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Mechanisms of Learning and Memory

Mechanisms of Learning and Memory. Lecture 3. Memory as psychical function.

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Mechanisms of Learning and Memory

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  1. Mechanisms of Learning and Memory Lecture 3

  2. Memory as psychical function • 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.

  3. Nerve substrate of memory • 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.

  4. Physiological mechanisms of memory • 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.

  5. Thinking process as psychical function • 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 right-handed 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.

  6. Short term memory • 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, cued-recall, and delayed cued-recall. Your results will be compared to Sperling’s finding of rapid decay of the visual “icon.”

  7. Long term memory • 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.

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