neurophysiology mechanism and sciences for memory --> registration, encoding, consolidation and retrieval

1. NEUROPHYSIOLOGY
OF MEMORY
o Dr. Sujoy Kabiraj (1stYear Neuromedicine Resident, BIN)
o Chairperson: Dr. Adreesh Mukherjee, Assistant Professor, BIN

2. INTRODUCTION
 Memory is essential to all our
lives.Without a memory of the
past, we cannot operate in the
present or think about the
future. We would not be able to
remember what we did
yesterday, what we have done
today or what we plan to do
tomorrow. Without memory,
we could not learn anything.
 Memory is involved in
processing vast amounts of
information.This information
takes many different forms, e.g.
images, sounds or meaning.

3. DEFINITION
 Memory is the faculty of the brain by which data or information is
encoded, stored, and retrieved when needed. It is the retention of
information over time for the purpose of influencing future
action. If past events could not be remembered, it would be
impossible for language, relationships, or personal identity to
develop.
 Memory loss is usually described as forgetfulness or amnesia.
doi:10.3389/fpsyg.2012.00403. PMC 3485580. PMID 23125838

4. 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 50bit/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.

5. MEMORY

6. TYPESOF
MEMORY
 There are 4 different types of memory:
 Sensory memory (immediate memory)
 Primary memory (short term memory)
 Secondary memory (long term
memory)
 Tertiary memory (permanent memory)

7. TYPESOF
MEMORY

8. SENSORY
MEMORY
 Sensory memory holds information, derived from the senses, less
than one second after an item is perceived.
 The ability to look at an item and remember what it looked like
with just a split second of observation, or memorization, is the
example of sensory memory.

9. TYPESOF
SENSORY
MEMORY
 Three types of sensory memories exist.
 Iconic memory is a fast decaying store of visual information, a
type of sensory memory that briefly stores an image that has been
perceived for a small duration.
 Echoic memory is a fast decaying store of auditory
information, also a sensory memory that briefly stores sounds that
have been perceived for short durations.
 Haptic memory is a type of sensory memory that represents a
database for touch stimuli.
ISBN 978-0-205-68557-8. OCLC 268547522

10. MECANISM
OFACTION
 Stimulation of reverberating circuits – repeated activation of
neurons.
 Synaptic sensitization – if sensory experience coupled with painful
stimuli.
 Posttetanic potentiation – multiple stimuli at presynaptic terminal
→↑ Ca content in presynaptic terminal →↑ release of
neurotransmitters.

11. MECHANISM
OF
FORGETTING
 Fading (spontaneous
and gradual decline in
the amount of
information)
 Extinction
(spontaneous
Disappearance of
information from
memory)

12. SHORT-TERM
MEMORY
 Short-term memory is also known as working memory.
 Short-term memory allows recall for a period of several seconds to
a minute without rehearsal.
 Its capacity, however, is very limited.

13. 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
doi:10.1017/S0140525X01003922. PMID 11515286. S2CID 8739159.

14. 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
 Long term potentiation of synapses
 Changes in physical properties of postsynaptic
membrane → ↑ sensitivity to chemical transmitters
 Mechanism of forgetting: New information replaces old

15. Working
Memory Model
(WMM)
• Baddeley &
Hitch (1974)

16. A simplified depiction
(adapted from the
multicomponent
working memory
modelby Baddeley,
2010) as implicated in
the brain.ACC,
Anterior cingulate
cortex.

17. LONG-TERM
MEMORY
 The storage in sensory memory and short-term memory generally
has a strictly limited capacity and duration
 By contrast, long-term memory can store much larger quantities
of information for potentially unlimited duration (sometimes a
whole life span).
 Its capacity is immeasurable.

18. LONG-TERM
MEMORY
 Duration: (hours to years )
 Entry into storage:
 Stimulation of the reward or punishment systems.
 Repeated practice or rehearsal of the experience.
 Recall or access to storage: slow

19. MECHANISM
 Made by formation of memory engrams (long- lasting memory
traces) formed by structural changes in presynaptic terminals
 Memory engrams made up by;
 Increase in number of vesicles
 Increase in number of presynaptic terminals
 Increase in release sites of chemical transmitters
 Generation of new receptor sites
 Long term potentiation
 Engrams remain for long time up to several years
 Formation of new engrams requires protein synthesis

20. MECHANISM
OF
FORGETTING
 Proactive inhibition
 If the old information
repels the new one
 Retroactive inhibition
 If the new information
replaces the old one

21. 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

22. PHYSIOLOGY
OF MEMORY
 Neurons are the basic means of information transfer within the
nervous system.
 Information in the form of a stimulus is detected by a specific type of
neuron (sensory neuron).
 The information is then passed to an adjacent neuron (interconnecting
neuron) and so on till it gets to where it’s going in the brain.
 It is an electro-chemical process that allows this to happen.

24. TYPESOF
NEURONS
 Sensory Neurons: These detect the stimulus from each of the
senses and communicate the information to the interconnecting
neurons.
 Interconnecting Neurons: These transfer information
throughout the nervous system and also connect to the motor
neurons.
 Motor Neurons: These connect to and activate muscle tissue.

25. HOW
INFORMATION
IS MOVED
 All stimulus or nerve messages are picked up by the dendrites
protruding from the cell body.
 When the stimulus is strong enough, the cell body fires an
electrical impulse.
 An electrical impulse travels down the axon or “outgoing branch”.
Then the axon terminals and buds at the end are stimulated to
release chemicals called neurotransmitters (tiny molecules that
send specific messages).

26. HOW
INFORMATION
IS MOVED

27. HOW
INFORMATION
IS MOVED
 Neurotransmitters are chemicals that are used to relay, amplify
and modulate signals between a neuron and another cell.
 The dendrites or “incoming branches” of other neurons pick up
these chemicals as they cross the synapse.
 The synapse is the space between the buds of one neuron and
dendrites of the adjacent neuron.
 What it comes down to is brain cells, or neurons, communicating
with each other through electro-chemical pathways.

28. NEURON
SHOWINGTHE
TRANSFEROF
NEUROTRANS-
MITTERSAT
THESYNAPSE

29. HOW BRAIN
HELP IN
MEMORIZATION
 Memory formation and storage involves many parts of the brain at
the same time.
 The brain is made up of four main regions which include the
cerebrum, the cerebellum, the limbic system, and the brain stem.

30. HOW BRAIN
HELP IN
MEMORIZATION
 The cerebrum is the largest, most recently evolved and most
developed part of the brain and is made up of two hemispheres
(the right and left) and four types of lobes (frontal, occipital,
temporal, and parietal).
 The frontal lobes are involved in thinking, organization,
short-term memory and problem-solving.
 The occipital lobes process images a person sees and links
them with ones that have been stored in the memory.
 The temporal lobes process sensory information such as
temperature, touch, smell, taste and sound and are also
involved in the storage of memories.
 The parietal lobes also process sensory information.
 The outermost layer of the cerebrum, the cerebral cortex, plays a
role in higher brain functions such as memory and language.

31. FORMING,
STORING
AND
RECALLING
MEMORIES
 Memories are stored within groups of interconnected nerve cells
referred to as assemblies that are triggered together on exposure
to a stimulus, such as the smell of a certain food or hearing a
friend’s voice.
 The greater the number of nerve cells that fire simultaneously, the
stronger the interconnection within an assembly.
 How active such cells are within an assembly is thought to
determine the memory experienced, but researchers are still
investigating this process.
https://www.britannica.com/science/human-nervous-system/Memory

32. STAGESOF
MEMORY

33. MEMORY
CONSOLIDATION
 it is a category of processes that stabilize a memory trace after its
initial acquisition.
 A memory trace is a change in the nervous system caused by
memorizing something.
 Consolidation is distinguished into two specific processes.The
first, synaptic consolidation, which is thought to correspond
to late-phase long-term potentiation.

34. MEMORY
CONSOLIDATION
 The second process is systems consolidation, occurring on a
much larger scale in the brain, rendering hippocampus-
dependent memories independent of the hippocampus over a
period of weeks to years.
 Recently, a third process has become the focus of
research, reconsolidation, in which previously consolidated
memories can be made labile again through reactivation of the
memory trace.

35. MEMORY
ENCODING
 When information comes into our memory system (from sensory
input), it needs to be changed into a form that the system can
cope with, so that it can be stored.
 Think of this as similar to changing your money into a different
currency when you travel from one country to another. For
example, a word which is seen (in a book) may be stored if it is
changed (encoded) into a sound or a meaning (i.e. semantic
processing).

36. MEMORY
ENCODING
There are three main ways in which information
can be encoded (changed):
1.Visual (picture)
2. Acoustic (sound)
3. Semantic (meaning)
For example, how do you remember a telephone number you have looked
up in the phone book? If you can see it then you are using visual coding,
but if you are repeating it to yourself you are using acoustic coding (by
sound).

37. MEMORY
STORAGE
 This concerns the nature of memory stores, i.e., where the
information is stored, how long the memory lasts for (duration), how
much can be stored at any time (capacity) and what kind of
information is held.
 The way we store information affects the way we retrieve it. There
has been a significant amount of research regarding the differences
between ShortTerm Memory (STM ) and LongTerm Memory (LTM).

38. MEMORY
STORAGE

39. MEMORY
RETRIEVAL
 This refers to getting information out storage. If we can’t
remember something, it may be because we are unable to retrieve
it. When we are asked to retrieve something from memory, the
differences between STM and LTM become very clear.
 STM is stored and retrieved sequentially. For example, if a group
of participants are given a list of words to remember, and then
asked to recall the fourth word on the list, participants go through
the list in the order they heard it in order to retrieve the
information.
 LTM is stored and retrieved by association. This is why you can
remember what you went upstairs for if you go back to the room
where you first thought about it.