Download physiology of memory and learning

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‫االسراء اية ‪58‬‬
Physiology of Memory
and Learning
Memory an Learning
 Learning
and memory are higher-level
functions of the nervous system.
 Learning is the neural mechanism by which a
person changes his or her behavior as a result
of experiences.
 Memory is the mechanism for storing what is
learned.
Learning
♦ Def
 It is the ability of previous experiences to modify

the inborn reactions or create new ones

or
It is the acquisition of knowledge or skills as a
result of experiences and consequently it can alter
behavior on basis of this experiences
 Learning is the process by which we acquire
knowledge about the world (Eric Kandel, 2000)
 Learning refers to a more or less permanent change
in behavior which occurs as a result of practice
Learning
 Types
1. Associative
2. Non-associative
(Relation of one
stimulus to another)
(ignore or react )
a. Classic conditioning
a. Habituation
b. Operant
conditioning
b. Sensitization

Associative Learning
In this type of learning, the subject learns about the
relationship that can associate one stimulus to
another
 It is a conditioned process which results in the
formation of learned responses called conditioned
reflexes
 Conditioned reflex is an automatic response to a
stimulus (conditioned stimulus) which did not
previously evoke response acquired by repeatedly
associating this stimulus with another stimulus
(unconditioned stimulus)
a) Classic Conditioning
This type of conditioned reflexes was 1st described
by Pavlov (Russian Physiologist)
 He noticed that his experimental dogs salivate just
on seeing the animal house keeper who used to feed
 Some sort of association had developed in the brains
of these animals between visual stimuli related to
seeing the housekeeper (conditioned stimulus) and
food ingestion (unconditioned stimulus for
salivation when food is placed in mouth)

a) Classic Conditioning
a) Classic Conditioning

This type of conditioning can be integrated a
different levels of CNS
 Requirements:
 1) CS applied before US
 2) Pairing must occur several times
 3) No separation between the CS and US
a) Classic Conditioning
b) Operant Conditioning

In this type of conditioning the subject is taught to
perform some voluntary action in response to a
particular stimulus (visual or sound stimulus) that
alert him to perform the learned action in order to
obtain reward to avoid punishment
 Alerting signal acts as conditioned stimulus whereas
pleasant or unpleasant event that follow
performance of learned response represents
unconditioned stimulus
b) Operant Conditioning
b) Operant Conditioning
Example:
 Car driver and traffic light
 The car driver stops the car on seeing the red traffic
light and drives on seeing the green light
Integration:
 Hippocampus and amygdala are important in linking
the stimulus to the operation
 Integration occurs in CC especially orbitofrontal
cortex

Non-associative Learning
In this type of learning, the subject learns whether
to ignore or react to a certain stimulus
 It is a simple way of learning that does not need
association between 2 stimuli
 It is 2 types;
 A) Habituation
 B) Sensitization

Habituation
It is a gradual decrease in the response to stimulus
when it is frequently repeated
 It is simple and widespread
 Examples:
 A loud and unexpected sound produces looking
towards the source of sound, change in heart rate,
and change in blood pressure
 If the sound turns to be insignificant, its repetition
results in little or no response
Habituation

It is a stimulus specific e.g. traffic noise and mother
and baby
 Mechanism:
 Repetition of the stimulus close Ca channels in
presynaptic neurons →↓ Ca influx →↓ release of
neurotransmitters →↓ behavioral responses to the
stimulus
Habituation

Experiments performed in Aplysia californica

Sensitization
It is a potentiation in the response to stimulus (painful
or pleasant) when it is frequently repeated
 It is simple and widespread
 Examples:
 One normally ignore stray dogs by habituation, but if
he is bitten, he will become more attentive and
develop aversion reaction to them for long time
 Stimulus specific:
 One who is bitten by dogs will not be afraid of
donkeys or cows

Sensitization
Mechanism:
 Strong or noxious stimulus → facilitating
interneurons (serotonin) →↑ cAMP in presynaptic
neurons → block of K channels → depolarization of
presynaptic neurons → keep Ca channels open →↑
Ca influx →↑ release of neurotransmitters →↑
behavioral response to mild stimuli
Sensitization
Sensitization
Memory

Def

memory is the process by which that knowledge of the
world is encoded, stored, and later retrieved (Kandel (2000),
 Memory is a phase of learning

learning has three stages: 1. acquiring, wherein one
masters a new activity . . . or memorizes verbal
material . . . 2. retaining the new acquisition for a
period of time; and 3. remembering, which enables
one to reproduce the learned act or memorized
material
Memory

Def

It is the ability of the brain to store information and recall it
at later time or

Capacity of the brain:
It is limited (total capacity of brain is 3x 108 bits)
 So, informations entering brain are either;

A.
B.
Selected and stored (1%) → most important
Other (99%) → are neglected and forgotten
Memory

Information Unit:

It is bit
A bit is the simplest form of sensory experience i.e. figure,
sound, touch , or smell
All sensory systems send information to brain at 50 bit/sec
E.g. during reading 40 bits/sec, during mental calculation 12
bits/ sec, and during counting 3 bits /sec
Average rate of flow of information is 20 bits/sec
For learning a language about 40- 50 millions bits should be
stored in memory
To store 1 bit, 10 neurons are required







Memory
Classification of memory:
1. Sensory Memory
• Duration: very short (about 0.5 seconds)
• Capacity: very small (15-20 bits)
• Entry into storage: automatic during perception
• Access to storage: very rapid
1. Vision: iconic memory
2. Hearing: echoic memory
• Mechanism:
• 1. Stimulation of reverberating circuits → repeated
activation of neurons
• 2. Synaptic sensitization if sensory experience coupled with
painful stimuli
1. Sensory Memory
• Mechanism:
• 3. Posttetanic potentiation: multiple stimuli at
presynaptic terminal →↑ Ca content in presynaptic
terminal →↑ release of neurotransmitters
• Mechanism of forgetting:
• 1. Fading (spontaneous and gradual decline in the amount
of information)
• 2. Extinction (spont. disappearance of information from
memory)
2. Short-term Memory

Duration: (min to hours)
 Capacity
– Small bits of informations
– Miller’s magical number: 7±2 chunks of information

Entry into storage: verbalization (describing the
items in words)
 Recall or access to storage: rapid
 Mechanism:
 Made by formation of temporary memory traces
2. Short-term Memory

Memory trace:

Is a newly developed pathway or signal transmission
resulting from facilitation of new synapses → creation of
new circuits in the brain
This occurs by
1. Long term potentiation of synapses
2. Changes in physical properties of postsynaptic
membrane → ↑ sensitivity to chemical transmitters
Mechanism of forgetting:
New information replaces old





3. Long-term Memory

Duration: (hours to years )
 Capacity
– Very large
– Information stored according to its significance

Entry into storage: practice or and punishment or
reward
 Recall or access to storage: slow
 Mechanism:
 Made by formation of memory engrams (longlasting memory traces) formed by structural
changes in presynaptic terminals
Long-term potentiation





1. The binding of glutamate to its NMDA receptors and
simultaneous depolarization of the postsynaptic membrane
causes the NMDA receptor channels to open.
2. This opening of the NMDA receptor channels allows
Ca2+ to enter.
3. The entry of Ca2+ into the postsynaptic neuron causes
long-term potentiation in that neuron.
4. The entry of Ca2+ into the postsynaptic neuron also
activates nitric oxide synthase, causing nitric oxide
production.
5. The nitric oxide then acts as a retrograde messenger,
diffusing into the presynaptic neuron and somehow
causing it to release more neurotransmitter.
3. Long-term Memory

Mechanism:
 memory engrams made up by;
 1. increase in number of vesicles
 2. increase in number of presynaptic terminals
 3. increase in release sites of chemical transmitters
 4. generation of new receptor sites
 5. long term potentiation
 Engrams remain for long time up to several years
 Formation of new engrams requires protein
synthesis
3. Long-term Memory

Mechanism of forgetting:
1. Proactive inhibition by previously stored materials
(more common)
2. Retroactive inhibition by subsequently stored
material
4. Permanent Memory

Duration: (permanent)
 Capacity
– Very large

Entry into storage: very frequent practice
 Recall or access to storage: very rapid (recall not
affected by brain injury (like name, write, and read)
 Mechanism:


Advanced stage of long-term(permanent engrams)
Mechanism of forgetting :
 No forgetting
Phases of memory

Encoding-information for each memory is assembled from
the different sensory systems and translated into whatever
form necessary to be remembered. This is presumably the
domain of the association cortices and perhaps other areas.
 Consolidation-converting the encoded information into a
form that can be permanently stored. The hippocampal and
surrounding areas apparently accomplish this.
 Storage-the actual deposition of the memories into the
final resting places–this is though to be in association
cortex.
 Retrieval-memories are of little use if they cannot be read
out for later use. Less is known about this process.
Encoding of memory








It means classification and placing memory items in their
proper memory stores in brain
Brain areas concerned with encoding of long term memory;
1. Hippocampus (major central role) all bits of information
go to it first
2. Amygdala (emotional memory)
3. Basal forebrain (Nucleus basalis or Meynerts nucleus)
4. Noecortex
5. Mammillary body of hypothalamus
6. Orbitofrontal cortex
Encoding of memory
Select important informations
(reward or punishment)
All bits
Hippocampus
store
Amygdala
store
(Temporal lobe)
Mamillary
body
Cholinergic projections
Cholinergic projections
Cholinergic projections
Basal forebrain
Meynerts Nucleus
Neocortex
store
Orbitofrontal
cortex
Consolidation of memory



1.
2.
3.
It means the process of conversion
of STM to LTM
It takes from 5 min to 2 hrs
It is interrupted by
Deep anaesthesia
Brain concussion
Electroconvulsive therapy
Brain Regions involved in Consolidation of
memory
• Hippocampus
• Anterior & lateral
temporal lobe,
• Medial temporal lobe
• Amygdala
Hippocampus and Consolidation of memory
• The hippocampal region is critical for the consolidation of
information in long-term memory
Evidence
•
Three major excitatory neural components of the hippocampus
Perforant pathway
• forms excitatory connections between the parahippocampal cortex
and the granule cells of the dentate gyrus
Mossy fibers
• connect the granule cells of the dentate gyrus to the CA3 pyramidal
cells
Schaffer collaterals
• connect the CA3 pyramidal cells to the CA1 pyramidal cells
Disorders of Memory
1) Amnesia → loss or impairment of memory
It may be;
a) Retrograde amnesia
•It means inability to recall memories from the past
(retrograde: going backwards), that is from the long- term
memory stores.
•Transient brain malfunction erase 1ry memory
•It usually follows a traumatic event that interferes with the
normal activity of the brain, such as a strong brain
concussion and vascular strokes
Disorders of Memory

•
b)Anterograde amnesia
It is the inability to store new information in the long-term
memory for later recall.
• It usually results from lesions of the medial portions of the
temporal lobe, a region that include the hippocampus,
amygdala, and the adjacent areas of the temporal

•
•
•
c) psychogenic or hysterical amnesia
Rare
Sudden loss of memory of all information
Exposure to severe psychological stress
Disorders of Memory
2) Senile dementia and Alzheimer disease
 It occurs in old age (senile dementia) and middle age
(Alzheimer), but it can occur at any age
• It is characterized by impairment of memory, lack of
concentration, inattentiveness
• Incidence: 10-15 % after age of 65 years
• Mechanism:
• Loss of cholinergic terminals that diffuse from nucleus
basalis to neocortex, amygdala and hippocampus
Dr. Abdel Aziz Hussein, Mansoura Faculty of Medicine