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Let’s (Briefly) Break the Brain

Let’s (Briefly) Break the Brain. Introduction to TMS and an Overview of Current Projects. Arman Abrahamyan. … are there TMS studies? Of course. There are a lot. Someone say now is TMS world [unedited]. Skype Chat. [1]. Break It … to Understand. [2]. [3]. Accidental Brain Breakdown.

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Let’s (Briefly) Break the Brain

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  1. Let’s (Briefly) Break the Brain Introduction to TMS and an Overview of Current Projects Arman Abrahamyan

  2. … are there TMS studies? • Of course. There are a lot. Someone say now is TMS world [unedited] Skype Chat

  3. [1] Break It … to Understand

  4. [2] [3] Accidental Brain Breakdown

  5. [4] What is TMS?

  6. Introduction to TMS Current Projects Talk Structure

  7. How does TMS work? • TMS apparatus, major coil types, and modes of stimulation • “Virtual lesion” paradigm • MRI guided coil positioning • Is it safe? Introduction to TMS

  8. How Does TMS Work?

  9. 1831 [5] [6] Electromagnetic Induction

  10. 1896 Reported seeing phosphenes [7], [8] Early Attempts: d’Arsonval

  11. 1910 Replicated d’Arsonval’s results [9], [10] Early Attempts: Thompson

  12. 1911 Electromagnetic field is still not large and rapidly-changing enough Early Attempts: Magnusson & Stevens [11], [12]

  13. Allows starting and • stopping large • electrical currents • within microseconds [13] Thyristor

  14. 1985 First TMS apparatus [14, 31]

  15. EM Induction and TMS [15, 31]

  16. TMS causes depolarisation of neuronal membranes Depolarisation can result in action potential [16] Microscopic Level

  17. Stimulated Area: 1-4 cm3 Affected Neurons: 1-5 billion [17], [18] Macroscopic Level

  18. TMS Apparatus, Coil Types, and Stimulation Modes

  19. [4] TMS Apparatus

  20. Circular Coil [14]

  21. Large Area of Stimulation [19] Secondary Current Induced by Round Coil

  22. Focal Area of Stimulation Induced Electric Field [33, 19] Secondary Current Induced by Double Coil

  23. Stimulation Modes [32, 21]

  24. “Virtual Lesion” Paradigm

  25. Use of TMS

  26. [11, 20, 21] “Virtual Lesion” or Breaking the Brain

  27. No TMS [25] Mechanisms of Interference

  28. TMS No TMS [26] [26] Neural Activity: No TMS vs TMS condition

  29. Noise Injection Signal Suppression [22] [23] Noise Injection or Signal Suppression?

  30. MRI Guided Stereotaxic Navigation of the Coil

  31. [26] Brain is Difficult to See Through the Skull

  32. [27] [28] MRI Guided Neuronavigation [29]

  33. [27] Safety

  34. There are no known side effects associated with single-pulse TMS, when used properly • rTMS is known to cause seizure when stimulation parameters are well beyond accepted safety guidelines [8, 11, 32] Risks of TMS

  35. Currently established safety guidelines for using TMS in rMTS mode are far below the risk margin for inducing a seizure • Participants undergo a screening check [8, 11, 32] Safety of Participants

  36. Participants will be excluded if: • Personal or family history of epilepsy • Brain-related abnormal conditions • Head or brain injuries • Migraines or headaches • Medications for a neurological or psychiatric condition • Implanted devices • Heart condition • Pregnancy [8, 11, 32] Safety of Participants

  37. Conclusions

  38. TMS operates on the principle of electromagnetic induction • TMS is relatively easy to operate and apply • TMS can create a “virtual lesion” in a stimulated area of the brain by interfering with a neural activity in that area • The “virtual lesion” paradigm is useful approach for mapping the temporal and functional characteristics of an area of the brain • Following currently established safety guidelines for TMS, it is possible to significantly reduce, if not eliminate, risks associated with TMS Conclusions

  39. Preliminary results of a pilot experiment • Improving phosphene threshold identification Current Projects

  40. TMS as a Pedestal in Visual Perception

  41. Phosphene threshold • Minimum stimulation level at the occipital pole that induces phosphenes • Suprathreshold TMS • Stimulation level above the phosphene threshold • Subthreshold TMS • Stimulation level below the phosphene threshold Phosphene Threshold

  42. Impairs visual perception Suprathreshold TMS

  43. But what about subthreshold TMS? Subthreshold TMS

  44. Subthreshold magnetic stimulation of the occipital pole will act as a pedestal for a visual stimulus and lower stimulus detection threshold Hypothesis

  45. 2-interval forced-choice task • Task: “Left Shift” button when stimulus is in the first interval, “Right Shift” button when stimulus is in the second interval • Adaptive staircase to identify detection threshold in 30 trials • Stimulus: plaid (2 x ±450 Gabor) • Stimulus duration: 40 ms Method

  46. Single-pulse TMS to occipital pole • 100 ms after stimulus onset • Stimulation intensities: • Varied from 80% - 120% of phosphene threshold • Control: no TMS or stimulation at Cz • Plaid was positioned where phosphene was located Method

  47. Individual data • Average detection threshold by condition EA HP EL EL Preliminary Results

  48. Result seem to support the hypothesis that subthreshold TMS can act as a pedestal • It is contended that the noise injection, as a results of stimulation, acts as a pedestal which improves the stimulus detection threshold • We are devising a final protocol for more systematic testing and data collection • Manipulating levels of subthreshold stimulation • Manipulating the timing of the TMS pulse Conclusions

  49. Justin Harris • Colin Clifford • Ehsan Arabzadeh • Irina Harris • Alexandra Murray • Participants: • Evan Livesey • Hannah Pincham Acknowledgements

  50. [4] Thank you

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