Physiology of memory and learning

Physiology of memory and learning

1. MEMORYMEMORY
BY
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2. MemoryMemory
Def
It is the ability of the brain to store information and recall it
at later time
Capacity of the brain:
It is limited (total capacity of brain is 3x 10
8
bits)
So, informations entering brain are either;
A.Selected and stored (1%) → most important
B.Other (99%) → are neglected and forgotten

3. MemoryMemory
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

4. MemoryMemory
Types of memory:
There are four different types of memory:
[I] SENSORY MEMORY (Immediate memory).
[II] PRIMARY MEMORY (Short-term memory)
[III] SECONDARY MEMORY (Long-term memory)
[IV] TERTIARY MEMORY (permanent memory)

5. 11. . Sensory MemorySensory 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

6. 11. . Sensory MemorySensory 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)

7. 2. Short-term Memory2. 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

8. 2. Short-term Memory2. 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

9. 3. Long-term Memory3. Long-term Memory
Duration: (hours to years )
Capacity
–Very large
–Information stored according to its significance
Entry into storage: 1. Stimulation of the reward or
punishment systems.
2. Repeated practice or rehearsal of the experience.
Recall or access to storage: slow
Mechanism:
Made by formation of memory engrams (long-
lasting memory traces) formed by structural
changes in presynaptic terminals

10. 3. Long-term Memory3. 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

11. 3. Long-term Memory3. Long-term Memory
Mechanism of forgetting:
Proactive inhibition : If the old information repels the
new one
Retroactive inhibition: If the new information
replaces the old one

13. 4. Permanent Memory4. 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

15. Phases of memoryPhases of memory
Consolidation-converting the encoded information into a
form that can be permanently stored. The hippocampal and
surrounding areas apparently accomplish this.
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.
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.


16. Consolidation of memoryConsolidation of memory
It means the process of conversion
of STM to LTM
It takes from 5 min to 2 hrs
It is interrupted by
1.Deep anaesthesia
2.Brain concussion
3.Electroconvulsive therapy

17. Brain Regions involved in Consolidation of Brain Regions involved in Consolidation of
memorymemory
•Hippocampus
•Anterior & lateral
temporal lobe,
•Medial temporal lobe
•Amygdala

18. Hippocampus and Consolidation of memoryHippocampus 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

20. Encoding of memoryEncoding 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

21. Encoding of memoryEncoding of memory
Hippocampus
store
Mamillary
body
Orbitofrontal
cortex
Basal forebrain
Meynerts Nucleus
Amygdala
store
(Temporal lobe)
Neocortex
store
All bits
Select important informations
(reward or punishment)
Cholinergic projections
Cholinergic projections
Cholinergic projections

22. Disorders of MemoryDisorders 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.
•It usually follows a traumatic event that interferes with the
normal activity of the brain, such as a strong brain
concussion and vascular strokes

23. Disorders of MemoryDisorders 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

24. Disorders of MemoryDisorders 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

25. THANKS
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