Join us for our continuation Pod of Inquiry episode featuring Dr. Sonny Yamasaki, exploring groundbreaking research on pain transmission and treatment across body symmetry.

Dr. Yamasaki discusses how Single-Limb Pain Treatment can unexpectedly influence pain relief in the corresponding limb on the opposite side. Learn about the neurological mechanisms behind this phenomenon and its implications for chronic pain management.

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Guest Biography

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.

Show Notes from this episode

  • Spinal Thalamic Pathways and Pain Transmission 0:00
    • Dr. Barrett introduces the episode, mentioning it is a continuation of the previous week’s discussion with Dr. Sonny Yamasaki on spinal thalamic pathways and pain transmission.
    • Dr. Yamasaki begins by focusing on cortical areas and brainstem areas involved in pain and pain inhibition, including the periventricular Gray and periaqueductal Gray.
    • The discussion covers the role of the nucleus raphe magnus, which contains enkephalin neurons and releases serotonin, projecting to most parts of the brain and spinal cord.
    • The locus coeruleus, located in the pons, is highlighted for its role in storing norepinephrine and projecting it to the brain and spinal cord to inhibit pain.
  • Role of the Amygdala and Emotional Components 3:03
    • Dr. Yamasaki explains the role of the amygdala in pain inhibition, describing it as a control switch for descending pathways from the cortex.
    • The prefrontal cortex is discussed as a key area involved in consciousness and decision-making, with a role in turning down the volume of pain signals.
    • The amygdala and insula are identified as areas that receive signals from the prefrontal cortex to instruct the brainstem to reduce pain.
    • Dr. Barrett and Dr. Yamasaki discuss the emotional components of pain, with the amygdala and anterior cingulate cortex playing significant roles.
  • Descending Pathways and Pain Inhibition 6:01
    • Dr. Yamasaki describes the role of the periaqueductal gray (PAG) in pain inhibition, noting that it sends signals to lower brainstem nuclei to reduce pain.
    • Early studies in the 1960s and 1970s showed that stimulating the PAG could produce strong pain inhibition, leading to experiments in humans.
    • The discussion covers the challenges and side effects of continuous stimulation, with suggestions for intermittent stimulation to mitigate side effects.
    • Dr. Barrett and Dr. Yamasaki discuss the complexities of norepinephrine as an inhibitory neurotransmitter in the dorsal horn, despite being excitatory in other contexts.
  • Ventral Lateral Medulla and Pain Inhibition 11:22
    • Dr. Yamasaki explains the role of the ventral lateral medulla (VLM) in pain inhibition, noting that a single stimulus can produce long-lasting pain reduction.
    • The VLM sends strong feedback loops to second-order neurons, inhibiting pain signals on both sides of the brain.
    • The dorsal reticular nucleus is mentioned as a facilitatory input that can amplify pain signals, complicating the overall pain inhibition system.
    • Dr. Barrett and Dr. Yamasaki discuss the importance of understanding these complex pathways to treat pain effectively.
  • Diffuse Noxious Inhibitory Control (DNIC) 19:01
    • Dr. Yamasaki introduces the concept of DNIC, where creating pain in one area can inhibit pain in another area, such as slapping the arm to reduce pain in the hand.
    • Historical examples of DNIC include ancient practices like using hot irons or clamping a bull’s nose during castration.
    • The discussion highlights the importance of understanding bilateral systems for both pain and pain inhibition, explaining improvements in untreated limbs.
    • Dr. Barrett and Dr. Yamasaki emphasize the need to treat pain quickly to prevent it from becoming chronic and difficult to treat.
  • Placebo Effect and Clinical Implications 29:21
    • Dr. Yamasaki explains the placebo effect as part of the same circuitry involved in pain inhibition, with the prefrontal cortex playing a key role.
    • The discussion covers how clinicians can use positive reinforcement to enhance the placebo effect, treating it as a valid and important aspect of pain management.
    • Dr. Barrett and Dr. Yamasaki discuss the negative connotations of the term “placebo” and the need to reframe it as a positive clinical tool.
    • The conversation highlights the importance of understanding and leveraging the placebo effect to improve patient outcomes.
  • Summary and Future Directions 39:55
    • Dr. Barrett and Dr. Yamasaki summarize the key points of the discussion, emphasizing the importance of understanding spinal thalamic pathways and pain inhibition.
    • The conversation touches on the need for further research and education to dispel misconceptions about pain treatment and the placebo effect.
    • Dr. Yamasaki mentions plans to write a book on the concept of “set points” in the brain, explaining how the brain regulates various functions like body weight and pain.
    • The discussion concludes with a commitment to continue exploring these complex topics and sharing insights with the medical community.

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