An FMRI Investigation Of The Resting-State Brain Activity In Idiopathic Trigeminal Neuralgia

Idiopathic trigeminal neuralgia(ITN) is characterized by paroxysmal, electric, lancinating pains and a variety of sensory experiences with unknown origin. Prevailing pathophysiology of ITN emphasizes its peripheral nociception and central component mechanisms. Peripheral nociception describes the hyperexcitability of the nerve-vessel conflict, whereas the central component relates to central facilitation and results in central hyperexcitability of the trigeminal system that is initiated or sustained by peripheral mechanisms. A major goal of recent efforts to map the organizational principles of human brain has been facilitated by the use of resting-state f MRI, among which methods measure local activity(Amplitude of Low-frequency Fluctuation, ALFF),short-distance functional interactions like regional homogeneity(Re Ho) and interhemispheric functional connectivity(voxel-mirrored homotopic connectivity, VMHC) have been widely used to reveal pathophysiological profiles in brain disorders. Detection of intrinsic brain activity is more suitable for disorders under pain background, promoting new biological significance and potential pathophysiological information for ITN. In this study, we used the aforementioned methods(i.e., ALFF, Re Ho, VMHC) of resting-state f MRI to explore spontaneous brain activity changes and its correlation with clinical pain scales in ITN patients, allow for a better understanding of the underlying pathophysiological mechanisms.Part Ⅰ Regional homogeneity of spontaneous brain activity in ITNObjective: To investigate local synchronization of spontaneous brain activity in patients with ITN and its correlation with clinical variables of pain.Methods: Resting-state f MRI(rsf MRI) data from seventeen patients with ITN and nineteen age- and sex-matched healthy controls were analyzed using regional homogeneity(Re Ho) analysis, which is a data-driven approach used to measure the regional synchronization of spontaneous brain activity.Results: Patients with ITN had decreased Re Ho in the left amygdala, right parahippocampal gyrus and left cerebellum and increased Re Ho in the right inferior temporal gyrus, right thalamus, right inferior parietal lobule, and the left postcentral gyrus(corrected). Furthermore, the increase of Re Ho in the left precentral gyrus was positively correlated with visual analogue scale(r = 0.54; p = 0.002).Conclusion: In summary, our results provide novel evidence for the altered local synchronization of low-frequency spontaneous activity across central pain processing brain regions in patients with ITN. Furthermore, a positive relationship between pain intensity and Re Ho in the sensorimotor areas was identified. This may reflect the maladaptive process of daily pain attacks, while other Re Ho changes across distributed brain regions may indicate a central role for the pathophysiology of ITN. Broadly, our findings have implications for understanding how ITN affects local intrinsic brain activity.Part Ⅱ Amplitude of low-frequency fluctuations ofrs-f MRI in ITNObjective: Using amplitude of low-frequency fluctuation(ALFF) measured by resting state f MRI, we examined the ALFF changes to localize abnormal spontaneous brain activity, and correlated brain activity changes in resting state with behavior estimates.Methods: Resting-state f MRI(rsf MRI) data obtained from seventeen patients with ITN(7 male / 10 female, age = 63.41 ± 7.25 years) and nineteen age- and sex-matched healthy controls(9 male/10 female, age = 61.75 ± 6.02 years) were analyzed using ALFF method.Results: Patients with ITN showed increases of ALFF in bilateral temporal gyri, and decreased ALFF in the core(medial prefrontal, cingulate and precuneus cortices) of default mode network as well as right caudate(p < 0.05, Alpha Sim correction).Conclusion: Patients with ITN are associated with decreased spontaneous brain activity across the default and basal ganglia systems, and increased intrinsic activity in regions involved in multidimensional sensory processing, these abnormalities may underline the pathophysiological basis of ITN that continually process nociceptive inputs, and aberrant large scale intrinsic network organization.Part Ⅲ Interhemispheric coordination in ITNObjective: Previous morphometric and structural findings indicate the interhemisphereic impairments of ITN. Efficient interhemisphereic functional communications are crucial to multiscale sensory interactions, cognitive processing and different levels of complex during the development. In this section, we utilized voxel-mirrored homotopic connectivity(VMHC) of resting f MRI to investigate the interhemisphereic interactions of ITN, and aimed to relate VMHC changes with underlying pathophysiological mechanisms of ITN.Methods: We performed VMHC analyses on resting state f MRI data from seventeen patients with ITN(7 male / 10 female, age = 63.41 ± 7.25 years) and nineteen age- and sex-matched healthy controls(9 male/10 female, age = 61.75 ± 6.02 years).Results: We found significant reductions in VMHC in patients in bilateral parahippocampal gyri and orbitofrontal cortices(p < 0.05, Alpha Sim correction). No regions of increased VMHC were detected in patients.Conclusion: Patients with ITN showed reduced inter-hemispherical interactions between the orbitofrontal cortices and parahippocampal gyri, these decreases may reflect compromise on cognitive-emotion regulation and decision-making processing. This findings support previous reports, also suggests a new way to better understanding the pathophysiology of ITN.