MEMORY
Overview of Topics
Lesson Objectives
Definition of Memory
Nature of Memory
Types of Memory
Memory Model
Brain Lesions & Amnesia
Retrograde Amnesia
Anatomy of Memory
Brain Areas & Memory
Types of Memory & Brain Areas
Functional Memory System
Classic Cases of Memory Dysfunction
Summary
TERMS you should know
Lesson Objectives
- Explain the difference between learning and memory.
- Discuss the differences between declarative and procedural memory.
- How do the above two classifications of memories differ with regard to brain areas involved in memory storage?
- Explain what is meant by shrinking retrograde amnesia.
- Explain memory consolidation using Loftus' model.
- Explain the concept of working memory.
Definition of Memory
- Learning
- The acquisition of new information.
- Memory
- The retention of learned information - the acquisition, storage, and retrieval of information.
- Related to all cognitive and emotional functions.
- Not a discrete entity - rather the "inherent process of the nervous system to acquire, store, and retrieve information"
- As such it represents the basic workings of the nervous system.
The Nature of Memory
- Process that results in a relatively permanent change in behavior.
- No identifiable specificity of storage but throughout the brain.
The Nature of Synaptic Change
- Gardner-Medwin (1973) - electrical stimulation of neuron can produce either a brief or long-lasting change in synaptic transmission.
- Brief high frequency stimulation - increased response magnitude.
- long-term potentiation - effect may last for days to months.
- With repeated stimulation there is an increase in dendrites and thus synapses.
- Also increase in vesicles, post-synaptic membrane, & size of dendritic spines.
- Other Changes occur in neurons in contact with each other that are active at the same time.
- Modifications may be:
- Presynaptic due to alterations in presynaptic proteins and modification of K+ channels.
- Postsynaptic such as long-term depression resulting from desentisized AMPA receptors.
- The effect is that they don't stay open as long resulting in a reduction in the EPSP.
Types of Memory
The term memory is a logical construct that subsumes many different processes and
requires the function of many different brain areas. Research in recent years has
provided information necessary to many of the various components of memory and identify
associated brain regions. This section will outline some of the most important types of
memory and this same outline of terms will be later related to brain research identifying
specific areas of the brain that are most important in the proper function of these
different types.
Declarative [WHAT]
Memory for facts and events accessible to conscious recollection. Memory for things that one can recall and declare. Easily formed and forgotten.
Sensory -[Encoding]- quickly decreasing sensory representation of event
Episodic -- Memory for past personally experienced events.
Semantic -- Memory for facts.
Non-Declarative [How]
Short-term Memory -- Temporary storage with limited capacity. Involves multiple sites and continued rehearsal. Storage without distraction.
Long-term Memory - Memory that has been consolidated or stored so that it is available after distraction.
Working Memory - short term recall & temporary storage of information to complete a task. Thought of as "working with memory" - the plan.
Source Memory - most readily lost due to the limitation in associations.
Relational Memory - multi-modality. May have good short-term memory with one modality but not another.
TOP |
MEMORY MODEL: Modified from Loftus (19 )
This is a linear model that considers memory as a process beginning with sensory
registration and finally leading to the consolidation of some information into long-term
and/or remote memories.
|
Stimulus- |
Sensory Registration |
Attention- |
Short-Term Memory |
Consolidation- <-Retrieval |
Long-Term Memory |
Remote Memory |
1. Sensory Register (icon)
2. Short-term Memory
a. Brief storage of information.
b. May be held for longer time by rehersal.
c. Without rehearsal information quickly lost.
d. Limited as to the number of stimuli that may be retained here.
3. Consolidation
a. Stimuli that have an effect on the limbic system result in it registering its significance and initiating the command to store the information.
b. Consolidation is necessary for and effects the long-term storage of information.
4. Long-Term Memory
a. Represents the storehouse of information that has been consolidated and made relatively permanent.
b. Although the limbic system is the essential structure initiating consolidation, the actual memory stores are throughout the nervous system.
c. Their location is a function of the brain structures involved in processing the information.
d. Receptors to projection cortex have very little storage capability as they are used to process all information for that modality and thus are subject to interference.
e. The sensory association cortex is more important as it is at this level that patterns of neurons can be unique and sleective processess information with less interference.
f. Short- & Long-term memory are not seperate entities but highly interdependent; both contribute to the other.
4. Remote Memory
a. Represents the storehouse of information that was acquired early and serves as the foundation for later memories.
b. The continuing process of memory acquisition involves linking new memories to old.
c. The process can be thought of as like building a brick wall. New ones are laid on top of old.
d. This is the reason that memories are lost from the present back in time with brain injuries or dementias.
Brain Lesions & Amnesia
Much of the early information regarding structures of the brain and types of memory loss was obtained from the study of individuals who suffered traumatic brain injury or other types of neurological lesions.
- Retrograde
- Loss of memory from one point back in time.
- Anterograde
- Loss of memory from one point foreward. Called post-traumatic anmesia (PTA) following traumatic brain injury.
- Transient Global Amnesia
- brief cerebral ischemia produces sudden loss of memory (minutes or days; retrograde).
Retrograde Amnesia (Russell, W. R., & Nathan, P.W.)
1. RA prevents events from being retained, or if retained, cannot be recalled.
2. Duration of RA varies with severity. Shrinking occurs by time not by order of importance.
3. Many non-head-injured individuals are unable to describe what happened a week ago unless there is some special experience to remind them.
4. Recent memories are more vulnerable than remote, but it is remarkable that recent memories for important events should be so completely obliterated from memory as they often are.
5. RA increases with PTA Duration
6. In traumatic cases the ability to recall events since the injury may have recovered well.
7. Barbiturate hypnosis may separate hysterical from organic amnesia.
RA Duration as a Function of PTA Duration
|
RA Duration |
<1 hr |
1-24 hr |
1-7 days |
7 days |
|
Minimal |
18% |
2% |
2% |
- |
|
1 Min |
68% |
70% |
30% |
24% |
|
1-30 min |
12% |
26% |
42% |
36% |
|
.5-12 hrs |
2% |
2% |
18% |
12% |
|
.5-2 days |
- |
- |
6% |
14% |
|
2-10 days |
- |
- |
2% |
12% |
|
10 days |
- |
- |
- |
2% |
|
Average |
1.98 |
2.28 |
3.02 |
3.60 |
Anatomy of Memory
Neural Systems
Different Brain Areas Process Different Aspects of Memory
Encoding
- Pictures - right prefrontal & bilateral parahippocampus
- Words - left prefrontal & left parahippocampus
- Hemispheric encoding retrieval asymmetry - Left hemisphere - greater in encoding & Right in retrieval.
- Autobiographic (episodic) different area than semantic.
Memory consolidation [hippocampal system]
- Permanent storage in cortex where processed & held in ST memory
- Further medial temporal & midline diencephalic processing leads to
- Consolidation leading to Long Term Memory.
Hippocampus - impaired spatial location recognition.
- declarative (relationships among stimuli)
- global amnesia.
- Declarative memory impaired not procedural
- Encoding - more rostral hippocampal
- Retrieval - more posterior (caudal)
- required for delay conditioning
- larger in animals with improved spatial ability.
- larger in males of many species.
Cortical Memory Stores
- KC - left frontoparietal & Right parietooccipital cortex damage
- Associative Learning
- Loss of personal information (episodic or autobiographical)
- Difficulty acquiring semantic memory.
- Neocortical damage alone - no such amnesia - minor role in memory formation, however, it is clearly involved in the storage process.
- Extrastriate Cortex
- object recognition memory (McDonald & White(93)
- Anterior cortex - episodic memory
- Posterior cortex - semantic memory
Procedural - basal ganglia & Cerebellum
- Skill learning
- Non-associative learning - habituate or become sensitized.
- Caudate
- response recognition memory
- Dorsal striatum (Basal Ganglia)
- procedural (S-R association)
- Priming - neither hippocampus or basal ganglia involved
- Perceptual - form - bilateral occipital
- Conceptual - meaning - left frontal cortex.
- Conditioning
- Kesner (90,91,93,98)
Cognitive map vs latent learning
Stability of Memory
Learning & Memory Change across the Lifespan
Types of Memory & Specific Brain Areas
- Gabrieli (98) - "First knowledge in any domain is distributed over a sepcific, but extensive, neural network that oftens extends over several lobes. Second, some localization appears to be a consequence of how various classes of knowledge interact with different perceptual and motor systems."
- Learning - Often activity shifts across areas during learning so that it appears to involve a complex set of interacting neural networks.
- Specific genetic abilities to learning and memory
Declarative [What]
Diencephalon (Hippocampus, MMB, dorsomedial & anterior thalamic nuclei impair memory consolidation and recall.
Perirhinal cortex - results in most severe memory deficit.
Amygdala - only mild deficits. Sensory -- [Encoding] - Left Hemisphere > Right.
Pictures - Right prefrontal, bilateral parahippocampal area
Words - Left prefrontal, Left parahippocampal area
Episodic -- neocortex, particularly Right Frontal & Temporal Lobes
Semantic -- -- neocortex, particularly Temporal Lobes
Non-Declarative
Procedural memory - Basal Ganglia, Motor Cortex, Cerebellum
Priming - skills [Non-Declarative]
Conditioning -
Short-term Memory -- CNS
Long-term Memory - CNS
Working Memory -- Frontal Cortex {doesn't produce amnesia}
Source Memory - Neocortex
Relational Memory - CNS.
TOP |
The Functional System
Levels of Processing Reading Speech comprehension MMB - information processing and selective retrieval. Hippocampus - attention & consolidation.
Clinical Memory Assessment
Material Modality Tests - measure short term memory Long-term memory - delay (distraction)
Non Neurological Factors
Forgetting vs. Interference Learning
By design - we all have memory loss due to interference learning. Levels of processing vs. Uniqueness (Luria's Model)
Use It or Lose It
Practice with Feedback.
Summary
1. Many regions of the brain involved in learning & memory.
2. Different types of memory mediated by different neural areas.
3. Same brain area may be involved in different types of memory.
4. Learning may involve many different brain regions
5. Some types that appear similar may involve different brain areas.
Classic Cases of Memory Dysfunction
HM - Scoville (1953) bilateral hippocampal resection on H.M. and made him
amnestic. Impaired memory storage new memories but not memory stores.
- HM bilateral 8 cm resection of medial temporal lobes
- Had partial retrograde amnesia (10 yrs)and extreme anterograde amnesia.
- Normal short-term memory and remote memory.
- Thus, Declarative memory disturbed but procedural memory intact
NA - dorsomedial thalamus, MMB, MTT - AA.
RB -
Altzheimers disease - hippocampal (consolidation) and prefrontal (working memory) produce first signs of memory loss.
Good recall of past - can't consolidate new memories.
Korsakoff's - dorsomedial thalamus, MMB, - AA.
Poor recall of past - confabulate
No damage to hippocampus & temporal cortex.
The case of S - Luria - The Mind of the Mnemonist. Total recall synesthesia Paid a price - not able to reason, categorize, or see order. Little ability to deal with metaphors (interpreted them literally).
Summary
Behavioral flexibility and adaptability are dependent upon the organism's ability to both store and retrieve information and to modify the memory stores. Memories are, thus, not fixed or unchanging entities. Rather they represent enhanced patterns of neuronal interconnections which are subject to continual change.
Procedural memory represents motor or skill learning which is memory without verbal mediation and thus without record. Such memories are slow to acquire but more resistant to change or loss.
Declarative memory is memory for facts. It is fast changing, quick to acquire but quick to be lost. Much of the loss is by design. Considerable information activates the receptors but is not retained. We attend to meaningful or relevant stimuli and ignore unchanging or uninformative information.
Important information enters short-term memory stores and may be enhanced by rehearsal. If such information is associated with limbic system activity it may be consolidated or transferred to long-term memory stores.
While the limbic system is important in determining what information is converted to long-term memories, the actual memory stores represent multi-modal network of neurons throughout the nervous system.
Most loss of information is due to interference learning rather than forgetting. Neurons close to the receptors or effectors, have little uniqueness. They are used repeatedly to process or respond to information. However, neurons sufficient in number and removed from the receptors and/or effectors may be very selective and subject to less interference learning. Neurons in the association cortex best represent those which will play an important role in the memory stores.
Remote memory simply refers to memories that were acquired early. They represent the foundation memories upon which more recent memories are build. Consider the process of identifying a new object or word. One has to find a link from this new stimulus to existing memory stores. Thus, forming new memories involves associating new information with previously stored information. Since early acquired information is the foundation for new memories and may be linked to many more new memories, such memory is less subject to change and/or loss.
Terms You Should Know
|
Declarative Memory |
Memory consolidation |
AMPA receptors |
|
Procedural Memory |
Transient global amnesia |
Anterograde amnesia |
|
Short-term Memory |
Retrograde amnesia |
MMB |
|
Long-term Memory |
Perirhinal cortex |
Medial temporal lobes |
|
Working Memory |
Relational Memory |
|
Conclusions
1. Duration of memory loss is correlated with severity of injury to the brain.
2. Recovery of distant memories first
3. After severe injury there may be a permanent RA of several days duration which may include events of great importance to the patient.
4. Recovery occurs according to time not importance of events.
5. Long RA is almost always associated with long PTA.
Links to Associated Areas
