old” responses to old items than “old” responses to new items indicates the degree of accuracy of the memories.

Long-term memory and working memory differ with regard to whether or not information is kept in mind during the delay period. Typically there are many items in the study phase and the delay period is relatively long (typically minutes to hours). Obviously participants do not actively maintain information from the study phase during the delay period. In working memory experiments, there are typically a few items in the study phase, the delay period is in seconds and participants are instructed to actively maintain information from the study phase in their mind.

Another pair of memory types is episodic memory and semantic memory. Episodic memory consists of the memories we have of our experiences. Semantic memory refers to retrieval of, hopefully, factual memory that is learned over periods of time such as the definition of a word. Unfortunately, semantic memory also consists of misinformation and erroneous beliefs. And, unfortunately, this misinformation and erroneous beliefs can be further amplified via technology and social media.

Another pair of memory types is “remembering” and “knowing.” “Remembering” refers to the subjective mental experience of retrieving details from the previous experience, such as someone retrieving where they parked their car in a parking lot. If any details are recalled from a previous experience, this constitutes “remembering.” “Knowing” is defined by the lack of memory for details from a pervious experience, such as when someone is confident they have seen someone before but not where or when they saw them. Remembering is usually assumed to be related to context memory, as it is thought to occur whenever contextual information is retrieved. “Knowing” is typically assumed to be related to item memory and semantic memory. The last pair of memory types is recollection and familiarity. The terms recollection and familiarity can refer to mathematical models of these two kinds of memory, but more commonly refer to all the forms of detailed memory (episodic memory, context memory and “remembering”) and non-detailed memory (semantic memory, item memory, and knowing). Dr. Slotnick writes, “It may be useful to think of context memory and item memory as measures of task performance, “remembering” and “knowing” as measures of subjective experience, and recollection and familiarity as general terms that describe strong memory and weak memory, respectively.”

31st Meeting of the Association for Psychological Science Pt. 2

June 3, 2019

A definite highlight of the meeting was lecture by Lynn Nadel titled, Taking James Seriously: The Implications of Multiple Memory Systems. The James referred to in the title is William James, the father of American Psychology. James wrote about multiple memory systems, a primary and a secondary memory, which today are referred to as short term and long term memory. He made a distinction between habits and memory.

James passed away long before the emergence of neuroscience. The hippocampus plays an important role in the processing of memories. There was a famous epileptic patient referred to as HM who had large portions of his temporal lobes removed. A hippocampus is located in each one of those lobes. Although his previous memories remained intact, not only each new day, but each new hour was a new experience for HM. And these experiences would not be remembered.

There is a distinction between episodic memory, which holds the memories of our daily experiences is processed in the hippocampus, and semantic memory, which holds our general knowledge of the world, is resident in our neocortex.

The hippocampus is also critical to navigation. The neuroscientist O’Keefe identified place cells in the hippocampus. These place cells identify spatial locations where the organism travels. Learning to navigate entails strengthening these place cells and learning to follow them to desired locations.

In most species, the hippocampus matures postnatally. This has important consequences for memory and cognitive development. Dr. Nadel asks what does it mean to start life with a developing, but not yet functioning hippocampus, perhaps uniquely susceptible to impacts of experience early in life. In humans it takes 18-24 months for the hippocampus to emerge, and it takes 10-12 years for it to become fully functional.

Dr. Nadel speculates that phobias can develop before the hippocampus emerges. This late emergence of the hippocampus explains infantile amnesia and delayed exploration and place learning. Everything we learn very early in life is context free. The individual has no understanding of why she has certain fears, as the cause of the fear was not stored in memory. As for the 10-12 years for the hippocampus, an extremely important structure, to become fully functional, it might result in shortcomings in learning and interpersonal interactions.

The Hippocampus

May 18, 2017

The hippocampus receives considerable attention in “The Truth About Language” by Michael C. Corvallis.  As the hippocampus plays a critical role in memory, it is not surprising that it is central to language and time travel.  As we each have a hippocampus in each hemisphere of the brain, we have two hippocampi.

The importance of the hippocampus was first realized when an Englishman underwent surgery for epilepsy, and the surgery destroyed major parts of both hippocampi.  After this surgery he could no longer form new episodic memories.  Episodic memory involves memories having to do with the specific episodes of our lives.   Although his semantic memory, his general knowledge, remained intact.  Not only was he unable to recall the past, he was also incapable of imagining the future.

In the final years of my Mom’s life she suffered from dementia.  When I visited her, she was always glad to see me.  However, if an attendant took her to the restroom while I was visiting, when she returned she acted as if I had just arrived.  That is, she had stored no memory of my being there.

The hippocampus is the hub of the brain circuit involved in episodic memory and mental time travel.  Brain imaging shows it to be activated both when people remember past events and when they imagine possible future events.  It is also activated when people are asked to imagine purely fictitious  episodes.   Although other brain regions are involved, reflecting the fact that memory and imagination involve information stored in widely dispersed areas, the hippocampus appears to be the most critical component in that damage to it has the most debilitating effect on the ability to mentally escape the present.

The default-mode network, responsible for our mind wandering, is identifiable in primates and even in rats.  The hippocampus plays a critical role in both rat and human memory.  Recording from the hippocampus of the rat reveals that single neurons code where the animal is located in the spatial environment.  These neurons serve as place cells and together generate what has been termed a cognitive map of the environment that tells the rat where it is.  It plays the same role in humans.  Studies have shown that the hippocampus  is enlarged in licensed taxi drivers in London, who are required to memorize the map of London for their licenses.

Research using rats has indicated a similar competence.  In an experiment rats were trained to alternate left and right turns at a particular location in the maze.  Between trials they were introduced to a running wheel and, while they were running, activity in their hippocampi was recorded.  This activity coded which way the rats planned to turn in the maze on the next trial.  Apparently these rats were planning ahead for their next try at the maze.  The researchers also noted that autonomous activity in the hippocampus involved the computation of distances, and also supported the episodic recall of events and the planning of action sequences and goals.  One researcher wrote that “replay in the rat hippocampus can either lead or follow the behavior once the map of space is established.  This suggests that replay phenomena may support ‘mental time travel’ through the spatial map, both forward and backward in time.

Research on human patients about to undergo surgery had electrodes placed in cells in the medial temporal lobe, in an attempt to locate the source of epileptic seizures.  They were then asked to navigate a virtual town on a computer screen and to deliver items to one of the stores in the town.  Then were asked to recall only the items and not the location to which they were delivered.  However, the act of recall activated the place cells corresponding to that location, effectively mirroring the replay of place cells in the rat brain.

In another study, people were shown sequences of four videos of different events.  At one level. narratives were linked to each video, encouraging attention to individual details. At the next level, narratives linked a par of videos, and at the final level a narrative linked all four videos.  As the people processed these narratives, activation in the hippocampus progressed from the rearward end to the forward end as the scale of the narrative shifted from small and detailed to larger and more global.    Dr. Corvallis notes that this probably happens when we read novels.  Page by page, we focus on the details, but as the story progresses we build a more global understanding of what the story is about.  Dr. Corvallis writes, be thankful to your hippocampi that you can make sense of a novel at all.

Dr. Corvallis suggests that although  the generativity spatial mapping is nonlinguistic, it may well underlie the generativity of language itself.  “In the rat these elements may be restricted to simple aspects like sounds or smells, and we may perhaps allow ourselves the luxury of believing our own experiences to be incomparably richer.  Yet the generative component itself probably has a long evolutionary history.  As Darwin famously put it:  ‘The difference in mind between man the the higher animals, great as it is, certainly is one of degree, and not of kind.’”

© Douglas Griffith and healthymemory.wordpress.com, 2017. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

Time Travel: The Ultimate Purpose of Memory?

October 28, 2012

Most of the time we think of memory as being a place of historical storage where old information and experiences are kept. But another way of thinking about it is as a vehicle for time travel (see the Healthymemory Blog Post, “Human Memory: A Machine for Time Travel”). You are able to travel to times long before you were born using what you have learned and your imagination. You can also project yourself into the future with science fiction or your own imagination. Actually we do quite a bit of projection in our daily lives, imagining what it will be like and making appropriate plans. Brain images of people when they are remembering the past and imagining the future show a great degree of overlap in the areas of the brain that are responding.

The distinguished memory researcher Endel Tulving found an unfortunate individual with amnesia who could remember facts but not episodic memories relating to past events in his life. When this person was asked about plans, be it for later in the day, the next day, or in summer, his mind went blank. Brain scans support this idea. When we think of a possible future, we tear through our memories in autobiographical memory and stitch together fragments into a montage that represents a new scenario. Our memories become frayed and reorganized in the process.1

So it appears that the ability to project ourselves forward in time, using what we have learned and experienced to guide the projection, might be the ultimate purpose of memory. Gestalt psychologists believe that in both the processing of information and its memory that laws were operating to create order and make information more meaningful. Emergence was an important concept in which new ideas emerged from the information at hand. These processes help us deal with the future.

Although our brains are working from the time we are born (and there is data indicating that they are working before we are born) to understand and make sense of the world in order to cope with it. In the early stages of life we are preoccupied with mastering language and moving about our environments. Consequently we rarely remember specific events before the ages of 2 or 3, when our autobiographical memories begin to develop And they develop slowly as it is difficult to remember much before our sixth birthday. We are also developing a sense of identity. When we are able to recognize ourselves in a mirror, we have achieved a critical stage of development. A child’s ability to imagine the future seems to develop in tandem with autobiographical memory. Obviously our culture and our families have a profound influence on these memories and our preparation for coping with the world. Our autobiographical memories continue to mature when we leave our parents. A ten year old can rarely relay a coherent life story, but a twenty year old can ramble on for hours. There is a “reminiscence bump,” where we are able to recall much more information that occurs in late adolescence.2 Consequently we are prepared or semi-prepared to assume responsibilities just in the nick of time.

1Robson, D. (2012). Memory: The Ultimate Guide. New Scientist, 6 October, p.33.

2Weir, K. (2012). A Likely Story. New Scientist, 6 October, 36-37.

© Douglas Griffith and healthymemory.wordpress.com, 2012. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

SuperAgers with a Super Memory

October 3, 2012

In a recent experiment1 SuperAgers were defined as individuals over 80 with episodic memory performance at least as good as normative values for 50- to 65-year olds. The performance of these SuperAgers was compared to two cognitively normal cohorts: age-matched elderly and 50- to 65-year olds. The brains of all three groups were compared using cortical morphometry.

With respect to memory performance, the SuperAgers performed better than both control groups (but the difference between the SuperAgers and the middle-age controls was not statistically significant, p>0.05). The sample consisted of 12 SuperAgers, 10 elderly controls, and 14 middle-age controls. The elderly control group performed significantly worse than the other two groups.

With respect to whole-brain cortical thickness elderly controls exhibited significant atrophy in the older cohort compared against the middle-aged controls in multiple regions across the frontal, parietal, and occipital lobes, including medial temporal regions important for memory. However, the whole brain cortical thickness analysis comparing the SuperAgers with the middle-aged controls did not reveal significant atrophy in the SuperAgers.

With respect to the thickness of the Anterior Cingulate Cortex, the thickness of the SuperAgers was higher than both the Elderly Controls and the Middle-Aged Controls. Somewhat surprisingly, only the difference between the SuperAgers and the Middle-Aged controls was statistically significant (p<0.05). However, the likelihood of achieving statistical significance increases as sample size increases. Research has indicated that the cingulate constitutes a critical site of transmodel integration related to episodic memory, spatial attention, cognitive control, and motivational modulation. It is unclear whether the SuperAgers were born with a particularly thick cortex or whether they resisted cortical change over time.

The relationship between brain and memory is an interesting one. The notion that more brain equates to more memory is fairly common, but this finding needs to be placed in context. Alzheimer’s cannot be diagnosed conclusively until an autopsy has been done. The key signatures for the diagnosis are amyloid plaques and neurofibrillary tangles. But these same signatures have been found in autopsies of people WHO HAD SHOWN NO SYMPTOMS OF ALZHEIMER’S WHEN THEY WERE ALIVE! So it would appear that these amyloid plaques and neurofibrillary tangles are a necessary, but not a sufficient condition for Alzheimer’s.

I remember reading an article when I was in graduate school about someone who had hydroencephalocele, which is more commonly called “water in the brain.” As a result of this condition, this individual had only about 10% of the normal volume of cortex. Yet this person led a normal life and earned a Bachelor of Science Degree in mathematics!

The plasticity of the brain is truly remarkable. Healthymemory believes that this plasticity is fostered by cognitive exercise and cognitive challenges. So, stay cognitively active and seek cognitive growth!

1Harrison, T.M., Weintraub, S., Mesulam, M.-M, & Rogalski, E. (2012). Superior Memory and Higher Cortical Volumes in Unusually Successful Aging, Journal of the International Neuropsychological Society, 18, 1-5.

© Douglas Griffith and healthymemory.wordpress.com, 2012. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

More on How Memory Works

November 4, 2009

  Understanding memory failures are key to understanding how memory works. Why can we not always recall the information stored in our brains? Well, one reason might be the enormous size of the brain in terms of nerve cells and synaptic connections. Memory theorists have made a distinction between information that is available in LTM and information that is accessible in LTM. There is much more information available in LTM than can be accessed at any one time. To retrieve information, the right retrieval cue must be used. This is known as the Principle of Encoding Specificity. The cue that was used to store the information is needed at the time the information is retrieved. If this cue cannot be found, or if the person is thinking in a different context, the information will fail to be retrieved. During these failed retrieval attempts we can often think of other items. We can also feel that we can almost recall the item. This is called the tip of the tongue (TOT) phenomenon. This also reveals yet another type of memory, metamemory. Metamemory is knowledge you have about your own memory. If asked a question about which we know nothing, we will not even bother to try to retrieve it. If we think we might know, we shall try to retrieve it. What is especially annoying is when we know we know something, but just can’t remember it. Then, at some later time, when we are not even trying to remember, the answer will come to us. Why this happens and techniques you can use to prevent this from happening will be discussed later in this blog.

LTM can be subdivided into other types of memory. Episodic memory refers to events we have personally experienced, that is, episodes. Amnesia, when people forget who they are and where they came from is commonly referred to as a loss of memory Actually, it is usually a loss of a specific type of memory, autobiographical memory, which is a component of episodic memory. This is the memory of someone’s own specific history. When someone loses all memory, they lose the ability to function. The final stages of Alzheimer’s disease provide a graphic example of what it means to lose all memory. What something was, when and how it occurred are all examples of episodic memory. Remembering that the Declaration of Independence was signed on July 4, 1776 in Philadelphia is an example of episodic memory. However, the wider significance of that event would be stored in semantic memory. Semantic memory is the storehouse of general knowledge. To solve a problem or to answer an essay question on an exam requires semantic memory.

 

 

© Douglas Griffith and healthymemory.wordpress.com, 2009. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.