Learning & Memory

 

INTRODUCTION

 

A. Definitions

 

1. Learning:  acquisition of new information by the nervous system

 

2. Memory:  storage and retrieval of learned information

 

3. Forgetting:  loss of information from storage

 

B. Cellular Basis of Memory

 

1. Change in synaptic transmission due to use:  the reliability (probability) of excitation transmission of certain synapses is increased with use (increase sensitivity, potentiation, synaptic plasticity) due to

 

a. glutamate released from the presynaptic ending binds to NMDA-Glu receptors which open channels increasing the postsynaptic permeability of Na, K, and Ca

 

b. Ca moves into the postsynaptic neuron, activating cAMP which in turn initiates an internal cascade resulting in an increase number of excitatory receptors in the postsynaptic membrane

 

c. Also, postsynaptic intracellular Ca activates a proteins in the cell nucleus which cause the production of neurotropin, which in turn stimulates synaptic development

 

 

2. The effectiveness of the above mechanism depends upon the strength of the presynaptic input -- the more intense the input (higher stimulus frequency, greater presynaptic recruitment, repetition) – the greater the effect

 

3. If activation ceases, the effect may gradually die away and the synapse may revert to its previous state

 

Note:  (1) and (2) above underlie learning and storage; (3) underlies forgetting

 

 

MEMORY CATAGORIES

A. Declarative Memory (also called Explicit memory):  stored information available to consciousness and which can be expressed in words or by other means, including

 

1. Words and their meanings

2. Autobiographical narratives (e.g. events; may be stored as pieces of information rather than complete events)

3. Learned facts

4. Tunes that can be hummed or played or other sounds that can be reproduced

5. Mental pictures that can be reproduced (e.g. draw a map)

 

Note:  sometimes declarative memory is limited to only those information that can be expressed in language (i.e. 1-3 above)

 

Note:  requires consciousness for acquisition and recall

 

B. Procedural Memory (also called Implicit or Reflexive or Nondelarative memory):  stored information which is unavailable to consciousness and can be exhibited without conscious reflection, including

 

1. Motor skills

2. Priming cues:  memory stored as a result of previous exposure even if the person is unaware of the exposure (e.g. advertisements)

3. Unconscious associations, including emotional associations

4. Problem solving; insight

 

C. Emotional Memory

 

1. Emotional evaluations stored along with the stimuli that induced them

 

Note:  Emotional memory is sometimes included with Declarative memory because it can be consciously recalled

 

 

MEMEORY STAGES (stages in the acquisition of information)

 

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A. Immediate Memory:  ability to hold immediately acquired information for a few seconds

 

B. Short-Term Memory:   ability to hold acquired information for up to several minutes

 

C. Intermediate-Term Memory:  ability to hold information for minutes to hours

 

D. Long-Term Memory:  ability to hold information for days to years

 

     Note:  Long-Term Memory includes Remote Memory, memories that are deeply embedded and may last a lifetime

 

E. Working Memory:  a subset of short-term and intermediate-term memory which refers to the ability to hold information sufficiently long to carry out some action; also, items in long-term memory can be retrieved into working memory

 

F. Consolidation:  process by which shorter term memory is converted to longer term memory

 

 

IMPORTANCE OF CONTEXT

 

A. Phenomenon:  storage of relatively meaningless information is very limited – about 10 objects.  However, if the information acquisition increases greatly if it is

 

1. significant

2. related to past memories

3. has a discernable pattern

4. is accompanied by strong emotion

 

Example:  remembering positions in chess by chess masters and by beginners:

 

A.  Position from a world championship game

 

B.  Random placement of chess pieces

 

C.  Ability to recall the position of the pieces in A after brief exposures

 

D.  Ability to recall B after brief exposures    

 
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FORGETTING

 

A. Properties

 

1. Characteristic of normal memory

 

     Subjects asked to identify characters in popular television shows:

 

 

 

        Note:    “Before ECT” represents the normal response;  ECT = Electroconvulsive Therapy

 

2. Forgetting is an essential part of effective memory; inability to forget interferes with recall

 

3. Forgetting is a normal part of aging

 

B.     Amnesia:  abnormal forgetting

 

1. Retrograde amnesia:  difficulty in retrieving previously established memories

 

2. Anterograde amnesia:  inability to establish new memories

 

Note:  unconsciousness (traumatic concussion, ECT, or other causes) leads to retrograde amnesia for events preceding the precipitating cause

 

 

NERVOUS SYSTEM BASIS OF MEMORY

A. Stages

 

1. Brain receives information from the sensory systems

 

2. After the sensory information is processed by the sensory association cortex, it is held in short-term working memory and consolidated into intermediate-term working memory

 

3. The information may then be consolidated into long-term memory

 

B. Brain regions involved in declarative memory

 

1. Prefrontal cortex participates in the storage of short-term, intermediate-term, and working memories

 

2. Hippocampus

 
 
a. Critical structure for the consolidation of shorter-term declarative memory into long-term declarative memory

 

b. Bilateral removal blocks the development of long-term declarative memories

 

c. The hippocampus is described as a memory staging area that connects the multitude of stimuli associated with various events

 

d. The hippocampus makes numerous connections with temporal, frontal, and parietal lobes

 

e. The hippocampus is not critical for procedural memories

 

3. Mamillary bodies of the hypothalamus act with the hippocampus for memory consolidation (pathophysiology example:  memory loss due to mamillary body degeneration in chronic alcoholism due to vitamin B1 deficiency)

 

4. Long-term memory is localized in multiple regions (i.e., parts of the frontal, temporal and parietal lobes); this is one reason why long-term memory is resistant to localized cerebral injury

 

 

C. Brain regions involved in procedural memory

 

1. Basal ganglia striatum (caudate nucleus and putamen)

2. Cerebellum for fine, complex movements

 

D. Brain regions involved in emotional memory:  Limbic system, particularly the amygdala

 

LEARNING STRATAGIES FOR DECLARATIVE MEMEORY

 

1. Do not do those things that disrupt hippocampal function (e.g., stress, loss of sleep, too much alcohol, high blood pressure)

 

2. Intense attention has a positive effect on declarative memory, but does not usually affect procedural memory (e.g., listening to the radio could interfere with learning new facts, but not affect learning a mechanical skill)

 

3. If possible, involve multiple sensory systems in the acquisition of information (e.g., lecture involves visual and audible stimuli and perhaps active participation compared to simply reading the notes)

 

4. Repetition is critical for the transfer of information into long-term memory

 

5. Allow time for the consolidation of the short-term or working memory into long-term memory

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6. During the consolidation phase, it is important to minimize interference from other information