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Definition

  • Neural plasticity – an adaptive response of the nervous system to experience and injury

Experience

  • Experiment with rats
    • Rats with an enriched environment have more synapses/dendrites/branching than animals in standard cages
    • The parts of the brain that are stimulated by the different parts of the enriched environment are improved by the particular environmental-based tasks that
    • Pyramidal neurons in the enriched house rats show more dendritic branching and more synapses relative to the pyramidal cells of a lab mouse
  • Experiment with sparrows
    • White-crowned sparrows – zonotrichia leucophrys gambelli and nutalli
      • Gambelli migrates 4300km each year
      • Nutalli is sedentary
    • We know that the hippocampus is involved in spatial memory, and we know that migrating birds have a high need for spatial memory
      • Hypothesis: gambelli will have a better spatial memory than nutalli and a larger hippocampus
    • Experimental:
      • Training – one trial associative memory learning task
        • Bird placed on perch and food in one of 5 feeders facing bird, given a 10 minute feed
      • Memory
        • Bird placed on perch and food in the same feeder, feeders facing away
      • Results
        • I – all birds went to the feeder with the food, shows all birds can see, can fly and are relaxed
        • II – gambelli inspected less feeders before finding the food
          • Therefore, gambelli has a better memory than nutalli
      • Brain measurements
        • Gambelli was found to have a greater hippocampus:total brain ratio than nutalli
        • Gambelli was found to have more neurons in the hippocampus than nutalli
          • Conclusion – size of hippocampus/memory/number of neurons in hippocampus is experience dependent
  • Taxi driver vs non-taxi driver experiment
    • London taxi drivers learn the map of London
      • Predicted neurological changes in the hippocampus
    • Experimental
      • MRI of 16 taxi drivers and 16 non-taxi drivers to find the volume of the hippocampus
        • No difference found
    • Experimental2
      • Anterior/middle/posterior parts of the hippocampus compared
        • Significant difference found:
          • The anterior was larger in the control
          • The posterior part was larger in the taxi drivers
        • Thus, concluded that spatial navigation skills resulted in grey matter redistribution
      • Alternate explanation – particular hippocampal arrangements predispose to taxi driving
      • Study poorly controlled: redistribution of hippocampal volume could be caused by other factors than spatial navigation.
    • Experimental3
      • Experience was found to be proportional to the posterior hippocampus volume and inversely proportional to the anterior hippocampus volume
      • Alternate explanation – stress, driving skills
    • Experimental4
      • Taxi drivers vs bus drivers (who have set routes and also high stress/long driving)
        • Bus drivers had larger anterior hippocampi
        • Taxi drivers had larger posterior hippocampi
  • Conclusion: spatial navigational skills is associated with redistribution of grey matter in hippocampus
  • Musicians vs non-musicians experiment
    • Amateur + professional had more grey matter than non-musicians
      • Especially in the motor, auditory, and visual-spatial areas



  • 2nd languages experiment
    • Proficiency in a second language increased the density of the language areas
  • Medical student experiment
    • Grey matter volume measured 3 months before exams, the day after the 3 months after
      • Found a significant increase in the grey matter
        • this also remained 3 months later
  • Summary – the hippocampus and cortical areas can be modified by stimulus and use

Injury

Rat/sugar experiment (see slides)

  • After stroke: Success is there (still gets the sugar), but the quality of the movement is different (less independent from the rest of the body - now it has to move its whole body just to move its arm)
  • After a stroke, there can be a limited degree of functional recovery
    • Due to:
      • Axonal sprouting
  • The adult cortex response to injury
  • Facilitated by:
    • Increased GAP43 – growth cone phosphoprotein
    • Decreased growth inhibition molecules – NogoA
    • Activation of growth - promoting genes
      • Neurogenesis
        • Waves of migrating neurons (neuroblasts) from the subventricular zone to areas of damage
    • Facilitated by cytokine erythropoietin (EPO)
  • Experiment language reorganisation
    • f-MRI
      • active neurons take up more oxygen, and thus have increased blood flow
      • fMRI can detect increased blood flow areas
    • Subjects: 14 right handed with aphasia, vs 14 right handed controls
      • Scanning:
        • Acute – 0-4 days after stroke
        • Subacute – 2 weeks afterwards at rehabilitation
        • Chronic – 4-12 months after stroke
      • Given a comprehension task, need to push a button when the sentence was incorrect
    • Results
      • Normal people
        • When contrasting sentences – decision-making areas of the brain are activated (frontal cortex)
        • When pushing the button – motor areas
        • When comprehending – Wernicke’s and Broca’s areas
      • Acute – little activation, some in Broca’s area
      • Subacute – Broca homologue region on the right side activated; also some return of the function of left hemisphere
        • Language improvement
      • Chronic – looks normal
    • Progress of recovery
      • Reduced left side
      • recruitment of right side
      • normalisation and consolidation of language system