c 57 cortical centers, speech & memory

8/6/2019 c 57 Cortical Centers, Speech & Memory

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C 57Cortical Centers, Speech &

Memory

By

Prof. Dr. Abdul Majid

MBBS, M.Phil, FCPS


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Memories

Memories are the storage of sensory

information in all parts of the brain

especially in the synapses. It occurs dueto facilitation or inhibition of the memory

traces.

Positive memory:

For incoming information that causes

important consequences such as pain

or pleasure,


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Cont:

the brain has automatic capability of enhancing

and storing the memory traces. This is positive

memory. It results from facilitation of the

synaptic pathways, and process is calledmemory sensitization.

Negative memory:

The brain has the capability to ignore theinformation that is of no consequent. This

occurs by inhibition of the synaptic

transmission and the process is called

habituation or negative memory.


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Cont:

This occurs by inhibition of the synaptic

transmission and the process is called

habituation or negative memory.The role of limbic system:

Special areas in the limbic regions of the

brain determine whether information is

important or unimportant and make the

subconscious decision whether to store

the thoughts as sensitized memory or to

suppress it.


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Cont:

Classification of the memories:

According to the type of information that

is stored.1. Declarative memory:

It includes all description regarding an

event or incident.

2. Skill memory:

It includes capability of a person after

training that how he will play Tanis ball.


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Cont:

Classification of the memories:

According to the time for which they are

remembered.1. Short term memories.

2. Intermediate long term memories.

3. Long term memories.


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Cont:

Short term memories:

Includes memories that last for seconds

to minutes unless they are converted intolong term memories. It is typified by ones

memory of 7 to 10 numerals in a

telephone number (or 7 to 10 other

discrete facts) for a few seconds to a fewminutes at a time but lasting only as long

as the person continues to think about

the numbers or facts.


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Cont:

Short term memory is caused by

continual neural activity resulting from

signals that travel around & around a

temporary memory trace in a circuit of

reverberatory neurons.

Other possibility is that it may occur by

presynaptic facilitation or inhibition.


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Cont:

Intermediate long term memories:

It may last for many days to weeks. They

will eventually be lost unless thememories traces are activated enough to

become more permanent. They result

from temporary chemical or physical

changes or both in either the presynapticterminals or postsynaptic membrane.


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Memory System that has been

Discovered in the Snails Aplysia


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Cont:

When the sensory terminal is stimulated

repeatedly but without stimulation of the

facilitated terminal, the signal

transmission at first is greater, but it

becomes less & less intense with

repeated stimulation until transmission

almost ceases. The neuronal circuit tolose its response to repeated events that

are insignificant.


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Cont:

Conversely, if the noxious stimulus

excites the facilitated terminal at the

same time that the sensory terminal is

stimulated, then transmission of signal

instead of becoming weaker & weaker

becomes stronger & stronger, and it will

remains stronger for days upto 3weekseven without further stimulation of

facilitated terminal.


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Cont:

Molecular basis of intermediatememory:

Mechanism of habituation, it occurs dueto progressive closure of calciumchannels.

Mechanism of facilitation:

1. Stimulation of facilitator presynapticterminal releases serotonin.

2. Serotonin activates adenyl cyclaseresulting in formation of cAMP.


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Cont:

3. cAMP activates protein kinase that

causes phosphorylation of a protein that

itself is part of potassium channels in

the sensory synaptic terminal

membrane, this in turn blocks the

channels for potassium conductance.

(The blockage can last for minutes uptoseveral weeks).


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Cont:

4. Lack of potassium conductance causes

greatly prolong AP in the synaptic

terminal.

5. The prolonged AP causes prolonged

activation of calcium channels which

enter into the sensory terminal resulting

in release of neuro transmitter.


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Cont:

Long term memory:

it is the type of memory, which, once

stored, can be recalled upto years oreven a life time later. It is believed to

result from actual structural changes,

instead of only chemical changes, at the

synapses and these changes enhance orsuppress the signal transmission.


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Cont:

These physical structural changes will

not occur if the drug is given that blocks

DNA stimulation of protein replication in

the presynaptic neuron physical

structural changes include;

Increased in vesicle release sites.

Increased in the number of transmitter

vesicles released.


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Cont:

Increased in the number of presynaptic

terminals.

C

hanges in the structure of the dendriticspines that permit transmission of

stronger signals.

Consolidation of memory:

For short term memory to be changed

into long term memory it must be

consolidated short term memory if

activated repeatedly will initiate


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Cont:

chemical physical and anatomical

changes in the synapses that are

responsible for long term memory.

The process requires 5-10 minutes for

minimal consolidation and 1 or more

hours for strong consolidation e.g. if

strong sensory impression is made onthe brain but is immediately followed by;


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Cont:

Electrical convulsions.

Brain concussion.

Sudden application of generalanesthesia then consolidation is

prevented.

Rehearsal enhances the process ofconsolidation. Also a person who is wide

awake can consolidate better than a

person who is in a state of mental

fatigue.


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Cont:

Role hippocampi:

Destruction of hippocampus can result in

to anterograde amnesia (loss of shortterm memory) or some retrograde

amnesia (loss of memory of the past) or

both. Damage to certain areas of the

thalamus certainly causes retrogradeamnesia. Hippocampi are not essential

for skill learning or reflexive learning.

c 57 cortical centers, speech & memory

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