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Memory
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- 2. MEMORY Memory is theability to recall past events at the conscious or unconscious level.
- 3. INTRODUCTION The problemin discussing thoughts, memory, and learning is that we do not know the neural mechanisms of a thought and know little about the mechanisms of memory. Each thought certainly involves simultaneous signals in many portions of the cerebral cortex, thalamus, limbic system, and reticular formation of the brain stem. Some crude thoughts probably depend almost entirely on lower centers; eg. the thought of pain
- 7. Consciousness Consciousness canperhaps be described as our continuing stream of awareness of either our surroundings or our sequential thoughts.
- 8. Synaptic Facilitation &Synaptic Inhibition Memories are stored in the brain by changing the basic sensitivity of synaptic transmission between neurons as a result of previous neural activity & these are called memory traces. There importance is once the traces are established, they can be selectively activated by the thinking mind to reproduce the memories. Memory traces can occur at all levels of the nervous system.
- 10. Synaptic Facilitation & SynapticInhibition Long-term memories result from changed synaptic conduction in lower brain centers. However, most memory that we associate with intellectual processes is based on memory traces in the cerebral cortex.
- 11. Positive and NegativeMemory Our memories is recollections of previous thoughts or experiences & the greater share of are negative memories, not positive. Our brain is inundated with sensory information from all our senses. The brain has the capability to learn to ignore information that is of no consequence. i.e synaptic inhibition the resulting effect is called habituation. (negative memory).
- 13. Positive and NegativeMemory The information that causes important consequences such as pain or pleasure, the brain has a different automatic capability of enhancing and storing the memory traces. This is positive memory. It results from synaptic facilitation & called as memory sensitization. Special areas in the basal limbic regions of the brain determine whether information is important or unimportant and make the sub- conscious decision whether to store the thought as a sensitized memory trace or to suppress it.
- 14. Classification of Memories (1) Short-term memory which includes memories that last for seconds or at most minutes unless they are converted into longer-term memories. (2) Intermediate long-term memories, which last for days to weeks but then fade away. (3) Long-term memory, which can be recalled up to years or even a lifetime later.
- 15. WORKING MEMORY Inconnection with the prefrontal lobes another type of memory, called “Working memory,” that includes mainly short-term memory that is used during the course of intellectual reasoning but is terminated as each stage of the problem is resolved.
- 16. Classification of Memories Acc- to the type of information that is stored. Declarative memory basically means memory of the various details of an integrated thought, such as memory of an important experience that (1) memory of the surroundings, (2) memory of time relationships, (3) memory of causes of the experience, (4) memory of the meaning of the experience, (5) memory of one’s deductions that were left in the person’s mind.
- 17. Classification of Memories Skill memory is frequently associated with motor activities of the person’s body, such as all the skills developed for hitting a tennis ball, including automatic memories to (1) sight the ball, (2) calculate the relationship and speed of the ball to the racquet, (3) deduce rapidly the motions of the body, the arms, and the racquet required to hit the ball as desired—
- 18. SKILL MEMORY Allof these activated instantly based on previous learning of the game of tennis—then moving on to the next stroke of the game while forgetting the details of the previous stroke.
- 19. Short-Term Memory Short-termmemory is typified by one’s memory of 7 to 10 numerals in a telephone number for a few seconds to a few minutes at a time. Lasting till the person continues to think about the numbers or facts. A possible explanation of short- term memory is presynaptic facilitation or inhibition. At synapses that lie on terminal nerve fibrils immediately before these fibrils synapse with a subsequent neuron.
- 20. Short-Term Memory Theneurotransmitter chemicals secreted at such terminals frequently cause facilitation or inhibition lasting for seconds up to several minutes. Circuits of this type could lead to short-term memory.
- 21. Intermediate Long-Term Memory Intermediate long-term memories may last for many minutes or even weeks. They will eventually be lost unless the memory traces are activated enough to become more permanent. It can result from temporary chemical or physical changes, or both, that can persist for a few minutes up to several weeks.
- 22. Chemical Changes insnail
- 23. In thisfigure, there are two synaptic terminals. One terminal is from a sensory input neuron and terminates directly on the surface of the neuron that is to be stimulated; this is called the sensory terminal. The other terminal is a presynaptic ending that lies on the surface of the sensory terminal, and it is called the facilitator terminal. When the sensory terminal is stimulated repeatedly but without stimulation of the facilitator terminal, signal transmission at first is great, but it becomes less and less intense with repeated stimulation until transmission almost ceases. This phenomenon is habituation & is a type of negative memory
- 24. if anoxious stimulus excites the facilitator terminal at the same time that the sensory ter- minal is stimulated, Then the transmitted signal into the postsynaptic neuron becoming progressively stronger and stronger; and it will remain strong for minutes, hours, days, or, with more intense training, up to about 3 weeks even without further stimulation of the facilitator terminal. Thus, the noxious stimulus causes the memory pathway through the sensory terminal to become facilitated for days or weeks thereafter.
- 25. Molecular basis ofIntermediate Memory Mechanism for Habituation. At the molecular level, the habituation effect in the sensory terminal results from progressive closure of calcium channels through the terminal membrane. Mechanism for Facilitation. 1. Stimulation of the facilitator presynaptic terminal simultaneously with the sensory terminal causes serotonin release at the facilitator synapse on the surface of the sensory terminal.
- 26. 2.The serotoninacts on serotonin receptors in the sensory terminal membrane, and these receptors activate the enzyme adenyl cyclase inside the membrane & causes formation of cAMP. 3. The cyclic AMP activates a protein kinase that causes phosphorylation of a protein that itself is part of the K channels in the sensory synaptic terminal membrane & blocks the K channel conductance & can last for min- to several weeks. 4.This causes a greatly prolonged AP in the synaptic terminal because flow of K ions out of the terminal is necessary for rapid recovery.
- 27. 5. Theprolonged AP causes prolonged activation of the Ca channels, allowing tremendous quantities of calcium ions to enter the sensory synaptic terminal. These calcium ions cause greatly increased transmitter release by the synapse, thereby markedly facilitating synaptic transmission to the subsequent neuron.
- 29. Long-Term Memory Long-termmemory is generally believed to result from actual structural changes, instead of only chemical changes, at the synapses, and these enhance or suppress signal conduction. Structural Changes Occur in Synapses During the Development of Long-Term Memory. EM shows in invertebrate have demonstrated multiple physical structural changes in many synapses during development of long-term memory traces.
- 30. Long-Term Memory Themost important of the physical structural changes that occur are the following: 1. Increase in vesicle release sites for secretion of transmitter substance. 2. Increase in number of transmitter vesicles released. 3. Increase in number of presynaptic terminals. 4. Changes in structures of the dendritic spines that permit transmission of stronger signals. Number of Neurons and Their connectivities Often Change Significantly During Learning
- 32. Consolidation of Memory For short-term memory to be converted into long-term memory it must become “consolidated.” If short-term memory activated repeatedly will initiate chemical, physical, and anatomical changes in the synapses that are responsible for the long-term type of memory. 5 to 10 minutes for minimal consolidation. 1 hr. or more for strong consolidation. It can be explained by the phenomenon of rehearsal of the short-term memory.
- 33. Rehearsal The brainhas a natural tendency to rehearse newfound information, especially newfound information that catches the mind’s attention. This explains why a person can remember small amounts of information studied in depth far better than large amounts of information studied only superficially. It also explains why a person who is wide awake can consolidate memories far better than a person who is in a state of mental fatigue.
- 34. Codified The mostimportant features of consolidation is that new memories are codified into different classes of information. The new & old are compared for similarities and differences, & to store the information about these similarities and differences, rather than to store the new inform- unprocessed. Thus, during consolidation, the new memories are not stored randomly in the brain but are stored in direct ass. with other memories of the same type.
- 35. Role of SpecificParts of the Brain Hippocampus Promotes Storage of Memories— Anterograde Amnesia After Hippocampal Lesions. Retrograde Amnesia—Inability to Recall Memories from the Past. In some people who have hippocampal lesions, some degree of retrograde amnesia occurs along with anterograde amnesia, which suggests that these two types of amnesia are at least partially related and that hippocampal lesions can cause both.
- 36. Hippocampi AreNot Imp. in Reflexive Learning. People with hippocampal lesions usually do not have difficulty in learning physical skills. This type of learning is called skill learning or reflexive learning; it depends on physically repeating the required tasks over and over again, rather than on symbolical rehearsing in the mind.