The Characteristics Of Acupoint Pain Perception And Their Cognitive Neural Mechanism

In recent years,acupoints have gradually become the focus of research by researchers at home and abroad because of their unique role in treatment.Many studies on acupoints and pain have been done by predecessors,but most of them focus on the analgesic or sedative effects of acupuncture and acupoint pressure on other parts of the body.However,the characteristics of acupoints themselves and the neural mechanism behind them are still unclear.Previous studies used a single experimental pain induction method rather than a multimodal pain induction method.Pressure pain threshold is a widely used assessment method in the study of pain sensitivity,and electrical stimulation can induce different levels of pain from low to high.Therefore,in this study,pressure stimulation and electrical stimulation were used as pain induction methods.Starting from different pain degrees of individuals,the characteristics of acupoint pain perception and its cognitive neural mechanism were systematically explored from the level of behavioral response and neural response.Study 1 used pressure stimulation to induce pain perception in individuals and explored the pressure pain threshold characteristics of acupoints by analyzing the differences in pressure pain thresholds between acupoints and non-acupoints of the participants.In this study,40 participants were recruited to measure their pressure pain thresholds at a total of 16 locations(half at acuppoints and half at non-acupoints)through a behavioral experiment with a one-factor within-subjects design.The results revealed no significant differences in pressure pain thresholds between participants at both acupoints and non-acupoints,and the pressure pain perception at acupuncture and non-acupuncture points was consistent.Study 2 used electrical stimulation techniques to induce different levels of pain in individuals and explored the nociceptive characteristics of acupoints by analyzing the differences in pain levels between participants at acupoints and non-acupoints.In present study,a one-factor two-level(acupoint,non-acupoint)within-subjects design was used in a behavioral experiment.All 48 participants(24 females)received stimulation separately at acupoints(Zusanli,Neiguan)and non-acupoints(3 cm next to Zusanli and 3 cm next to Neiguan)and correspondingly rated the pain intensity on a9-point Likert Scale.The results revealed that comparing with the non-aucpoints,when participants’ scores were 7～9,there was higher electrical stimulation intensity values,lower pain perception,and less pain sensitivity at acupoints,and thus pain perception at acupoints and non-acupoints was inconsistent.Study 3 explored the nociceptive characteristics of acupoints and their neural processing mechanisms at the level of neural responses by means of event-related potential techniques.A 2(stimulation location: the acupoint,the non-acupoint)× 3(pain intensity: no pain,low pain,high pain)within-subject experimental design was used.In formal experiment,32 participants(16 females)received no pain,low-pain,and high-pain stimuli at acupoints and non-acupoints and performed pain judgment.The nociceptive characteristics of acupoints were explored at the neural response level by observing the changes in the amplitude of individual ERP.The results showed that there was no significant difference in N2 between acupoints and non-acupoints under low-intensity pain stimulation and pain-free stimulation,while under high-pain stimulation,the N2 amplitude of acupoints was significantly lower than that of non-acupoints,indicating that under high-pain stimulation,the EEG amplitude of acupoints was lower than that of non-acupoints and acupoints were more insensitive to pain.Namely,pain perception at acupoints was inconsistent with that of non-acupoints,and for this reason,the results of Study 3 was consistent with study 2.The above findings indicate that low-intensity and painless stimulation do not induce nociceptive differences between acupoints and non-acupoints,whereas in high-pain situations,there was lower pain perception and more insensitivity at the acupoint than at the non-acupoint.Under that circumstance,therefore,pain perception differs between acupoints and non-acupoints,which may support the pain specificity of the acupoint.Present work started with focusing on the pain perception at both the acupoints and the non-acupoints,and futher investigated in depth the nocieceptive differences that exist between the acupoints and non-acupoints at different pain intensity.And the results will help us to understand the nociceptive characteristics of acupoints at different pain intensity,provide new methods to reveal the mechanism of acupoint stimulating,and provide new supporting evidence for the specificity of acupoints.