Biology subjects

Seminowicz, D. A.

Publications and source records attributed to Seminowicz, D. A..

At least 19 recordsLinked to original sources

bioRxiv2026

Sex-dependent changes in insular cortex connectivity in a rat model of comorbid pain

Temporomandibular disorder (TMD) and irritable bowel syndrome (IBS) are two highly comorbid, nociplastic pain conditions that belong to a broader group of commonly co-occurring chronic pain conditions. Most of these chronic overlapping pain conditions (COPCs), including TMD and IBS, disproportionately affect females and are highly stress sensitive. Our previous study illustrated sex differences in brain activity during colorectal distension specific to our model of comorbid pain hypersensitivity (CPH), in which masseter muscle inflammation followed by restraint stress elicits IBS-like visceral hypersensitivity. Since insular cortex (Ins) activity increased in female CPH rats only and abnormal Ins activity has been identified in TMD and IBS patients, we sought to characterize patterns of Ins-based functional connectivity (FC) by performing functional MRI (fMRI) scans at baseline, 1 week, and 7 weeks post-injury/stress in groups of male and female Sprague-Dawley rats randomized to the following conditions: CPH, stress-induced hypersensitivity (SIH), Complete Freunds Adjuvant (CFA)-induced masseter muscle inflammation, and naive. CPH females displayed extensive Ins FC with brain regions in the cortex and limbic system, including the thalamus. Compared to CPH males, CPH females showed robust insular-thalamo connectivity at week seven, a time point where visceral hypersensitivity and referred pain-like behavior persists in CPH females but not males. This trend is also apparent in CPH females week seven versus week one Ins FC, whereas CPH males tend to decrease Ins FC broadly. These findings potentially suggest sensitization within the insular-thalamo and -cortical networks in CPH females, warranting future investigation of Ins circuit involvement in comorbid pain.

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bioRxiv2025

Developing a model of temporomandibular disorder in the common marmoset using nerve growth factor

Developing an animal model that more closely represents the human multidimensional pain experience is an important step towards addressing the current chronic pain crisis. The common marmoset has potential as this model species given its biological, neurological and phylogenetic similarity to humans. Here, we developed a model of myofascial temporomandibular disorder (TMD) in the marmoset by injecting nerve growth factor (NGF) into the superficial masseter. Following injection, animals showed reduced mechanical withdrawal thresholds at 5 g and 10 g doses of NGF and changes in circadian rhythm and feeding initiation following injection of 10 g of NGF. Animals did not show evidence of jaw dysfunction, masticatory alterations, or grimace during novel behavioural assays. The model is transient, with pain resolution occurring approximately 7 days after onset, which allows for repeated testing on the same animal. This same NGF-TMD model has been previously validated in rodents and humans and presents an opportunity for forward and reverse translation to examine mechanisms, develop relevant pain assessment tools, and ultimately test novel treatments for TMD and other musculoskeletal pain conditions. New & NoteworthyWe developed a long-lasting but transient ([~]7 days) model of myofascial temporomandibular disorder pain in marmosets. Mechanical hypersensitivity and changes to circadian activity and spontaneous eating behaviours were observed. There was no evidence of jaw dysfunction, altered food preference or changes in grimace. The NGF-TMD model can be translated to the marmoset with the potential for investigating mechanisms and novel interventions for TMD.

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bioRxiv2025

Transcranial magnetic stimulation induced pupil dilations can serve as a cortical excitability measure

The application of non-invasive brain stimulation (NIBS) often relies on proxy estimates of cortical excitability (CE), such as the resting motor threshold (rMT), measured through transcranial magnetic stimulation (TMS). However, estimating the rMT is not always possible, as it requires an intact corticospinal pathway for neural signals to travel from the cortex to the periphery. To broaden the application of NIBS there is a need for additional CE measures. In three experiments combining TMS, transcranial direct current stimulation (tDCS), and eye-tracking, we measured TMS-induced pupil dilations as a potential CE proxy. We present Bayesian evidence (Experiment 1: BF > 9; Experiment 2: BF > 46; Experiment 3: BFs > 6) that TMS-induced pupil dilations serve as an objective CE proxy, with larger pupil size reflecting higher CE. We also show that these effects are not due to auditory, muscle, or sensory confounds. The introduction of this novel measure paves the way for a deeper understanding of CE by enabling objective NIBS measures beyond the motor cortex. Moving away from the reliance on the motor cortex would allow NIBS research and therapy to become more inclusive, allowing access to populations that are affected by damage along the corticospinal pathway.

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bioRxiv2025

The human claustrum initiates networks for externally and internally driven task demands.

Cognitive control is believed to arise from interactions among multiple brain networks depending on task demands. Although several debilitating neuropsychiatric disorders are characterized by cognitive network dysfunction, the neural circuit mechanisms supporting task-dependent network activation are largely unknown. Because the claustrum possesses widespread connections with cortex and can synchronize distant cortical regions, we tested whether the claustrum activates task-dependent network states using fMRI during working memory (n = 420) and autobiographical memory (n = 35), tasks which elicit opposing responses from key cognitive control networks. In both tasks, the claustrum exhibited increased activity and excitatory influence on task-associated cognitive control network nodes, with corroborating underlying structural connectivity. The claustrum also displayed stronger excitatory effective connectivity during task performance and greater structural connectivity with task-related network nodes than regions prominently implicated in directing network states--the anterior insula and pulvinar. These findings establish a role for the claustrum in initiating network states for cognitive control. SignificanceCognitive functioning is supported by large-scale networks across the brain. Yet, the neural circuit mechanisms supporting task-dependent network activation are largely unknown. Circuit analyses using human functional and structural neuroimaging in this study found that the claustrum, a subcortical nucleus, activates during multiple cognitive tasks eliciting a wide range of network states, possesses strong anatomical connections with cognitive control network nodes, and exerts excitatory influence on task-associated network regions. These results establish the claustrum as a network activator subserving cognitive control.

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bioRxiv2025

Resting State Functional Connectivity of the Marmoset Claustrum

The common marmoset (Callithrix jacchus) has been recently developed as a nonhuman primate model useful for studying behaviour, neurology, and higher-level cognitive processes considering their phylogenetic proximity to humans. Here, we investigated the resting state functional connectivity (RSFC) of the marmoset claustrum, a small, highly connected subcortical structure. Using an open resource of 234 functional MRI scans from awake marmosets, we found claustrum connectivity to the prefrontal cortex, posterior parietal cortex, temporal cortices, cingulate cortex, sensory cortices, limbic areas, basal ganglia, and cerebellum. We also found strong functional connectivity to regions and hubs involved in marmoset resting state networks. These findings demonstrate marmoset claustrum RSFC similar to previous human and rodent studies and validate the integration of marmosets into claustrum research.

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bioRxiv2025

The Thermal Grill Elicits Central Sensitization

The thermal grill, in which innocuous warm and cool stimuli are interlaced, can produce a paradoxical burning pain sensation--the thermal grill illusion (TGI). While the mechanisms underlying TGI remain unclear, prominent theories point to spinal dorsal horn integration of innocuous thermal inputs to elicit pain. It remains unknown whether the TGI activates peripheral nociceptors, or solely thermosensitive afferents integrated within the spinal cord. Different types of sensitization have established mechanisms and can inform TGI mechanisms: if the TGI elicits (1) primary hyperalgesia, peripheral nociceptors are likely be activated; (2) secondary hyperalgesia without primary hyperalgesia, spinal integration is likely required; and (3) brush allodynia, wide-dynamic range neurons could be involved in mediating the TGI. Here, we determine whether the TGI elicits primary hyperalgesia, secondary hyperalgesia or brush allodynia. Fifty-two participants underwent individually calibrated phasic thermal grill stimulation. We found that the calibrated TGI elicited primary hyperalgesia, but only in participants with component temperatures in the noxious range (<19{degrees}C and >41{degrees}C). The TGI also elicited secondary hyperalgesia, even in participants with strictly innocuous thermal inputs. No participants developed brush allodynia. We observed sex differences in primary hyperalgesia: only males exhibited thermal grill-induced primary hyperalgesia. These findings suggest that the TGI is integrated in the spinal dorsal horn, potentially mediated by heat-pinch-cold (HPC) neurons, and, to some degree, by primary nociceptive afferents in males. This study shows that the calibrated TGI may have sex-dependent mechanisms and determines that HPC cells are involved in the illusory sensation of pain from innocuous thermal inputs.

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bioRxiv2024

The effect of prolonged elbow pain and rTMS on cortical inhibition: A TMS-EEG study

IntroductionRecent studies using combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) have shown that pain leads to an increase in the N45 peak of the TMS-evoked potential (TEP), which is mediated by GABAergic inhibition. Conversely, 10Hz repetitive TMS (10Hz-rTMS), which provides pain relief, reduces the N45 peak. However, these studies used brief pain stimuli (lasting minutes), limiting their clinical relevance. The present study determined the effect of pain and 10Hz-rTMS on the N45 peak in a prolonged pain model (lasting several days) induced by nerve growth factor (NGF) injection to the elbow muscle. Materials and MethodsExperiment 1: TEPs were measured in 22 healthy participants on Day 0 (pre-NGF), Day 2 (peak pain), and Day 7 (pain resolution). Experiment 2: We examined the effect of 5 days of active (n=16) or sham (n=16) rTMS to the left primary motor cortex (M1) on the N45 peak during prolonged NGF-induced pain, with TEPs measured on Day 0 and Day 4 (post-rTMS). ResultsExperiment 1: While no overall change in the N45 peak was seen, a correlation emerged between higher pain severity on Day 2 and a larger increase in the N45 peak. Experiment 2: Active rTMS reduced the N45 peak on Day 4 vs. Day 0, with no effect in the sham group. ConclusionOur findings suggest that (i) higher pain severity correlates with an increase in the N45 peak, and (ii) rTMS decreases cortical inhibition in a model of prolonged experimental pain. This study extends previous research by demonstrating a link between pain perception and cortical inhibition within a prolonged pain context.

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bioRxiv2024

The human claustrum activates across multiple cognitive tasks

Cognitive control, the ability to manage information during purposeful actions, is crucial for everyday functioning and can become impaired in a variety of neuropsychiatric disorders. The claustrum, a subcortical brain structure, has recently been implicated in functional mechanisms underlying cognitive control. A current theory on the claustrums function, the Network Instantiation in Cognitive Control (NICC) model, proposes that the claustrum acts as a cortical network hub synchronizing distant parts of the brain to optimize task performance across cognitive domains. Testing this in this study, we examined the claustrum signal within a dataset (n = 55) that includes functional MRI (fMRI) of healthy participants engaged in four well-established cognitive tasks: the Stroop task, AX-continuous performance task (AX-CPT), cued task-switching, and Sternberg working memory task. Bilateral claustrum activation was observed during certain conditions and trial phases of all four tasks, particularly during active use of cognitive control, and coinciding with task-positive cortical network activations. These findings provide further support for the NICC model of claustrum function, demonstrating claustrum activation across multiple cognitive tasks, and potentially paving the way for new insights into how cognitive processes can become compromised in neuropsychiatric disorders.

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bioRxiv2024

It's the Sound not the Pulse: Peripheral Magnetic Stimulation Reduces Central Sensitization through Auditory Modulatory Effects

Repetitive peripheral magnetic stimulation (rPMS) is a non-pharmacological, non-invasive analgesic modality with limited side effects. However, there is a paucity of controlled studies demonstrating its efficacy compared to existing pain management tools. Here, in an initial sample of 100 healthy participants (age 18-40), we compared the analgesic efficacy of two rPMS stimulation protocols--continuous theta burst stimulation (ctbPMS) and intermittent TBS (itbPMS)--against transcutaneous electric nerve stimulation (TENS), a peripheral stimulation technique that is commonly used for pain management. We also included a sham rPMS protocol where participants heard the sound of rPMS stimulation while the coil was placed over their arm, but received no peripheral stimulation. We hypothesized that itbPMS and ctbPMS--but not sham--would reduce pain intensity, pain unpleasantness, and secondary hyperalgesia evoked by a phasic heat pain (PHP) paradigm on the volar forearm with similar efficacy to TENS. Neither rPMS nor TENS reduced reported pain intensity or unpleasantness (p>0.25). However, ctbPMS and itbPMS significantly reduced the area of secondary hyperalgesia, whereas TENS did not (F3,96= 4.828, p= 0.004). Unexpectedly, sham rPMS, which involved auditory but no peripheral nerve stimulation, also significantly reduced secondary hyperalgesia compared to TENS. We performed a second study (n=32) to investigate auditory contributions to rPMS analgesia. Masking the rPMS stimulation sound with pink noise eliminated its analgesic effect on secondary hyperalgesia (p=0.5). This is the first study to show that the analgesic properties of rPMS in acute experimental pain may be largely attributed to its auditory component rather than peripheral nerve stimulation.

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bioRxiv2024

Peak alpha frequency is not significantly altered by five days of experimental pain and repetitive transcranial stimulation of the left dorsolateral prefrontal cortex

Repetitive transcranial magnetic stimulation (rTMS) holds promise as a non-invasive pain treatment. Given the link between individual peak alpha frequency (PAF) of resting-state electroencephalographic recordings and pain sensitivity, and the potential for rTMS to modulate PAF, we investigated these relationships through a secondary analysis of established rTMS-induced analgesia in an experimental model of sustained muscle pain. In a randomised, single-blind, sham-controlled experiment, 30 healthy adults underwent either active (n=15) or sham (n=15) high-frequency rTMS (20 min) to the left dorsolateral prefrontal cortex for five consecutive days following induction of sustained experimental pain by nerve growth factor (NGF) injected into the right extensor carpi radialis brevis muscle. The pain intensity was assessed daily for 14 days on a numerical rating scale (NRS). PAF of the resting state electroencephalography (5 min) was assessed before and one day after the five rTMS treatment days. The pre-registered analysis revealed no significant changes in PAF following five consecutive days of active (from 9.90{+/-}0.39 Hz to 9.95{+/-}0.38 Hz) or sham (from 9.86{+/-}0.44 Hz to 9.81{+/-}0.35 Hz) rTMS, suggesting that the impact of rTMS on NGF-induced pain is independent of PAF modulation. However, exploratory analysis indicated an association between a larger absolute difference in baseline PAF to 10 Hz (i.e. the rTMS frequency) and higher NRS pain ratings at Day 5 in participants receiving active rTMS. This suggests rTMS is more efficient when delivered close to individual PAF or for those with PAF around 10 Hz, necessitating further exploration of PAFs role in rTMS-induced pain relief.

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bioRxiv2024

A 5-day course of rTMS before pain onset ameliorates future pain and increases sensorimotor peak alpha frequency

Repetitive transcranial magnetic stimulation (rTMS) has shown promise as an intervention for pain. An unexplored research question is whether the delivery of rTMS prior to pain onset might protect against a future episode of prolonged pain. The present study aimed to determine i) whether 5 consecutive days of rTMS delivered prior to experimentally-induced prolonged jaw pain could reduce future pain intensity and ii) whether any effects of rTMS on pain were mediated by changes in corticomotor excitability (CME) and/or sensorimotor peak alpha frequency (PAF). On each day from Day 0-4, forty healthy individuals received a single session of active (n = 21) or sham (n = 19) rTMS over the left primary motor cortex. PAF and CME were assessed on Day 0 (before rTMS) and Day 4 (after rTMS). Prolonged pain was induced via intramuscular injection of nerve growth factor (NGF) in the right masseter muscle after the final rTMS session. From Days 5-25, participants completed twice-daily electronic dairies including pain on chewing and yawning (primary outcomes), as well as pain during other activities (e.g. talking), functional limitation in jaw function and muscle soreness (secondary outcomes). Compared to sham, individuals who received active rTMS subsequently experienced lower pain on chewing and yawning. Although active rTMS increased PAF, the effects of rTMS on pain were not mediated by changes in PAF or CME. This study is the first to show that rTMS delivered prior to pain onset can protect against future pain and associated functional impairment. Thus, rTMS may hold promise as a prophylactic intervention for persistent pain.

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bioRxiv2024

POSTERIOR-SUPERIOR INSULA REPETITIVE TRANSCRANIAL MAGNETIC STIMULATION REDUCES EXPERIMENTAL TONIC PAIN AND PAIN-RELATED CORTICAL INHIBITION IN HUMANS

High frequency repetitive transcranial magnetic stimulation (rTMS) to the posterosuperior insula (PSI) may produce analgesic effects. However, the neuroplastic changes behind PSI-rTMS analgesia remain poorly understood. The present study aimed to determine whether tonic capsaicin-induced pain and cortical inhibition (indexed using TMS-electroencephalography) are modulated by PSI-rTMS. Twenty healthy volunteers (10 females) attended two sessions randomized to active or sham rTMS. Experimental pain was induced by capsaicin administered to the forearm for 90 minutes, with pain ratings collected every 5 minutes. Left PSI-rTMS was delivered (10Hz, 100 pulses per train, 15 trains) [~]50 minutes post-capsaicin administration. TMS-evoked potentials (TEPs) and thermal sensitivity were assessed at baseline, during capsaicin pain prior to rTMS and after rTMS. Bayesian evidence of reduced pain scores and increased heat pain thresholds were found following active rTMS, with no changes occurring after sham rTMS. Pain (prior to active rTMS) led to an increase in the frontal negative peak [~]45 ms (N45) TEP relative to baseline. Following active rTMS, there was a decrease in the N45 peak back to baseline levels. In contrast, following sham rTMS, the N45 peak was increased relative to baseline. We also found that the reduction in pain NRS scores following active vs. sham rTMS was partially mediated by decreases in the N45 peak. These findings provide evidence of the analgesic effects of PSI-rTMS and suggest that the TEP N45 peak is a potential marker and mediator of both pain and analgesia.

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bioRxiv2023

Phosphene and Motor Transcranial Magnetic Stimulation Thresholds Are Correlated: A Meta-Analytic Investigation

Transcranial magnetic stimulation (TMS) is commonly delivered at an intensity defined by the resting motor threshold (rMT), which is thought to represent cortical excitability, even if the TMS target area falls outside of the motor cortex. This approach rests on the assumption that cortical excitability, as measured through the motor cortex, represents a global measure of excitability. Another common approach to measure cortical excitability relies on the phosphene threshold (PT), measured through the visual cortex of the brain. However, it remains unclear whether either estimate can serve as a singular measure of global cortical excitability. If PT and rMT indeed reflect global cortical excitability, they should be correlated. To test this, we systematically identified previous studies that measured PT and rMT to calculate an overall correlation between the two estimates. Our results, based on 16 effect sizes from eight studies, indicated that PT and rMT are correlated ({rho} = .4), and thus one measure could potentially serve as a global cortical excitability measure. Three exploratory meta-analyses revealed that the strength of the correlation is affected by different methodologies, and that PT intensities are higher than rMT. Evidence for a PT-rMT correlation remained robust across all analyses. Further research is necessary for an in-depth understanding of how cortical excitability is reflected through TMS.

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bioRxiv2023

Can non-invasive brain stimulation modulate peak alpha frequency in the human brain? A systematic review and meta-analysis

Peak alpha frequency, the dominant oscillatory frequency within the alpha range (8-12 Hz), is associated with cognitive function and several neurological conditions, including chronic pain. Manipulating PAF could offer valuable insight into the relationship between PAF and various functions and conditions and provide new treatment avenues. This systematic review aimed to comprehensively synthesise effects of non-invasive brain stimulation (NIBS) on PAF speed. Relevant studies assessing PAF pre- and post-NIBS in healthy adults were identified through systematic searches of electronic databases (Embase, PubMed, PsychINFO, Scopus, The Cochrane Library) and trial registers. The Cochrane risk-of-bias tool was employed for assessing study quality. Quantitative analysis was conducted through pairwise meta-analysis when possible; otherwise, qualitative synthesis was performed. The review protocol was registered with PROSPERO (CRD42020190512) and the Open Science Framework (https://osf.io/2yaxz/). Eleven NIBS studies were included, all with a low risk-of-bias, comprising seven transcranial alternating current stimulation (tACS), three repetitive transcranial magnetic stimulation (rTMS), and one transcranial direct current stimulation (tDCS) study. Meta-analysis of active tACS conditions (eight conditions from five studies) revealed no significant effects on PAF (mean difference [MD] = -0.12, 95% CI = -0.32 to 0.08, p = 0.24). Qualitative synthesis provided no evidence that tDCS altered PAF and moderate evidence for transient increases in PAF with 10 Hz rTMS. There is limited evidence that NIBS can modulate PAF, and existing evidence does not demonstrate robust effects. Further studies employing standardised stimulation protocols are necessary to determine the potential of NIBS to modulate PAF.

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bioRxiv2023

Pathological claustrum activity drives aberrant cognitive network processing in human chronic pain

Aberrant cognitive network activity and cognitive deficits are established features of chronic pain. However, the nature of cognitive network alterations associated with chronic pain and their underlying mechanisms require elucidation. Here, we report that the claustrum, a subcortical nucleus implicated in cognitive network modulation, is activated by acute painful stimulation and pain-predictive cues in healthy participants. Moreover, we discover pathological activity of the claustrum and a lateral aspect of the right dorsolateral prefrontal cortex (latDLPFC) in migraine patients. Dynamic causal modeling suggests a directional influence of the claustrum on activity in this latDLPFC region, and diffusion weighted imaging (DWI) verifies their structural connectivity. These findings advance understanding of claustrum function during acute pain and provide evidence of a possible circuit mechanism driving cognitive impairments in chronic pain.

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bioRxiv2023

Effects of nicotine compared to placebo gum on sensitivity to pain and mediating effects of peak alpha frequency

Recent research has linked individual peak alpha frequency (PAF) to pain sensitivity, but whether PAF alterations can influence pain remains unclear. Our study investigated the effects of nicotine on pain sensitivity and whether pain changes are mediated by PAF changes. In a randomised, double-blind, placebo-controlled experiment, 62 healthy adults (18-44 years) received either 4 mg nicotine (n=29) or placebo gum (n=33). Resting state EEG and pain ratings during prolonged heat and pressure models were collected before and after nicotine intake. The nicotine group showed a small decrease in heat-pain ratings compared to placebo group when controlling confounders, and a small increase in PAF across the scalp from pre- to post-gum, both with and without confounder adjustment. These effects were most pronounced in the central-parietal and right-frontal electrodes. However, mediation analysis did not support the notion that PAF changes mediate nicotines effects on pain sensitivity. While a growing body of literature supports a link between PAF and both acute and chronic pain, further work is needed to understand the mechanisms of this link.

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bioRxiv2023

Alterations in cortical excitability during pain: A combined TMS-EEG Study

Transcranial magnetic stimulation (TMS) has been used to examine inhibitory and facilitatory circuits during experimental pain and in chronic pain populations. However, current applications of TMS to pain have been restricted to measurements of motor evoked potentials (MEPs) from peripheral muscles. Here, TMS was combined with electroencephalography (EEG) to determine whether experimental pain could induce alterations in cortical inhibitory/facilitatory activity observed in TMS-evoked potentials (TEPs). In Experiment 1 (n = 29), multiple sustained thermal stimuli were administered to the forearm, with the first, second and third block of thermal stimuli consisting of warm but non-painful (pre-pain block), painful (pain block) and warm but non-painful (post-pain block) temperatures respectively. During each stimulus, TMS pulses were delivered while EEG (64 channels) was simultaneously recorded. Verbal pain ratings were collected between TMS pulses. Relative to pre-pain warm stimuli, painful stimuli led to an increase in the amplitude of the frontocentral negative peak [~]45ms post-TMS (N45), with a larger increase associated with higher pain ratings. Experiments 2 and 3 (n = 10 in each) showed that the increase in the N45 in response to pain was not due to changes in sensory potentials associated with TMS, or a result of stronger reafferent muscle feedback during pain. This is the first study to use combined TMS-EEG to examine alterations in cortical excitability in response to pain. These results suggest that the N45 TEP peak, which indexes GABAergic neurotransmission, is implicated in pain perception and is a potential marker of individual differences in pain sensitivity.

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bioRxiv2022

Intramuscular injection of nerve growth factor as a model of temporomandibular disorder: nature, time-course, and sex differences characterising the pain experience

BackgroundTemporomandibular disorder (TMD) is a common condition that frequently transitions to chronic symptoms. Experimental pain models that mimic the symptoms of clinical TMD may be useful in understanding the mechanisms, and sex differences, present in this disorder. Here we aimed to comprehensively characterise the nature and time-course of pain, functional impairment and hyperalgesia induced by repeated intramuscular injection of nerve growth factor (NGF) into the masseter muscle, and to investigate sex differences in the NGF-induced pain experience. Methods94 healthy individuals participated in a longitudinal observational study with 30-day follow-up. NGF was injected into the right masseter muscle on Day 0 and Day 2. Participants attended laboratory sessions to assess pain (Numerical Rating Scale; NRS), functional limitation (mouth opening distance, Jaw Functional Limitation Scale; JFLS) and mechanical sensitization (pressure pain thresholds; PPTs) on Days 0, 2 and 5 and completed twice daily electronic pain dairies from Day 0 to day 30. ResultsPeak pain averaged 2.0/10 (95 % CI: 1.6-2.4) at rest and 4.3/10 (95 % CI: 3.9-4.8) on chewing. Pain-free mouth opening distance reduced from 5.0 cm (95 % CI: 4.8-5.1 cm) on Day 0 to 3.7 cm (95 % CI: 3.5-3.9 cm) on Day 5. The greatest reduction in PPTs was observed over the masseter muscle. Females experienced higher pain, greater functional impairment, and greater sensitivity to mechanical stimuli than males. ConclusionIntramuscular injection of NGF is a useful model with which to explore the mechanisms, and sex differences, present in clinical TMD.

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