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.
Abstract This study investigates the neural correlates underpinning response inhibition using a parametric ex‐Gaussian model of stop‐signal task performance, fit with hierarchical Bayesian methods, in a large healthy sample ( N = 156). The parametric model accounted for both stop‐signal reaction time (SSRT) and trigger failure (i.e., failures to initiate the inhibition process). The returned SSRT estimate (SSRT EXG3 ) was attenuated by ≈65 ms compared to traditional nonparametric SSRT estimates (SSRT int ). The amplitude and latency of the N1 and P3 event‐related potential components were derived for both stop‐success and stop‐failure trials and compared to behavioral estimates derived from traditional (SSRT int ) and parametric (SSRT EXG3 , trigger failure) models. Both the fronto‐central N1 and P3 peaked earlier and were larger for stop‐success than stop‐failure trials. For stop‐failure trials only, N1 peak latency correlated with both SSRT estimates as well as trigger failure and temporally coincided with SSRT EXG3 , but not SSRT int . In contrast, P3 peak and onset latency were not associated with any behavioral estimates of inhibition for either trial type. While the N1 peaked earlier for stop‐success than stop‐failure trials, this effect was not found in poor task performers (i.e., high trigger failure/slow SSRT). These findings are consistent with attentional modulation of both the speed and reliability of the inhibition process, but not for poor performers. Together with the absence of any P3 onset latency effect, our findings suggest that attentional mechanisms are important in supporting speeded and reliable inhibition processes required in the stop‐signal task.
ABSTRACT BACKGROUND Determining the mechanistic causes of complex biopsychosocial health conditions such as low back pain (LBP) is challenging, and research is scarce. Cross-sectional studies demonstrate altered excitability and organisation of the primary somatosensory and primary motor cortex in people with acute and chronic LBP, however, no study has explored these mechanisms longitudinally or attempted to draw causal inferences. METHODS Prospective, longitudinal, cohort study including 120 people with an acute episode of LBP. Sensory evoked potential area measurements were used to assess primary and secondary somatosensory cortex excitability. Transcranial magnetic stimulation derived map volume was used to assess corticomotor excitability. Directed acyclic graphs identified variables potentially confounding the exposure-outcome relationship. The effect of acute-stage sensorimotor cortex excitability on six-month LBP outcome was estimated using multivariable regression modelling, with adjusted and unadjusted estimates reported. Sensitivity analyses were performed to explore the effect of unmeasured confounding and missing data. RESULTS Lower primary (OR = 2.08, 95% CI = 1.22 to 3.57) and secondary (OR = 2.56, 95% CI = 1.37 to 4.76) somatosensory cortex excitability in the acute stage of LBP increased the odds of developing chronic pain at six-month follow-up. This finding was robust to confounder adjustment and unmeasured confounding (E-Value = 2.24 & 2.58, respectively). Corticomotor excitability in the acute stage of LBP was associated with higher pain intensity at 6-month follow-up (B = −0.15, 95% CI: −0.28 to −0.02) but this association did not remain after confounder adjustment. CONCLUSION These data provide the first evidence that low somatosensory cortex excitability in the acute stage of LBP is a cause of chronic pain. Interventions designed to increase somatosensory cortex excitability in acute LBP may be relevant to the prevention of chronic pain.
Abstract Many pain biomarkers fail to move from discovery to clinical application, attributed to poor reliability and feasible classifications of at-risk individuals. Preliminary evidence has shown that higher pain sensitivity is associated with slow peak alpha frequency (PAF) and depression of corticomotor excitability (CME). The present study evaluated the reliability of these measures, specifically whether, over several days of pain, a) PAF remains stable and b) individuals show two stable and distinct CME responses: facilitation and depression. Seventy-five healthy participants were given an injection of nerve growth factor (NGF) into the right masseter muscle on Day 0 and Day 2, inducing sustained pain. Electroencephalography (EEG) to assess PAF and transcranial magnetic stimulation (TMS) to assess CME were recorded on Day 0, Day 2 and Day 5. PAF reliability was in the excellent range even without standard pre-processing and ∼2 minutes recording length. Moreover, two distinct and stable CME responses were demonstrated: facilitation and depression. These findings support the notion that PAF is a stable trait characteristic, with reliability unaffected by pain, and excellent reliability achievable with minimal pre-processing and ∼2 minutes recording, making it a readily translatable biomarker. Furthermore, the study showed novel evidence of two stable corticomotor adaptations to sustained pain. Overall, the study provides support for the reliability of PAF and CME as prospective cortical biomarkers.
Abstract Introduction: The primary motor cortex (M1) is a key brain region implicated in pain processing. Here, we present a protocol for a review that aims to synthesise and critically appraise the evidence for the effect of experimentalpain on M1 function. Methods/Analysis: A systematic review and meta-analysis will be conducted. Electronic databases will be searched using a predetermined strategy. Studies published before April 2020 that investigate the effects of experimentally induced pain on corticomotor excitability (CME) in healthy individuals will be included if they meet eligibility criteria. Study identification, data extraction andrisk of bias assessment will be conducted by two independent reviewers, with a third reviewer consulted for any disagreements. The primary outcomes will include group level changes in CME and intracortical, transcortical and sensorimotor modulators of CME. A separate analysis using individual data will also be conducted to explore individual differences in CME in response to experimental pain. The meta-analysis will consider the following factors: pain model (transient, tonic, transitional pain), type of painful tissue (cutaneous, musculoskeletal), time points of outcome measures(during or after recovery from pain) and localisation of pain(target area, control area). Discussion: This review will provide a comprehensive understanding of the mechanisms within M1 that mediate experimentally induced pain, both on a group and individual level. Registration Number: The systematic review is registered with the International Prospective Register of Systematic Reviews (#CRD42020173172)
Response inhibition refers to the cancelling of planned (or restraining of ongoing) actions and is required in much of our everyday life. Response inhibition appears to improve dramatically in early development and plateau in adolescence. The fronto-basal-ganglia network has long been shown to predict individual differences in the ability to enact response inhibition. In the current study, we examined whether developmental trajectories of fiber-specific white matter properties of the fronto-basal-ganglia network was predictive of parallel developmental trajectories of response inhibition. 138 children aged 9–14 completed the stop-signal task (SST). A subsample of 73 children underwent high-angular resolution diffusion MRI data for up to three time points. Performance on the SST was assessed using a parametric race modelling approach. White matter organization of the fronto-basal-ganglia circuit was estimated using fixel-based analysis. Contrary to predictions, we did not find any significant associations between maturational trajectories of fronto-basal-ganglia white matter and developmental improvements in SST performance. Findings suggest that the development of white matter organization of the fronto-basal-ganglia and development of stopping performance follow distinct maturational trajectories.
Transcranial magnetic stimulation (TMS) has been used to examine the 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 over the forearm, with the first, second and third block of stimuli consisting of warm but non-painful (pre-pain block), painful heat (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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