Posts Tagged ‘semantic 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 MEMORY ILLUSION

January 26, 2017

“THE MEMORY ILLUSION” is the title of a book by psychologist Julia Shaw, Ph.D.   The subtitle is “Remembering, Forgetting and the Science of False Memory.  This is an outstanding book on a very important topic that is well-written by an excellent author, one that is strongly recommend reading by HM.  Due to the importance of this topic, many posts  will be written based on the book.

There are many misconceptions regarding human memory.   This book is devoted to correcting the most egregious of these misconceptions.  People tend to think of memory in a very limited sense.  It’s thought of as something you need during tests, and as something that fails you when you can’t recall a name.  But readers of the healthy memory blog should know that memory is central to all cognition and to our very being.

Consider someone in the last stages of Alzheimer’s.  That person no longer remembers who he is, what he did during his life, his immediate  family and, of course, his friends.  Absent memory there is no you-ness.

There are different types of memory.  Semantic memories are our knowledge about the world.  Procedural memory is about how different procedures are performed such as riding a bike.  Autobiographical memory is about ourselves, and episodic memory is about the specific events or episodes that occurred during our lifetimes.

There is also something important regarding both how our memories work and how to make them work better.  This is called metamemory.   We need to be aware of how our memories fail, so we do not fall victim to them, and so that we can compensate for their failures and shortcomings.

As Dr. Shaw writes, “Any event, no matter how important, emotional or traumatic it may seem, can be forgotten, misremembered, or even entirely fictitious.”

As she also writes, “Due to our psychological and physiological configuration all of us can come to confidently and vividly remember entire events that never actually took place.”

And as she continues,  “The Memory Illusion” will explain the fundamental principles of our memories, diving into the biological reasons we forget and remember.  It will explain how our social environments play a pivotal role in the way we experience and remember the world.  It will explain how self-concept shapes, and is shaped by our memories.  It will explain the role of the media and education in our misunderstanding of the things we think memory is capable of.  And it will look in detail at some of the most fascinating, sometimes almost unbelievable, errors, alterations and misapprehensions our memories can be subject to.”