1.
CENTRAL NERVOUS SYSTEM
LEARNING & MEMORY
Dr. Mehvish

2.
• Higher mental function
• Involvement of limbic system, higher cortex and cerebellum
• Memory laid down in stages
• Memory is generally stored as concepts not verbatim (word by word)

3.
The Holistic Theory Of Thoughts
A thought results from a “pattern” of stimulation of many parts of the
nervous system at the same time, involving the cerebral cortex,
thalamus, limbic system, and upper reticular formation of the brain
stem.
means that the whole is greater than the sum of its parts
Nature of thought
Pleasant or unpleasant
Associated with memory

4.
• Thoughts are mental cognitions—our ideas, opinions, and beliefs
about ourselves and the world around us. ...
• Shaped by life experiences, genetics, and education
• Generally under conscious control.
• In other words, if you are aware of your thoughts and attitudes, you
can choose to change them.
• Thoughts can be consolidated into memories

5.
Learning:
Acquisition of knowledge or skills. It alters the behavior of a person
on the basis of past experience
Memory:
Acquisition, storage and retrieval of information for later recall.
Memory Trace:
Neural change responsible for retention or storage of knowledge

6.
Consolidation
The process of transferring and fixing short-term memory traces into long
term memory stores
Storage (encoding)
Process by which information is converted into ‘usable’ form to be stored in
brain
Retrieval (decoding)
Process of remembering the stored information
Forgetting
Inability to retrieve the stored information

7.
When an established memory is actively recalled, it becomes labile (unstable
or subject to change) and must be re-consolidated into a re-stabilized,
inactive state.
New information may be incorporated into the old memory trace during
reconsolidation

8.
BASIS OF MEMORY- SYNAPSE/ SYNAPTICE TRANSMISSION
Memories are stored in the brain by changing the basic sensitivity of
synaptic transmission between neurons as a result of previous neural
activity.
The new or facilitated pathways are called memory traces
Positive and Negative Memory
“Sensitization” or “Habituation” of Synaptic Transmission

9.
CLASSIFICATION OF MEMORY

10.
Habituation is negative memory
i.e. brain has the capability to ignore information that is of no consequence
(neither rewarding or punishing). This capability results from inhibition of the
synaptic pathways for this type of information
Sensitization is positive memory
i.e. for incoming information that causes important consequences such as
pain or pleasure, the brain has a different automatic capability of enhancing
and storing the memory traces, which is positive memory. It results from
facilitation of the synaptic pathways

11.
Based on duration
• Short term memory
For seconds or minutes
• Intermediate long term memory
For days to weeks but fades away
• Long term memory
For years or even life time

12.
Declarative memory (what)
Involves awareness or consciousness
• Episodic memory
memory of events & objects etc
• Semantic memory
memory of words, language, education etc
Nondeclarative memory/ Skill (How)
• Does not involve awareness
• Learning to use keyboard, cycling, acrobatics etc

13.
/SKILL
/Recognition

14.
MOLECULAR MECHANISMS INVOLVED

15.
SHORT TERM
• Circuit of
reverberating
neurons
• Presynaptic
facilitation or
inhibition
INTERMEDIATE-LONG
• Habituation
• Facilitation
LONG TERM
• Structural changes in
synapse
• Long term
potentiation &
depression (LTP & LTD)
• Rehearsal/
consolidation

16.
SHORT TERM MEMORY
• For a few seconds to a few minutes at a time but lasting only as long as
the person continues to think about the numbers or facts
• Continual neural activity resulting from nerve signals that travel around
and around a temporary memory trace in a circuit of reverberating
neurons
• Presynaptic facilitation or inhibition
Working memory
“the erasable blackboard of the mind”
temporarily holds and interrelates various pieces of information relevant
to a current mental task

17.
• A type of short term memory
• Stored in prefrontal association area
• New & stored information is brought into working memory for
analysis/integration
• Important for current mental task
• Reasoning, planning, judgment, multiple tasking at one time etc
• Correlates with intelligence
• More the working memory more intelligent and efficient is the
person
• Affected by stress

18.
Reverberating circuit -memory trace

19.
Short term memory Can be enhanced by
• Attention/concentration
• Chunking
• Association
• Mnemonics

20.
Chunking
• Grouping the related information into ‘chunks’
• For example, chunking the phone numbers
• Ideal size for each ‘chunk’ is 3
• Basis for making good presentations

21.
INTERMEDIATE-LONG TERM MEMORY
• Temporary chemical or physical changes, or both, in either the synapse
presynaptic terminals or the synapse postsynaptic membrane, changes
that can persist for a few minutes up to several weeks
• When the sensory terminal is stimulated repeatedly but without
stimulation of the facilitator terminal, signal transmission at first is great,
but it becomes less and less intense with repeated stimulation until
transmission almost ceases. This phenomenon is habituation

22.
• If a noxious stimulus excites the facilitator terminal at the same time that the
sensory terminal is stimulated, instead of the transmitted signal into the
postsynaptic neuron becoming progressively weaker, the ease of
transmission becomes stronger and stronger.
• It will remain strong for minutes, hours, days, or, with more intense training,
up to about 3 weeks
• Even the noxious stimulus causes the memory pathway through the sensory
terminal to become facilitated for days or weeks thereafter

23.
Mechanism of facilitation (sensitization)
1.Release of serotonin from facilitator terminal
2.Activation of adenyl cyclase in sensory terminal
3.Formation of cAMP
4.Activation of protein kinase
5.Phosphorylation (blockage) of K+ Channels
6.Rise in intracellular voltage
7.Prolonged opening of Ca++channels
8.Enhanced Ca++entry in sensory terminal
9.Increased neurotransmitter release

24.
LONG TERM MEMORY

25.
Mechanisms involved
• Physical and structural changes in neurons- synaptic plasticity
• Increase in vesicle release sites
• Increase in number of transmitter vesicles released
• Increase in number of presynaptic terminals
• Changes in structures of the dendritic spines that permit
transmission of stronger signals
• Long term potentiation (LTP) and depression (LTD)
• Consolidation

26.
Formation of new dendritic spines and synapses

27.
Synaptic Plasticity
• Ability of synapses to undergo structural and/or physical changes in
response to sensory input
• Leads to change in synaptic strength (post synaptic response)
• Follows ‘use it or loose it’ phenomenon
• A process that underlies learning & memory
Enhancing your abilities is in your own hands because you can increase
or decrease the effectiveness of synapses which are the locus of
learning and memory

28.
The following important structural changes occur:
1. An increase in vesicle release sites for secretion of transmitter
substance
2. An increase in the number of transmitter vesicles released
3. An increase in the number of presynaptic terminals
4. Changes in structures of the dendritic spines tha permit transmission
of stronger signals
Thus, in several different ways, the structural capability of synapses to
transmit signals appears to increase during establishment of true long-
term memory traces

29.
LONG TERM POTENTIATION (LTP)
• Modifications take place as a result of increased use at a given
preexisting synapse that enhance the future ability of the presynaptic
neuron to excite the postsynaptic neuron.
• This connection gets stronger the more often it is used
• Prolonged increase in strength of existing synapse in response to high
frequency stimuli
• Can last for days or weeks (long enough for short term memory to be
consolidated)
• Especially prevalent in hippocampus
• Consolidates short term memory into long term

30.
AMPA NMDA

31.
Glutamate from pre synaptic terminal
AMDA receptor activation
Na+ entry into post synaptic terminal
Depolarization, EPSP generation
Increased EPSP moves Mg +2 out of NMDA receptor channel
Ca+2 enter post synaptic terminal

32.
Activates second messenger system which has 2 effects:
• Upregulates AMPA receptors on postsynaptic membrane
• Releases retrograde paracrine (NO) which enhances
glutamate release from presynaptic terminal

33.
Long term potentiation- Mechanism
• High levels of Ca+2 in post synaptic neuron
• Role of NMDA and AMPA receptors in postsynaptic membrane
• Activation of CaMKII (Ca+2-calmodulin dependent kinase II)

34.
Long term depression (opposite to LTP)
• Prolonged decrease in strength of existing synapse in response to low
frequency stimuli
• Can last for days or weeks
• Leads to negative memory

35.
Low levels of Ca+2
• Activation of phosphatase (instead of CaMKII)
• Dephosphorylation & closure of AMPA receptors
• Decreased number of AMPA receptors
• Decreased synaptic strength

36.
CONSOLIDATION of memory (declarative)
• Process by which short term memory is converted into long term
memory
• Hippocampus consolidates short term memory into long term
• Time required
5 to 10 minutes for minimum consolidation
1 hour for strong consolidation

37.
Factors affecting consolidation
• Rehearsal
• Factors decreasing brain alertness
Drowsiness
Depression/low mood
• Lack of interest
• Disorganized knowledge acquisition
• Brain concussion

38.
Codification process
• Comparison of new information for differences with the similar kind
of stored memory
• Only the differences (new files) are stored
• New information is stored with similar kind of old memory

39.
• Active & attentive mind consolidates in a better way
• Natural tendency of brain to rehearse the new information (LPT in
hippocampus)
• Consolidation weakens when feeling drowsy (caution for students)

40.
HIPPOCAMPUS
Part of limbic system
• Located on medial side of temporal lobe
• Stores new memories temporarily
• Consolidate new (short term memories) into long term memories
• In hippocampal lesion consolidation can’t occur

41.
Brain Areas Involved In Memory
• No single ‘memory center’
• Many areas involved
• Hippocampus, amygdala, other parts of limbic system, cerebellum,
prefrontal cortex, association areas
Working memory
Prefrontal cortex in frontal lobe
Short term memory/intermediate long term
Hippocampus, para hippocampus in medial temporal lobe

42.
Long term memory
Association areas of cerebral cortex (act like hard disk of computer)
Procedural memory
Motor cortex, cerebellum, basal ganglia

43.
AMNESIA -LOSS OF MEMORY (DECLARATIVE)
• Anterograde amnesia
Failure to establish new long term memories
Lesion in hippocampus (required to convert short term memories
into long term ones)
• No capability for storing verbal and symbolic types of memories
(declarative types of memory) in long-term memory or even in
intermediate memory lasting longer than a few minutes

44.
Retrograde amnesia
• Failure to recall past long term memories
• Lesion in hippocampus & thalamus
• Thalamus works like ‘windows search’
• Some degree of retrograde amnesia occurs along with anterograde
amnesia, which suggests that these two types of amnesia are at least
partially related and that hippocampal lesions can cause both

45.
Skill memory not affected
in hippocampus lesion