Headache & Orofacial Pain Effort Lab, Biologic and Materials Sciences & Prosthodontics Department, University of Michigan School of Dentistry, Ann Arbor, MI, United States.
Department of Orthodontics and Pediatric Dentistry, University of Michigan School of Dentistry, Ann Arbor, MI, United States.
J Med Internet Res. 2021 Oct 12;23(10):e27298. doi: 10.2196/27298.
Pain is a complex experience that involves sensory-discriminative and cognitive-emotional neuronal processes. It has long been known across cultures that pain can be relieved by mindful breathing (MB). There is a common assumption that MB exerts its analgesic effect through interoception. Interoception refers to consciously refocusing the mind's attention to the physical sensation of internal organ function.
In this study, we dissect the cortical analgesic processes by imaging the brains of healthy subjects exposed to traditional MB (TMB) and compare them with another group for which we augmented MB to an outside sensory experience via virtual reality breathing (VRB).
The VRB protocol involved in-house-developed virtual reality 3D lungs that synchronized with the participants' breathing cycles in real time, providing them with an immersive visual-auditory exteroception of their breathing.
We found that both breathing interventions led to a significant increase in pain thresholds after week-long practices, as measured by a thermal quantitative sensory test. However, the underlying analgesic brain mechanisms were opposite, as revealed by functional near-infrared spectroscopy data. In the TMB practice, the anterior prefrontal cortex uniquely modulated the premotor cortex. This increased its functional connection with the primary somatosensory cortex (S1), thereby facilitating the S1-based sensory-interoceptive processing of breathing but inhibiting its other role in sensory-discriminative pain processing. In contrast, virtual reality induced an immersive 3D exteroception with augmented visual-auditory cortical activations, which diminished the functional connection with the S1 and consequently weakened the pain processing function of the S1.
In summary, our study suggested two analgesic neuromechanisms of VRB and TMB practices-exteroception and interoception-that distinctively modulated the S1 processing of the ascending noxious inputs. This is in line with the concept of dualism (Yin and Yang).
疼痛是一种复杂的体验，涉及感觉辨别和认知情感神经元过程。跨文化研究早就发现，正念呼吸（MB）可以缓解疼痛。人们普遍认为，MB 通过内感受来发挥其镇痛作用。内感受是指有意识地将注意力重新集中到内部器官功能的身体感觉上。
在这项研究中，我们通过对接受传统 MB（TMB）的健康受试者的大脑进行成像，来剖析大脑的镇痛过程，并将其与另一组通过虚拟现实呼吸（VRB）将 MB 增强为外部感觉体验的受试者进行比较。
VRB 方案涉及内部开发的虚拟现实 3D 肺，它与参与者的呼吸周期实时同步，为他们提供呼吸的沉浸式视觉听觉外感受。
我们发现，经过为期一周的练习，两种呼吸干预都导致了疼痛阈值的显著增加，这是通过热定量感觉测试来衡量的。然而，功能近红外光谱数据显示，潜在的镇痛大脑机制是相反的。在 TMB 练习中，前额叶皮层前部独特地调节了运动前皮层。这增加了它与初级体感皮层（S1）的功能连接，从而促进了基于 S1 的呼吸感觉-内感受处理，但抑制了其在感觉辨别疼痛处理中的其他作用。相比之下，虚拟现实诱导了增强的视觉听觉皮质激活的沉浸式 3D 外感受，这减弱了与 S1 的功能连接，从而削弱了 S1 的疼痛处理功能。
总之，我们的研究提出了 VRB 和 TMB 练习的两种镇痛神经机制——外感受和内感受——它们分别调节了上行伤害性传入的 S1 处理。这与二元论（阴阳）的概念一致。
