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Dr. Sonny Yamasaki

Dr. Yamasaki is the President and Co-founder of Enso Medical Technologies, Inc.  He is a graduate of the Rutgers Medical School (now Robert Wood Johnson Med. Sch.) and UMDNJ- Graduate School of Biomedical Sciences.

He is a neurophysiologist who studied recovery mechanisms of injured cerebral cortex in the visual and oculomotor systems of awake, behaving, non-human primates.

He conducted this research as a Postdoctoral Fellow, and later Scientific Staff Fellow at the National Eye Institute, NIH; and as Assistant Professor at the Univ. of Wisconsin Medical School, Madison. In his corporate career he was a Technical Fellow and lead stroke expert for Medtronic PLC for 17 years.

• Introduction and Overview of the Podcast 0:00
  • Barrett welcomes listeners and introduces his guest, Dr. Sonny Yamasaki, highlighting his expertise in neuroscience and pain pathways.
  • Barrett mentions Dr. Yamasaki’s lecture at the Association of Extremity Nerve Surgeons meeting in November 2024 and expresses excitement about revisiting the topic.
  • Barrett shares a personal anecdote about a patient experiencing pain relief in an untreated extremity after surgery on another extremity, hinting at the complexities of pain management.
• Yamasaki’s Lecture and Initial Findings 4:54
  • Barrett explains the mystery of pain relief in untreated extremities and credits a lecture by Ian Carroll for providing insights into neurophysiological phenomena.
  • Yamasaki begins his lecture, explaining the initial disconcerting findings of the Shai Rozen study showing equal improvement in both treated and untreated legs.
  • Yamasaki introduces the concept of bilateral pain pathways, including the Paleo and Arche spinal filament tracts, which can explain the improvement in both legs.
  • He emphasizes the descending inhibitory pain pathway that starts in the cerebral cortex and extends to the spinal cord, contributing to the bilateral pain relief observed in the study.
• Explanation of Dr. Rozen’s Study 7:18
  • Yamasaki summarizes Dr. Rozen’s level one study, the diabetic neuropathy nerve decompression trial (DNND trial), highlighting its rigorous design and findings.
  • He explains that both treated and sham surgery legs improved equally at 12 months, but the treated legs continued to improve significantly at 56 months.
  • Yamasaki presents a graph showing the gradual improvement in treated legs and the plateau in sham-treated legs, suggesting a placebo effect.
  • He sets the stage for explaining the findings using the concept of bilateral pain pathways and the descending inhibitory pain pathway.
• Understanding Spinothalamic Tracts 10:35
  • Yamasaki introduces the three spinothalamic tracts: Neo, Paleo, and Arche, explaining their roles in pain and temperature perception.
  • He describes the Neo spinothalamic tract as the most recent and fastest, responsible for fast, localizable pain.
  • The Paleo and Arche spinothalamic tracts are older and slower, responsible for slower, more emotional and non-discriminative pain.
  • Yamasaki shares a personal anecdote to illustrate the difference between fast and slow pain, emphasizing the emotional and non-localizable nature of slow pain.
• Visual Aids and Detailed Explanation 18:44
  • Yamasaki uses visual aids to explain the spinothalamic tracts, showing their locations and functions in the spinal cord and brain.
  • He describes the circuitry of pain signals, including the dorsal horn, anterior white commissure, and the spinothalamic tracts.
  • Yamasaki explains the bilateral nature of the Paleo and Arche spinothalamic tracts, which can explain the improvement in both treated and untreated legs.
  • He highlights the importance of understanding these pathways to better manage pain and improve patient outcomes.
• Descending Inhibitory Pathways 29:36
  • Yamasaki introduces the concept of descending inhibitory pathways, which help diminish pain signals.
  • He explains that the prefrontal cortex sends signals to the brainstem, which then inhibit pain signals at the spinal cord level.
  • Yamasaki emphasizes the importance of treating pain quickly to prevent progression to more severe conditions like complex regional pain syndrome.
  • He discusses the role of the amygdala, insula, and other brain regions in pain perception and management.
• Gate Control Theory of Pain 36:32
  • Yamasaki explains the gate control theory of pain, proposed by Melzack and Wall, which suggests that large diameter axons can inhibit pain signals.
  • He describes the role of inhibitory interneurons in the substantia gelatinosa, which can be activated to diminish pain signals.
  • Yamasaki uses the example of rubbing an injured knee to illustrate how activating large fibers can inhibit pain signals.
  • He emphasizes the importance of understanding this mechanism to manage pain effectively.
• Clinical Evidence and Functional MRI 36:51
  • Yamasaki presents clinical evidence showing bilateral pain pathways, using functional MRI to demonstrate different brain regions activated during pain.
  • He explains that different parts of the brain, including the cingulate gyrus, dorsolateral prefrontal cortex, and insula, light up during pain perception.
  • Yamasaki discusses the role of the prefrontal cortex in inhibiting pain signals and the importance of understanding these pathways for effective pain management.
  • He highlights the need for further research to fully understand the complexities of pain perception and management.
• Conclusion and Final Thoughts 46:39
  • Barrett summarizes the key points of the lecture, emphasizing the importance of understanding multiple pain pathways and the descending inhibitory pathway.
  • He discusses the potential for genetic factors to influence pain perception and the importance of treating pain quickly to prevent chronic conditions.
  • Yamasaki and Dr. Barrett discuss the complexities of pain management and the need for continued research and education in the field.
  • The podcast concludes with a reminder of the importance of understanding neurophysiological pathways to improve patient care and outcomes.

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