Pp 14 Neuro Memory Systems


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Pp 14 Neuro Memory Systems

  1. 1. Neurology of Memory Systems
  2. 2. Review <ul><li>Conditioning </li></ul><ul><ul><li>Habituation/Sensitization </li></ul></ul><ul><li>Working Memory </li></ul><ul><ul><li>Phonologic </li></ul></ul><ul><ul><li>Visual/Spatial Sketchpad </li></ul></ul><ul><ul><li>Central Executive </li></ul></ul><ul><li>Long-Term-Memory </li></ul><ul><ul><li>Implicit </li></ul></ul><ul><ul><li>Explicit </li></ul></ul>
  3. 3. Brain Systems Conditioning
  4. 4. The Aplysia <ul><li>Also called a sea slug </li></ul><ul><li>It is a mollusk with nervous system containing only about 5000 neurons </li></ul><ul><li>Has specific reflexes: touching the animal causes the gill to be pulled inward </li></ul><ul><li>This animal has made it easy to study the basic neural systems of learning </li></ul>
  5. 5. Habituation <ul><li>Due to Synaptic Depression </li></ul><ul><li>There is a decrease in the release of neurotransmitter </li></ul><ul><li>The transmitter is not used up but rather the the repeated stimulation causes a change in the ion flow which would normally trigger the transmitter to be released </li></ul>
  6. 6. Picture
  7. 7. Sensitization <ul><li>Occurs at the same synapse but by the actions of another neuron terminal (interneuron) </li></ul><ul><li>A shock to the tail activates the release of a (stimulant) neurotransmitter that causes the terminal to change the flow of ions </li></ul><ul><li>This time the change in ions causes more neurotransmitter to be released </li></ul>
  8. 8. Picture
  9. 9. Duration <ul><li>A single training session of 10 touches give rise to learning that lasts minutes (STM-LTP and no protein) </li></ul><ul><li>Four training sessions of 10 trials a day (spaced over four days) give rise to learning that lasts at least three weeks (LTM-requires protein synthesis) </li></ul><ul><li>Overall it seems that learning takes places relatively quickly </li></ul>
  10. 10. Conditioning of Fear <ul><li>Typically a shock will be used to evoke a fear response (increased heart rate) </li></ul><ul><li>A small lesion was made in the hypothalamus (believed to be involved in the control of the cardiovascular system) </li></ul><ul><li>There was no longer an increase in heart rate due to the tone. There was still an increase in heart rate due to shock </li></ul><ul><li>The behavior stayed the same, but the physiological learned fear response no longer existed </li></ul><ul><li>Amygdala projects to the hypothalamus </li></ul>
  11. 11. Conditioning Motor Response <ul><li>Eyeblink conditioning involves a learned motor response </li></ul><ul><li>A small lesion in the cerebellum abolishes the learning and memory of a conditioned motor response </li></ul><ul><li>Is the memory actually stored there? Yes!! </li></ul><ul><li>This is the only long-term memory trace that has been localized in the mammalian brain </li></ul>
  12. 12. Brain Systems Working memory
  13. 13. Visual Sketchpad and the Brain <ul><li>Monkey learned a STM task where the food was under the new object </li></ul><ul><li>Lesions of the hippocampus disrupted STM of what they had seen and they could not tell the difference between old and new object </li></ul><ul><li>They could discriminate between objects, so visual perception was intact </li></ul>
  14. 14. Spatial Sketchpad and the Brain <ul><li>Monkey learned a spatial STM task </li></ul><ul><li>Destruction of a region of frontal cortex severely disrupts the ability to perform the task </li></ul><ul><li>The monkey can still perform the visual STM task </li></ul>
  15. 15. Continuous Brain Activity <ul><li>Monkeys were trained to remember a color for 16 seconds (the temporal lobe activated during color perception) </li></ul><ul><li>Recording brain activity showed that during the 16 sec, there was continuous activity in the temporal lobe </li></ul><ul><li>Continuous activity has also been found during remembering tasks in other sensory areas of the brain </li></ul>
  16. 16. Frontal Lobe <ul><li>The frontal lobe is also continuously active during a remembering task </li></ul><ul><li>It is possible to disrupt the continuous activity in (say) the temporal lobe during a color remembering task, but continuous activity in the frontal lobe remains continuous </li></ul><ul><li>This is neurologic evidence that the frontal lobes have executive control over other processing systems </li></ul>
  17. 17. Memory Systems Long-Term-Memory
  18. 18. LTM & STM Storage Areas <ul><li>How do the short-term and long-term forms of memory relate to each other, and do they occur at the same or different locations? </li></ul><ul><li>It seems that short-term learning results in connections simply being depressed or stimulated. Long-term learning involves inactivation or forming of new connections </li></ul><ul><li>Thus, the same synaptic connections that are used in a STM are also used in a LTM </li></ul>
  19. 19. Medial Temporal Lobe <ul><li>This structure seems to be the gateway into LTM from STM </li></ul><ul><li>However, the structure is not the repository of LTM </li></ul><ul><li>LTMs are thought to be stored in the same distributed set of structures that perceive, process, and analyze what is to be remembered </li></ul>
  20. 20. LTM Storage Areas <ul><li>Activity in the inferior temporal lobe was recorded while monkeys viewed visual patterns. Found that specific neurons responded best to specific pictures </li></ul><ul><li>Monkeys learned 12 picture pairs </li></ul><ul><li>Before one neuron responded to one picture. After learning, a neuron responded to the original picture and the picture that was paired with it </li></ul>
  21. 21. Hippocampal Damage <ul><li>Damage to the hippocampal system not only impairs new learning but also can disrupt recent memory </li></ul><ul><li>Thus, memory is not fixed at the time of learning but takes time to develop a permanent form </li></ul>
  22. 22. Establishing LTM <ul><li>Memory does not start in the hippocampus and diffuse out to the cortical areas, but rather is always in the cortex </li></ul><ul><li>The medial temporal lobe stores some aspect of the information for a significant period after learning </li></ul><ul><li>One idea is that the medial temporal lobe stores links or pointers that connect multiple cortical areas </li></ul>
  23. 23. Implicit/Explicit and the Brain <ul><li>Using PET, brain activity was recorded during implicit and explicit memory tasks </li></ul><ul><li>Subjects learned a list of words: In the explicit condition, they had to remember the words during the 40 sec scan. In the implicit condition a word stem completion task was used </li></ul><ul><li>In the explicit test there was more activity in the hippocampus, but in the implicit test there was more activity in the visual areas </li></ul><ul><li>Thus, implicit and explicit memory seem to be in different brain regions </li></ul>
  24. 24. Memory Systems The Adaptable Neuron
  25. 25. LTP <ul><li>The process that lead to long-term changes in the neuron is called long-term-potentiation (LTP) </li></ul><ul><li>Found in the lab when a brief high-frequency period of electrical activity was applied artificially to pathways in the hippocampus </li></ul><ul><li>The result was an increase in “synaptic strength” lasting for days or weeks (depending) </li></ul>
  26. 26. How Do LTPs Work? <ul><li>It is very complicated and it dose not work the same in all regions of the brain </li></ul><ul><li>LTP is associated with an increased probability that neurotransmitters will be released </li></ul><ul><li>Oddly enough, increasing the probability of neurotransmitter release results from a chemical message (nitric oxide?) sent from the post-synaptic nerve terminal </li></ul>
  27. 27. Need More Than LTP to Make a Long-Term-Memory --Protein <ul><li>The switch from STM to LTM is complicated </li></ul><ul><li>Communication between neurons will trigger special a regulatory protein that regulates gene (DNA) expression in the nucleus of the neuron </li></ul><ul><li>DNA produce new proteins that add to the physical structure of the neuron </li></ul>
  28. 28. Growing New Synapses <ul><li>Protein production builds new synapses between neurons </li></ul><ul><li>As time passes and there is no further use of the synapses the new synaptic terminals are lost </li></ul>