Reduced corticostriatal functional connectivity in temporomandibular disorders

A minireview of the anatomical and pathological factors pertaining to Costen's syndrome symptoms

Objective: Interest in the symptoms pertaining to Costen's syndrome has revived in recent years. The aim of this work is to address the symptoms of Costen's syndrome from the basic science perspectiveMethods: A minireview of the literature related to Costen's syndrome symptoms was performed by retrieving relevant articles from the PubMed database from 1980 until 2021.Results: The validity of Costen's syndrome symptoms has been confirmed by a multitude of articles. Conclusion: Maladaptive plasticity in the central nervous system pathways probably accounts for the incidence and severity of Costen's syndrome symptoms.

Neuroscience contributes to the understanding of the neurobiology of temporomandibular disorders associated with stress and anxiety

OBJECTIVE

This review proposes a neurobiological model for temporomandibular disorders (TMD) associated with stress and anxiety.

METHODS

An electronic search was performed in the PubMed, Embase, and Web of Science databases. Articles published up to 2020 were selected. The search terms were the following: temporomandibular disorders, anxiety, stress, neurobiology of stress and anxiety, and orofacial pain.

RESULTS

In total, there were 100 studies, which presented a total of 10 different analyses. The results were described, demonstrating the type of analysis that was performed on each item analyzed for a better understanding of the context.

CONCLUSION

The conclusion is that the interactions between the masticatory system, temporomandibular joints (TMJs), and stomatognathic apparatus with "stress neuromatrix," "pain neuromatrix," "limbic system," and "neuroimmunoendocrine system" would produce the range of changes observed in neural connectivity and the diversity of symptoms presented in TMD.

Brain alterations in sensorimotor and emotional regions associated with temporomandibular disorders

OBJECTIVES

Temporomandibular disorders (TMD) are characterized by sensorimotor and psychological dysfunction, with evidence revealing the implication of a dysfunctional central nervous system. Previous magnetic resonance imaging (MRI) studies have reported brain alterations in TMD, but most studies focused on either structure or function by a single modality of MRI and investigated static functional connectivity (FC) in TMD. By combining structural and functional MRI data, the present study aimed to identify brain regions with structural abnormalities in TMD patients and examine static and dynamic FC seeded by these regions to investigate structural brain alterations and related disrupted FC underlying the pathophysiology of TMD.

METHODS

We recruited 30 TMD patients and 20 healthy controls who underwent 3.0 T MRI scanning with T1-weighted images using a three-dimensional magnetization-prepared rapid gradient-echo sequence and resting state functional images using a gradient-echo echo-planar imaging sequence. Cortical thickness, volume, surface area, and subcortical volume were calculated, where brain areas with significant structural between-group differences were treated as seeds for static and dynamic FC analyses.

RESULTS

In this preliminary study, we found between-group alterations in sensorimotor regions including decreased cortical thickness in the right sensorimotor cortex as well as decreased volume in the left putamen and associated reduced dynamic FC with the anterior midcingulate cortex; and alterations in emotion processing and regulation regions including decreased volume/surface area in the left posterior superior temporal gyrus and associated increased dynamic FC with the precuneus in TMD patients than controls, having all p < 0.05 with corrections for multiple comparisons.

CONCLUSION

Our findings of structural and functional abnormalities in brain regions implicated in sensorimotor and emotional functions provided evidence for the biopsychosocial model of TMD and facilitated our understanding of the pathophysiological mechanism underlying TMD. The associations between neuroimaging results and clinical measurements of TMD warrant further exploration.

Otological symptoms in patients with rheumatoid arthritis of the temporomandibular joint

OBJECTIVE

The aim of the current study was to describe the pattern of otological symptoms in patients with rheumatoid arthritis (RA), having clinical temporomandibular joint (TMJ) involvement. This issue had not been previously addressed.

METHODS

A questionnaire and examination findings protocol was applied for 141 patients with RA and 141 control subjects.

RESULTS

Otological symptoms (otalgia, hearing loss, tinnitus, and vertigo), all had a significantly higher incidence in RA patients, compared to control subjects (P = .001).

CONCLUSION

The onset and maintenance of otological symptoms in patients with TMJ involvement by RA probably result from peripheral, as well as central nervous system alterations in sensory stimuli programming.

Altered brain responses to noxious dentoalveolar stimuli in high-impact temporomandibular disorder pain patients

High-impact temporomandibular disorder (TMD) pain may involve brain mechanisms related to maladaptive central pain modulation. We investigated brain responses to stimulation of trigeminal sites not typically associated with TMD pain by applying noxious dentoalveolar pressure to high- and low-impact TMD pain cases and pain-free controls during functional magnetic resonance imaging (fMRI). Fifty female participants were recruited and assigned to one of three groups based on the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) and Graded Chronic Pain Scale: controls (n = 17), low-impact (n = 17) and high-impact TMD (n = 16). Multimodal whole-brain MRI was acquired following the Human Connectome Project Lifespan protocol, including stimulus-evoked fMRI scans during which painful dentoalveolar pressure was applied to the buccal gingiva of participants. Group analyses were performed using non-parametric permutation tests for parcellated cortical and subcortical neuroimaging data. There were no significant between-group differences for brain activations/deactivations evoked by the noxious dentoalveolar pressure. For individual group mean activations/deactivations, a gradient in the number of parcels surviving thresholding was found according to the TMD pain grade, with the highest number seen in the high-impact group. Among the brain regions activated in chronic TMD pain groups were those previously implicated in sensory-discriminative and motivational-affective pain processing. These results suggest that dentoalveolar pressure pain evokes abnormal brain responses to sensory processing of noxious stimuli in high-impact TMD pain participants, which supports the presence of maladaptive brain plasticity in chronic TMD pain.

The functional connectivity of the basal ganglia subregions changed in mid-aged and young males with chronic prostatitis/chronic pelvic pain syndrome

Background

The Basal ganglia (BG) played a crucial role in the brain-level mechanisms of chronic pain disorders. However, the functional changes of BG in chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) are still poorly understood. This study investigated the BG subregions’ resting-state functional connectivity (rs-FC) in CP/CPPS patients compared with healthy controls.

Methods

Twenty eight patients with CP/CPPS and 28 age- and education-matched healthy males underwent clinical measurements and 3T brain MR imaging, including T1-weighted structural images and resting-state functional imaging. The data were analyzed by the seeded-based rs-FC analysis. Then, a machine learning method was applied to assess the feasibility of detecting CP/CPPS patients through the changed rs-FC.

Results

Compared with healthy males, patients presented decreased rs-FC between the BG subregions and right middle cingulate cortex, and correlated with pain (r = 0.51, p-uncorrected = 0.005) and urinary symptoms (r = –0.4, p-uncorrected = 0.034). The left superior temporal gyrus and right supramarginal gyrus showed decreased rs-FC with the BG subregions as well. The area under the receiver operating characteristic curve of 0.943 (accuracy = 80%, F1-score = 80.6%) was achieved for the classification of CP/CPPS patients and healthy males with support vector machine (SVM) based on the changed rs-FC.

Conclusion

These findings provide evidence of altered BG subregions’ rs-FC in CP/CPPS, which may contribute to our understanding of the BG’s role in CP/CPPS.

Disrupted Spontaneous Neural Activity and Its Interaction With Pain and Emotion in Temporomandibular Disorders

Background and Purpose

Temporomandibular disorders (TMD), especially pain-related TMD, are closely related to social and psychological factors. We aimed to measure changes in spontaneous brain activity and its related functional connectivity (FC), as well as FC characteristics within the mood-regulating circuits (MRC) in TMD patients by resting-state functional magnetic resonance imaging (RS-fMRI), and to analyze the relationship between these parameters and emotional symptoms.

Materials and Methods

Twenty-one adult TMD patients and thirty demographically matched healthy controls (HCs) underwent clinical scale evaluation and RS-fMRI scanning. After processing RS-fMRI data, the values of the amplitude of low-frequency fluctuation (ALFF) between the two groups were compared. Regions with abnormal ALFF values were selected as areas of interest (ROIs) to compare the differences of whole-brain seed-based FC between groups. The FCs between regions within MRC were also analyzed and compared. In addition, the relationships between RS-fMRI characteristics and pain and mood were explored by correlation and mediation analyses.

Results

Compared with HCs, TMD patients showed increased ALFF in the right parahippocampal gyrus (PHG), the right supplementary motor area, and the bilateral precentral gyrus, with decreased ALFF in the right cerebelum_crus2. Patients showed enhanced right PHG-related FC in the vermis and posterior cingulate cortex, orbitofrontal cortex (OFC)-related FC in the striatal-frontal regions, while decreased dorsolateral prefrontal cortex-related FC in the amygdala. In TMD patients, ALFF values in the right PHG and FC values between the right PHG and the vermis were positively correlated with depressive symptoms. Abnormal FCs in the left striatal-orbitofrontal pathway were correlated with pain and depressive symptoms. More importantly, mediation analysis revealed that chronic pain mediates the relationship between FC of right PHG with vermis and depressive symptoms, and abnormal FC in the left striatal-orbitofrontal pathway can mediate the association between pain and depressive symptoms.

Conclusion

TMD patients have dysregulated spontaneous activity and FC in the default mode network, sensorimotor network and pain-related regions, as well as dysfunction of the fronto-striatal-limbic circuits. The development of negative emotions in TMD may be related to the dysfunction of components within the reward system (especially hippocampus complex, OFC, striatum) due to chronic pain.

A clinical study on the incidence of internal derangement of the temporomandibular joint following harvesting of temporalis fascia

OBJECTIVE

The aim of the current clinical study was to reveal whether harvesting of a temporalis fascia graft would be associated with a higher incidence of temporomandibular joint (TMJ) internal derangement.

METHODS

The study group involved 104 patients who had middle-ear operations, 67 of which involved harvesting of temporalis fascia and 37 that did not. The TMJs were clinically examined in each group.

RESULTS

The total incidence of internal derangement of the TMJ was significantly higher in the group that had temporalis fascia harvesting (79.1%), compared to the group that did not have temporalis fascia harvesting (29.7%), (p= 0.001).

CONCLUSION

Harvesting of temporalis fascia probably alters mandibular kinematics and predisposes to internal derangement of the TMJs.

Abnormal static and dynamic brain function in patients with temporomandibular disorders: a resting-state functional magnetic resonance imaging study

OBJECTIVES

This study was conducted to investigate the brain function of patients with temporomandibular disorders (TMD) by combining the static and dynamic amplitudes of low-frequency fluctuation (ALFF).

METHODS

Thirty patients with TMD and 20 healthy controls were enrolled. All the participants completed their questionnaires, received clinical examinations, and underwent resting-state functional magnetic resonance imaging scanning. We compared the static and dynamic ALFF between the patients and healthy controls by conducting a two-sample t-test with AlphaSim correction for multiple comparisons. The correlation between the static and dynamic ALFF of the brain regions with significant group differences and clinical measurements was analyzed.

RESULTS

The patients with TMD showed increased static and dynamic ALFF in the posterior cingulate cortex compared with that of the controls (whole-brain level, uncorrected P=0.005; region of interest level with AlphaSim correction, voxel level P<0.005, cluster level P<0.05). The dynamic ALFF of the posterior cingulate cortex was negatively correlated with bilateral condylar vertical discrepancies. The dynamic ALFF in the medial orbitofrontal cortex of the patients with TMD was greater than that of the controls (whole-brain level AlphaSim correction, voxel level P<0.005, cluster level P<0.05).

CONCLUSIONS

Our findings revealed that the resting-state brain function of the posterior cingulate cortex and the medial orbitofrontal cortex of patient with TMD increased. These changes probably indicated the potential central mechanisms underlying the increased self-relevant thoughts, negative emotion, and abnormal emotion regulation in TMD.

The Medial Thalamus Plays an Important Role in the Cognitive and Emotional Modulation of Orofacial Pain: A Functional Magnetic Resonance Imaging-Based Study

The thalamus plays a critical role in the perception of orofacial pain. We investigated the neural mechanisms of orofacial pain by exploring the intrinsic functional alterations of the thalamus and assessing the changes in functional connectivity (FC) between the thalamic subregions with significant functional alterations and other brain regions in orofacial pain using the seed-based FC approach. There were 49 participants in the orofacial pain group and 49 controls. Orofacial pain was caused by orthodontic separators. The resting-state functional magnetic resonance imaging data of the two groups were analyzed to obtain the fractional amplitude of low-frequency fluctuations (fALFF) of the thalamus; the thalamic subregions with significant fALFF abnormalities were used as seeds for FC analysis. Student's t-tests were used for comparisons. Pearson's correlation analysis was performed using SPM software. Forty-four participants with orofacial pain (mean age, 21.0 ± 0.9 years; 24 women) and 49 age- and sex-matched controls (mean age, 21.0 ± 2.6 years; 27 women) were finally included. Compared with the control group, the orofacial pain group demonstrated the following: (1) increased function in the dorsal area of the thalamus and decreased function in the medial thalamus; (2) decreased FC between the medial thalamus and 12 brain regions (p < 0.05, family-wise error corrected, voxel > 100); and (3) potential positive and negative correlations between the medial thalamus-seeded FC and visual analog scale score changes (p < 0.05, AlphaSim corrected). The findings show that the medial and dorsal thalami play important roles in orofacial pain perception, and that the medial thalamus likely plays an important role in the cognitive and emotional modulation of orofacial pain.

The neuro-pathophysiology of temporomandibular disorders-related pain: a systematic review of structural and functional MRI studies

Chronic pain surrounding the temporomandibular joints and masticatory muscles is often the primary chief complaint of patients with temporomandibular disorders (TMD) seeking treatment. Yet, the neuro-pathophysiological basis underlying it remains to be clarified. Neuroimaging techniques have provided a deeper understanding of what happens to brain structure and function in TMD patients with chronic pain. Therefore, we performed a systematic review of magnetic resonance imaging (MRI) studies investigating structural and functional brain alterations in TMD patients to further unravel the neurobiological underpinnings of TMD-related pain. Online databases (PubMed, EMBASE, and Web of Science) were searched up to August 3, 2019, as complemented by a hand search in reference lists. A total of 622 papers were initially identified after duplicates removed and 25 studies met inclusion criteria for this review. Notably, the variations of MRI techniques used and study design among included studies preclude a meta-analysis and we discussed the findings qualitatively according to the specific neural system or network the brain regions were involved in. Brain changes were found in pathways responsible for abnormal pain perception, including the classic trigemino-thalamo-cortical system and the lateral and medial pain systems. Dysfunction and maladaptive changes were also identified in the default mode network, the top-down antinociceptive periaqueductal gray-raphe magnus pathway, as well as the motor system. TMD patients displayed altered brain activations in response to both innocuous and painful stimuli compared with healthy controls. Additionally, evidence indicates that splint therapy can alleviate TMD-related symptoms by inducing functional brain changes. In summary, MRI research provides important novel insights into the altered neural manifestations underlying chronic pain in TMD.

Neural Pathways of Craniofacial Muscle Pain: Implications for Novel Treatments

Craniofacial muscle pain is highly prevalent in temporomandibular disorders but is difficult to treat. Enhanced understanding of neurobiology unique to craniofacial muscle pain should lead to the development of novel mechanism-based treatments. Herein, we review recent studies to summarize neural pathways of craniofacial muscle pain. Nociceptive afferents in craniofacial muscles are predominantly peptidergic afferents enriched with TRPV1. Signals from peripheral glutamate receptors converge onto TRPV1, leading to mechanical hyperalgesia. Further studies are needed to clarify whether hyperalgesic priming in nonpeptidergic afferents or repeated acid injections also affect craniofacial muscle pain. Within trigeminal ganglia, afferents innervating craniofacial muscles interact with surrounding satellite glia, which enhances the sensitivity of the inflamed neurons as well as nearby uninjured afferents, resulting in hyperalgesia and ectopic pain originating from adjacent orofacial tissues. Craniofacial muscle afferents project to a wide area within the trigeminal nucleus complex, and central sensitization of medullary dorsal horn neurons is a critical factor in muscle hyperalgesia related to ectopic pain and emotional stress. Second-order neurons project rostrally to pathways associated with affective pain, such as parabrachial nucleus and medial thalamic nucleus, as well as sensory-discriminative pain, such as ventral posteromedial thalamic nuclei. Abnormal endogenous pain modulation can also contribute to chronic muscle pain. Descending serotonergic circuits from the rostral ventromedial medulla facilitate activation of second-order neurons in the trigeminal nucleus complex, which leads to the maintenance of mechanical hyperalgesia of inflamed masseter muscle. Patients with temporomandibular disorders exhibit altered brain networks in widespread cortical and subcortical regions. Recent development of methods for neural circuit manipulation allows silencing of specific hyperactive neural circuits. Chemogenetic silencing of TRPV1-expressing afferents or rostral ventromedial medulla neurons attenuates hyperalgesia during masseter inflammation. It is likely, therefore, that further delineation of neural circuits mediating craniofacial muscle hyperalgesia potentially enhances treatment of chronic muscle pain conditions.

A comparative clinical study of arthrogenous versus myogenous temporomandibular disorder in patients presenting with Costen's syndrome

Objective: Costen's syndrome involves otoneurological and sinonasal symptoms associated with temporomandibular disorder (TMD). The current study compared the symptoms related to Costen's syndrome in patients with arthrogenous versus myogenous TMD.Methods: The study involved 294 consecutive patients with TMD, prospectively examined over a period of 6 months. These were stratified into 180 patients with arthrogenous TMD and 114 patients with myogenous TMD. A questionnaire and examination protocol was applied for each patient.Results: Sinonasal symptoms were more common in the arthrogenous group (p = .001), whereas, hearing loss and vertigo were more common in the myogenous group (p = .001).Conclusion: The current study provides support for central nervous system neuroplastic changes in the genesis of Costen's syndrome symptoms.

Reduced corticostriatal functional connectivity in temporomandibular disorders

Although temporomandibular disorders (TMD) have been associated with abnormal gray matter volumes in cortical areas and in the striatum, the corticostriatal functional connectivity (FC) of patients with TMD has not been studied. Here, we studied 30 patients with TMD and 20 healthy controls that underwent clinical evaluations, including Helkimo indices, pain assessments, and resting-state functional magnetic resonance imaging scans. The FCs of the striatal regions with the other brain areas were examined with a seed-based approach. As seeds, we used the dorsal caudate, ventral caudate/nucleus accumbens, dorsal caudal putamen, and ventral rostral putamen regions. Voxel-wise comparisons with controls revealed that the patients with TMD exhibited reduced FCs in the ventral corticostriatal circuitry, between the ventral striatum and ventral frontal cortices, including the anterior cingulate cortex and anterior insula; in the dorsal corticostriatal circuitry, between the dorsal striatum and the dorsal cortices, including the precentral gyrus and supramarginal gyrus; and also within the striatum. Additionally, we explored correlations between the reduced corticostriatal FCs and clinical measurements. These results directly supported the hypothesis that TMD is associated with reduced FCs in brain corticostriatal networks and that these reduced FCs may underlie the deficits in motor control, pain processing, and cognition in TMD. Our findings may contribute to the understanding of the etiologies and pathologies of TMD.