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Evolución y desarrollo cerebral durante el aprendizaje. Timothy De Voogd.


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Evolución y desarrollo cerebral durante el aprendizaje. Timothy De Voogd.

  1. 1. Learning in Birds-- And how it relates to learning in us. Timothy DeVoogd Cornell University (Attempting to catch birds for research)
  2. 2. My own initial rationale was simple curiosity about brain function and brain plasticity (and I had become allergic to rats in grad school) . I assumed some sort of similarity to humans, without thinking much about why this would be or how it would have arisen. Why Study Birds?
  3. 3. Because what we learn can show us what our brains might do: birds as “ a model system” for human biology. But what do you tell NIH or Colciencias (“Health Relevance”), or your cousins (“Tim, are you still studying bird brains” [muted laughter])
  4. 4. Model System <ul><li>If we’re honest, this seems unlikely: </li></ul><ul><ul><li>Birds are not closely related to us </li></ul></ul><ul><ul><li>Their brains are very different </li></ul></ul><ul><ul><ul><li>(nothing that looks like cortex </li></ul></ul></ul><ul><ul><ul><li>No corpus callosum </li></ul></ul></ul><ul><ul><ul><li>Different layout (and names!) of other regions </li></ul></ul></ul><ul><ul><li>Their activities also seem too different </li></ul></ul>
  5. 5. Bird Song Learning “ How does a bird’s brain learn song? Spatial Learning “ How do birds remember places?”
  6. 6. Baby Songbirds are Altricial at Hatching
  7. 7. Songs of Normally Reared Sparrows
  8. 8. Songs of Sparrows Reared in Isolation
  9. 9. 1. In most songbirds, males do all or most of the singing. Females sing little or not at all. 2. Young males learn their songs from adult males 3. As adults, males of many species attract females with song 4. Singing occurs with reproduction For many species outside of the tropics, this is seasonal 5. Different species vary in how complex a song they typically sing 6. For all species but those with the simplest song types, males within a species also differ in song complexity Song Facts
  10. 10. Causation <ul><li>Determine the physical structures that produce song </li></ul><ul><ul><li>Syrinx, at the opening of two bronchi </li></ul></ul><ul><ul><li>Beak and tongue movements </li></ul></ul><ul><li>Map how the brain controls these </li></ul><ul><ul><li>Songbird song is produced using the motor song system, a group of brain regions that are highly interconnected. </li></ul></ul><ul><li>Map correlations between brain structure and function </li></ul><ul><ul><li>Across sexes and seasons </li></ul></ul><ul><ul><li>Between and within species </li></ul></ul>
  11. 11. The Motor Song System consists of Production (red) and Regulatory Nuclei (blue) [No obvious correspondence to mammal forebrain in general layout or in specific structures] Red paths: for production Blue: originally unknown,
  12. 12. Relations to Learning <ul><li>HVC and RA are essential for song production . Could they be involved in the learning ? Our approaches: </li></ul><ul><ul><li>A. Comparative study across species </li></ul></ul><ul><ul><li>B. Study of variation within species </li></ul></ul><ul><ul><li>C. Experimental manipulation of opportunity to learn </li></ul></ul>
  13. 13. DeVoogd, Székely & Büki-- part of the Hungarian work crew
  14. 14. HVC / RA Predicts Learning Ability
  15. 15. Comparisons across more closely related clades (groups of species) yields better comparability
  16. 16. Syllable Repertoire can Vary by Nearly Two Orders of Magnitude Between Warbler Species
  17. 17. HVC HVC Marsh Warbler River Warbler Differences in HVC Volume Between Species can be Striking-- And they parallel song complexity Székely et al., ‘96
  18. 18. Airey & DeVoogd, ‘00 B. Variation Within a Species: HVC Volume and Repertoire Size are Positively Correlated in Zebra Finches -2 0 2 -0.075 0.000 0.075 Relative HVC Volume Relative Repertoire Size r = 0.52, p < .02
  19. 19. Volumes of brain areas may be poor measures of processing capacity--the actual job of the brain. This may be more closely estimated by assessing cell number, and integrating this with axonal, dendritic and synaptic distribution (i.e. connection information)
  20. 20. Song System: Golgi Stained RA Neurons RA [Not like cortical neurons]
  21. 21. C. Manipulate Opportunity to Learn: Male Zebra Finches Reared in Isolation Have Abnormally Simple Song and Fewer Spine Synapses in HVC Lauay, Komorowski & DeVoogd, 2005 0 5 10 15 20 25 30 Social Deprived Isolate Number of Spines / 12µm of Dendrite p < .05
  22. 22. Song is interactive: Accurate decoding is as important as accurate production. Thus, if a male is encoding complexity and is singing to a female, the female must be able to assess the complexity.
  23. 23. Females Monitor Male Song and Use it in Selecting Mates Bensch & Hasselquist, ‘92
  24. 24. Hearing Song Activates Novel Brain Regions
  25. 25. 7 8 9 NS 0 1 2 3 4 5 6 Social Rearing n = 9 p < 0.05 Deprived Rearing n = 9 Isolate Rearing n = 8 NS Number of Females Female Zebra Finches Learn Song Discrimination Lauay et al., 2004 Social Isolate
  26. 26. Female Finches Reared in Isolation Have Fewer Spine Synapses in NCM Lauay, Komorowski & DeVoogd, 2005 Mean Number of Spines / 12µm of Dendrite * 0 5 10 15 20 25 30 35 40 45 50 Males Females n=5 n=7 n=6 n=5 Control Song Deprived
  27. 27. Summary <ul><li>A dedicated “song system” is used to produce song </li></ul><ul><li>These areas are also responsible for song learning </li></ul><ul><ul><li>Variation in size gives different capacities, </li></ul></ul><ul><ul><li>Opportunity to learn song causes plastic changes in synapses </li></ul></ul>
  28. 28. An Adaptation in Spatial Memory- Food-storing Birds Creates thousands of scattered food caches in Fall Uses memory to retrieve caches during winter
  29. 29. Anatomy of the Avian Hippocampus <ul><li>Location: Surface of the Brain </li></ul><ul><li>Inputs from the Septum and Cortex-like Areas </li></ul><ul><li>BUT… </li></ul><ul><li>No 3-layer organization </li></ul><ul><li>No tri-synaptic pathway </li></ul><ul><li>No DG or other mammal- like components </li></ul>
  30. 30. Hippocampal Lesions Impair Spatial Memory [Sherry & Vaccarino, 1989] Sherry & Vaccarino, ‘89 Caching was unimpaired 0 20 40 60 80 % visits Hp HA Control
  31. 32. Inactivating Hp at Acquisition-- Prevents Spatial Memory Acquisition, No Deficit in Cue-based Memory <ul><li>Infuse with 2% lidocaine prior to memory acquisition </li></ul><ul><li>Assess memory acquisition across 5 trials </li></ul>Shiflett et al (2003) Hippocampus
  32. 33. Inactivating Hp at Retrieval-- Disrupts Recent Memory No Deficit for Remote Memory Shiflett et al (2003) Hippocampus
  33. 34. In mammals, NMDA receptors: 1) Are coincidence detectors 2) Activate second messenger systems within neurons 3) That can change synaptic strength directly 4) Or by activating Immediate Early Genes 5) That then turn on Late Effector and Regulatory Genes 6) To create structural and regulatory proteins 1 2 3 4 5 6
  34. 35. NMDA-R Inactivation Impairs Acquisition, Does not Impair Retrieval Infuse with AP5 prior to memory acquisition or memory retrieval Shiflett et al (2004) Behav. Neurosci
  35. 36. In mammals, the hippocampus has high levels of receptors for steroids from adrenal cortex Chronic stress (which causes the steroids to be released) or steroid administration causes hippocampal shrinkage (for ex., humans--PTSD, rats--chronic restraint)
  36. 37. Captivity Causes the BCC Hp to Shrink 12 birds captured in Dec. Half released, half lab-housed After 5 weeks, wild ones were recaptured. Tel and Hp measured in all. Tarr et al., in press 10 12 14 16 18 20 Hp Volume 225 250 275 300 325 350 Tel Volume Lab Wild
  37. 38. Hippocampus Conclusions <ul><li>The hippocampus is used to encode spatial memory in birds as it is in mammals </li></ul><ul><li>Molecules like NMDA receptors must be activated to form LTM, as in mammals </li></ul><ul><li>The hippocampus pays for its ability to learn rapidly by being sensitive to stress, as in us </li></ul>
  38. 39. 1. Different forms of learning in birds use different brain systems 2. Song learning is slow and enduring, and requires links from motor areas to muscles 3. Spatial learning is rapid but fragile and requires the hippocampus to form it, but not to preserve it Summary
  39. 40. So what? Do birds teach us anything about ourselves?
  40. 41. <ul><li>Motor cortex sends movement signals to spinal cord </li></ul><ul><li>Motor activity is modulated by the basal ganglia </li></ul><ul><li>Motor cortex cells project to basal ganglia, which then project to thalamus, and back to the cortex </li></ul>Motor Cortex
  41. 42. The Motor Song System consists of Production (red) and Regulatory Nuclei (blue)
  42. 43. The Motor Song System consists of Production (red) and Regulatory Nuclei (blue) (Or areas like human pre-motor and motor cortex and basal ganglia) In addition, an area homologous to amygdala is used for emotional learning
  43. 44. Altering Influences on Song System Nuclei in Adults can Alter their Output Normal Canary Kitko & DeVoogd, in prep. lMAN lesion
  44. 45. Different Forms of Learning in Humans use Different Brain Regions Fast, factual, Slow, precise, modifiable[Hp] resists change
  45. 46. Different Forms of Learning in Humans use Different Brain Regions
  46. 47. Different Forms of Learning in Humans use Different Brain Regions
  47. 48. <ul><li>Reading words in a mirror (as in class) </li></ul><ul><li>Patients are just like controls if new sets of words are given (left), but less good than controls if words are used again (right). [Why?] </li></ul>
  48. 49. The Brain of Vertebrates Nieuwenhuys et al., (1998) Last common ancestors were reptile-like
  49. 50. Kumar & Hedges, 1998
  50. 51. : Brain Systems : Learning is divided into similar behavioral classes in birds and mammals. They use brain systems that are alike both in networks and mechanisms to deal with these classes. This must be because these functional distinctions evolved in remote ancestors and have been preserved ever since
  51. 52. Molecular Implications : <ul><li>The molecular basis of synaptic plasticity evolved very early </li></ul><ul><li>and has been highly conserved. </li></ul><ul><li>Understanding how each molecule hands off function to the next is a powerful means of addressing disease. </li></ul>
  52. 53. Functional Implications : If you want to understand normal function: Learn about essential features of the behavior Learn about the brain modifications that give a particular species its abilities Thus, if you want to know how our cognition differs from a mouse, and how various forms of memory are organized across the brain, consider studying unusual systems, even birds!
  53. 54. And Finally Back to my Cousins… <ul><li>Yes, I’m still studying bird brains </li></ul><ul><li>I’ve observed that birds are amazingly bright </li></ul><ul><li>I’ve discovered a bit about how their brains do it </li></ul><ul><li>Because the brains are so different, the birds are helping to show me essential ways about how our brains work </li></ul>
  54. 55. ¡Muchas Gracias!
  55. 56. What about brain systems involved in learning? Humans also use different brain systems for different forms of learning
  56. 57. System Implications: <ul><li>1) Molecular description is unlikely to explain our memory of time or of faces, etc. </li></ul><ul><li>2) Using model systems that seem esoteric could be a powerful means of describing “essences”--the features that are necessary for a particular function. </li></ul><ul><li>Thus, know your question--do you want to describe and possibly fix a malfunction? Study molecules. </li></ul><ul><li>Or do you want to understand normal function-- </li></ul><ul><li>how our cognition differs from a mouse, and how various forms of memory are organized across the brain? [And if the latter, consider unusual systems!] </li></ul>
  57. 58. Molecular : The units (synapses, molecules) for building memory, and the sequence in which they are used are the same.
  58. 59. 7) Species differences in these systems matches behavioral capacity 8) Natural learning can easily be studied in birds 9) Birds are great for comparative and evolutionary questions