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Synesthesia

Synesthesia. Romke Rouw University of Amsterdam. Synesthesia. automatic (fast and seemingly effortless) consistent since early youth subjective (individual) highly specific familial trait. Grapheme – Color Synesthesia. “The letter A is pale blue” “100 is black and white”

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Synesthesia

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  1. Synesthesia Romke Rouw University of Amsterdam

  2. Synesthesia • automatic (fast and seemingly effortless) • consistent • since early youth • subjective (individual) • highly specific • familial trait

  3. Grapheme – Color Synesthesia “The letter A is pale blue” “100 is black and white” “w is light-brownish-yellow”

  4. Perceptual reality

  5. visual search Palmeri et al. 2002

  6. visual search Palmeri et al. 2002

  7. Subtypes Grapheme – Color Synesthesia  A

  8. Subtypes Grapheme – Color Synesthesia projector versus associator  A

  9. Explanation?

  10. Cross – activation • grapheme and color areas adjacently located in the fusiform gyrus Hubbard et al.

  11. Disinhibited feedback • Feedback can also flow back from a multisensory nexus such as the superior temporal sulcus, posterior parietal lobe, intraparietal cortex, or temporo-parietal-occipital junction

  12. Re-entrant processing • Feedback from processing graphemic meaning in anterior fusiform travels back to posterior inferior temporal regions and V4/V8

  13. Synesthesia & DTI with Steven Scholte

  14. Subjects • 18 females • Age range 18 – 43 (mean age 28.7) • 90 % consistency • No history of psych. disease • 18 matched controls 

  15. Synesthetic colors? • Colors of digits/letters/days of the week, retest after three weeks • Eight digit/letters that give a strong, weak, or no synesthetic color experience

  16. How to measure... • Behavioral, fMRI and DTI measurements

  17. Synesthesia & DTI Two questions 1. Are there structural differences between synesthetes and non-synesthetes ? 2. Different neurological mechanisms for projectors and associators?

  18. Synesthesia & DTI Question 1 Are there structural differences between synesthetes and non-synesthetes?

  19. DTI • FA: Diffusion Anisotropy Indice • Degree to which the three tensor eigenvalues differ from one another

  20. DTI • FA: Diffusion Anisotropy Indice • Degree to which the three tensor eigenvalues differ from one another • White matter properties

  21. Synesthetes > non-synesthetes • bilateral cluster in frontal cortex • left superior parietal cortex • right inferior temporal cortex Increased structural connectivity in synesthesia

  22. Synesthetes > non-synesthetes

  23. Tractography results

  24. Synesthetes > non-synesthetes

  25. Tractography results

  26. DTI & fMRI

  27. Synesthesia & DTI Question 2 Projectors versus Associators?   A A

  28. How can this be measured... • Geef aan in hoeverre deze stellingen overeenkomen met uw synesthetische ervaringen (1 =sterk mee oneens, 5 = sterk mee eens), mits anders aangegeven. • 1 Wanneer ik naar een bepaalde letter of cijfer kijk, dan zie ik een specifieke kleur • 1 2 3 4 5 • 2 Wanneer ik naar een bepaalde letter/cijfer kijk, verschijnt de bijbehorende kleur alleen in mijn gedachten en niet ergens buiten mijn hoofd (zoals op het papier) • 1 2 3 4 5 • ...

  29. Questionnaire • “projector” vs “associator” questions: • when I look at a certain letter or digit, I really see a particular color • I see the color of the letter/digit only in my head • five-point Likert Scale questions

  30. Projector versus Associator? PA score projector associator

  31. Projector versus Associator? Max. range is from -4 to 4 Mean = 0.08 St.Dev = 2.261 N = 18

  32.  A A

  33. FA values subtypes of synesthesia rs(17) = .548, p = .019 rs(17) = -.098, p = .699

  34. Current study…

  35. FA values subtypes of synesthesia rs(6) = .679 rs(10) = - .018

  36. Synesthesia & DTI Two questions 1. Structural differences between synesthetes and non-synesthetes ? 2. Neurological mechanisms different for projectors and associators?

  37. Conclusions (1) • Increased connectivity in synesthetes: • Frontal, parietal, inferior temporal cortex • Increased connectivity and correlation between FA and BOLD provides support for cross-activation theory • However, both fMRI and DTI show a role of higher brain areas in synesthesia.

  38. Conclusions (2) • Of particular interest is a cluster of increased connectivity in inferior temporal cortex, near fusiform gyrus • The strength of connectivity in this area correlates with the nature of synesthetic experience • Rouw, R. & H.S. Scholte (2007). Nature Neuroscience,(10),792-797.

  39. Thank you

  40. Increased FA in sup frontal cortex

  41. Increased FA in left parietal cortex

  42. Hubbard et al.

  43. Synesthetes > non-synesthetes

  44. grapheme task italic normal

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