c 57 cortical centers, speech & memory
TRANSCRIPT
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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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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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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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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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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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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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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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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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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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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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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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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.