Download Mechanisms of Learning and Memory

Mechanisms of Learning
and Memory
Lecture 3
Memory as psychical function
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Memory function helps fixing of perceived information,
keeping it in verbal form or as traces of percept stimuli and
recognizing of this information in proper time. Genetic
memory keeps information about body structure and forms
of its behavior. Biological memory is presented in both
philogenetic and ontogenetic forms. The immune memory
and psychical memory for instance, belong to ontogenetic
memory.
General characteristics of memory are duration, strength of
keeping the information and exactness of its recognizing. In
man mechanisms of perception and keeping the information
are developed better, comparing to other mammalians.
According to duration is concerned short-time and long-time
memory; in relation to kind of information – sensory and
logic.
Nerve substrate of memory
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It’s discovered the nervous substrate of long-term
memory is mostly cerebral cortex. The most
important regions are temporal lobes, prefrontal area
and hippocampus. Experimental researches revealed
that some thalamic nuclei and reticular formation take
part in memory function.
Reticular formation gives ascending stimulatory
influences to cerebral cortex, which help in keeping
awake condition of cortex and provides voluntary
attention.
Physiological mechanisms of memory
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At the molecular level, the habitation effect in the sensory
terminal results from progressive closure of calcium channels
through the presynaptic terminal membrane.
In case of facilitation, the molecular mechanism is believed to be
following. Facilitated synapse releases serotonin that activates
adenylyl cyclase in postsynaptic cell. Then cyclic AMP activates
proteinkinase that then causes phosphorylation of proteins. This
blocks potassium channels for minutes or even weeks. Lack of
potassium causes prolonged action potential in the presynaptic
terminal that leads to activation of calcium pores, allowing
tremendous quantities of calcium ions to enter the sensory
terminal. This causes greatly increased transmitter release,
thereby markedly facilitating synaptic transmission.
Thus in a very indirect way, the associative effect of stimulation
the facilitator neuron at the same time that the sensory neuron is
stimulated causes prolonged increase in excitatory sensitivity of
the sensory terminal, and this establishes the memory trace.
Thinking process as psychical function
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The prefrontal association area is essential to carrying out thought
processes in the mind. This presumably results from some of the
same capabilities of the prefrontal cortex that allow it to plan
motor activities.
The prefrontal association area is frequently described as
important for elaboration of thoughts to store on a short-term basis
“working memories” that are used to analyze each new thought
while it is entering the braine. The somatic, visual, and auditory
association areas all meet one another in the posterior part of the
superior temporal lobe. This area is especially highly developed in
the dominant side of the brain – the left side in almost all righthanded people.
It plays the greatest single role of any part of cerebral cortex in the
higher comprehensive levels of brain function that we call
intelligence. This zone is also called general interpretative area,
the gnostic area, the knowing area, tertiary association area. It is
best known as Wernike’s area in honor of the neurologist who first
describes it.
Short term memory
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Eric Kandel showed initially that weaker stimuli give rise to a
form of short term memory, which lasts from minutes to
hours. The mechanism for this "short term memory" is that
particular ion channels are affected in such a manner that
more calcium ions will enter the nerve terminal.
This leads to an increased amount of transmitter release at the
synapse, and thereby to an amplification of the reflex. This
change is due to a phosphorylation of certain ion channel
proteins, that is utilizing the molecular mechanism described
by Paul Greengard.
Sperling’s classic experiments on the duration of visual
sensory memory simulate Iconic Memory. You will see nine
random letters flashed in a 3 x 3 matrix, and will attempt to
recall the letters under three conditions: free-recall, cuedrecall, and delayed cued-recall. Your results will be compared
to Sperling’s finding of rapid decay of the visual “icon.”
Long term memory
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A more powerful and long lasting stimulus will result in a
form of long term memory that can remain for weeks. The
stronger stimulus will give rise to increased levels of the
messenger molecule cAMP and thereby protein kinase A.
These signals will reach the cell nucleus and cause a change
in a number of proteins in the synapse. The formation of
certain proteins will increase, while others will decrease. The
final result is that the shape of the synapse can increase and
thereby create a long lasting increase of synaptic function.
In contrast to short term memory, long term memory requires
that new proteins are formed. If this synthesis of new
proteins is prevented, the long term memory will be blocked
but not the short term memory.