Neural Mechanism Of Pain Sensitivity

Pain is a very common and complex subjective experience,which is associated with actual or potential tissue damage.It is a multidimensional phenomenon including perception components and emotional components.Pain is a common physiological phenomenon,but it is also a subjective experience.As a result,pain experience is affected by a variety of factors.Most often,individuals’ feelings to the same stimulate of pain always are different.Therefore,pain is a highly personalized experience.Pain sensitivity reflects ones’ ability to perceive pain.People with high pain sensitivity always feel more painful to the same pain stimulate than low sensitive people.Pain sensitivity reflects personal differences of pain feeling,which has been widely concerned.Pain conductive pathway theory holds that neural pathways of pain can be divided into medial and lateral route,and they responsible for the transmission and encoding the emotional and perceptive components of pain.Each route is an independent system to process the different aspect pain information.However,it is unclear that individual differences in pain sensitivity are due to the differences in process of pain perceptive components or emotional components.In this study,we investigated the neural mechanism of individual differences in pain sensitivity by behavioral research and neural imaging studies.First,we detect personal differences in pain perception in behavioral study.We measured the perceptive characteristics of 70 healthy college students on laser stimulation.We collected laser pain threshold and the subjective evaluation of different stimulate strength in pain intensity and novelty.We use laser pain threshold as a criterion to divide all subjects into the high and low pain groups and then analysis their subjective evaluation of intensity and novelty to the same energy(3J)laser stimulations.The behavioral study results showed that the two pain sensitivity groups have significantly different subjective evaluation of intensity and novelty both in the left or right side.High pain sensitivity group rated significantly higher scores than the low sensitivity group,but not significant difference in gender.Then,we use the Neuro Synth method to analyze the existing pain related neural imaging studies to find the brain regions that closely related to pain processing.The meta analysis results showed that the brain regions related to pain processing including right precentral gyrus,left postcentral gyrus,left middle frontal gyrus,medial frontal gyrus,right cingulate gyrus,left anterior cingulate,left insula,left occipital gyrus,right cerebellum anterior lobule and left cerebellum posterior lobule.According to previous research,primary sensory cortex and thalamus are the key regions for perception process,the anterior cingulate cortex and insula closely related to emotion process.So,we use the parts of these regions overlapped with meta-analysis results as the region of interest(ROI)for our next study to detect the mechanism of pain sensitivity.In study 3,we analysis the gray matter volume and spontaneous brain activity in ROIs using the methods of GMV and Re Ho、ALFF.The results indicated that lateral and medial pain system play different role in pain sensitive.Analysis of gray matter volume found significant group differences in left and right side primary sensory cortex.Resting state MRI showed that the Re Ho value of high sensitivity group is greater than the low sensitivity group in the right side primary somatosensory cortex,and low sensitivity group had a significant high ALFF value in right insula.Combine the two f MRI results,the capacity of primary somatosensory cortex is different between two groups.S1 of high sensitive group has a better capability,which may be the real reason for their sensitive to pain stimulations.So,the difference in subjective evaluation of pain between the high and low pain sensitivity groups may be due to the individual’s bias in perceptive information process.In present study,we detected the characteristics of pain perception using behavioral method,meta-analysis and functional magnetic resonance.The behavioral results indicated that there is a significantly individual difference between the two groups in intensity and novelty.The result of meta-analysis is in line with the existing researches,which are in the range of ‘pain matrix’.MRI studies on ROIs found the group differences of gray matter volume and spontaneous brain activity in S1,which is a key region of medial pain system.The results of our studies indicated that the individual differences of pain sensitivity may be due to the differences in the processing of perceptive information.The results of this study have important implications for our understanding of the neural mechanisms of pain sensitivity,which also has clinical sense.