Effects of continuous theta-burst stimulation of the primary motor and secondary somatosensory areas on the central processing and the perception of trigeminal nociceptive input in healthy volunteers

Distinct neural mechanisms for action access and execution in the human brain: insights from an fMRI study

Goal-directed actions are fundamental to human behavior, whereby inner goals are achieved through mapping action representations to motor outputs. The left premotor cortex (BA6) and the posterior portion of Broca's area (BA44) are two modulatory poles of the action system. However, how these regions support the representation-output mapping within the system is not yet understood. To address this, we conducted a finger-tapping functional magnetic resonance imaging experiment using action categories ranging from specific to general. Our study found distinct neural behaviors in BA44 and BA6 during action category processing and motor execution. During access of action categories, activity in a posterior portion of BA44 (pBA44) decreased linearly as action categories became less specific. Conversely, during motor execution, activity in BA6 increased linearly with less specific categories. These findings highlight the differential roles of pBA44 and BA6 in action processing. We suggest that pBA44 facilitates access to action categories by utilizing motor information from the behavioral context while the premotor cortex integrates motor information to execute the selected action. This finding enhances our understanding of the interplay between prefrontal cortical regions and premotor cortex in mapping action representation to motor execution and, more in general, of the cortical mechanisms underlying human behavior.

A systematic review of the neurobiological effects of theta-burst stimulation (TBS) as measured using functional magnetic resonance imaging (fMRI)

Theta burst stimulation (TBS) is associated with the modulation of a range of clinical, cognitive, and behavioural outcomes, but specific neurobiological effects remain somewhat unclear. This systematic literature review investigated resting-state and task-based functional magnetic resonance imaging (fMRI) outcomes post-TBS in healthy human adults. Fifty studies that applied either continuous-or intermittent-(c/i) TBS, and adopted a pretest-posttest or sham-controlled design, were included. For resting-state outcomes following stimulation applied to motor, temporal, parietal, occipital, or cerebellar regions, functional connectivity generally decreased in response to cTBS and increased in response to iTBS, though there were some exceptions to this pattern of response. These findings are mostly consistent with the assumed long-term depression (LTD)/long-term potentiation (LTP)-like plasticity effects of cTBS and iTBS, respectively. Task-related outcomes following TBS were more variable. TBS applied to the prefrontal cortex, irrespective of task or state, also produced more variable responses, with no consistent patterns emerging. Individual participant and methodological factors are likely to contribute to the variability in responses to TBS. Future studies assessing the effects of TBS via fMRI must account for factors known to affect the TBS outcomes, both at the level of individual participants and of research methodology.

Modulation of somatosensation by transcranial magnetic stimulation over somatosensory cortex: a systematic review

Over the last three decades, transcranial magnetic stimulation (TMS) has gained popularity as a tool to modulate human somatosensation. However, the effects of different stimulation types on the multiple distinct subdomains of somatosensation (e.g., tactile perception, proprioception and pain) have not been systematically compared. This is especially notable in the case of newer theta-burst stimulation protocols now in widespread use. Here, we aimed to systematically and critically review the existing TMS literature and provide a complete picture of current knowledge regarding the role of TMS in modulating human somatosensation across stimulation protocols and somatosensory domains. Following the PRISMA guidelines, fifty-four studies were included in the current review and were compared based on their methodologies and results. Overall, findings from these studies provide evidence that different types of somatosensation can be both disrupted and enhanced by targeted stimulation of specific somatosensory areas. Some mixed results, however, were reported in the literature. We discussed possible reasons for these mixed results, methodological limitations of existing investigations, and potential avenues for future research.

Analgesic Electrical Stimulation Combined with Wrist-Ankle Acupuncture Reduces the Cortical Response to Pain in Patients with Myofasciitis: A Randomized Clinical Trial

OBJECTIVE

Transcutaneous electrical nerve stimulation (TENS) based on wrist-ankle acupuncture has been shown to relieve pain levels in patients with myofascial pain syndrome (MPS). However, its efficacy is highly subjective. The purpose of this study was to evaluate the feasibility and effectiveness of TENS based on wrist-ankle acupuncture for pain management in patients with MPS from the perspective of cerebral cortex hemodynamics.

DESIGN, SETTING, PARTICIPANTS AND INTERVENTIONS

We designed a double-blind, randomized, controlled clinical trial. Thirty-one male patients with MPS were randomly assigned to two parallel groups. The experimental group (n = 16) received TENS based on wrist-ankle acupuncture for analgesic treatment, while the control group (n = 15) did not. The pain was induced by mechanically pressurized at acupoint Jianjing. The multichannel functional near-infrared spectroscopy (fNIRS) equipment was utilized for measuring oxyhemoglobin (HbO) levels in the cerebral cortex during the tasks.

RESULTS

After the intervention, visual analog scale (VAS), the activation degree and activation area of pain perception cortices were significantly reduced in the experimental group compared to the baseline values (P < .05). Particularly, Frontopolar Area (FPA), and Dorsolateral Prefrontal Cortex (DLPFC) are highly involved in the pain process and pain modulation.

CONCLUSION

Compared to no intervention, TENS based on wrist-ankle acupuncture can be effective in relieving pain in patients with MPS in terms of cerebral cortical hemodynamics. However, further studies are necessary to quantify the analgesic effect in terms of cerebral hemodynamics and brain activation.

Altered brain activity and functional connectivity in migraine without aura during and outside attack

BACKGROUND

Migraine is commonly seen as a cyclic disorder with variable cortical excitability at different phases. Herein, we investigated the cortical excitability in migraine without aura patients during an attack (MWoA-DA) and interictal period (MWoA-DI) and further explored the functional connectivity (FC) in brain regions with cortical excitability abnormalities in patients.

METHODS

Seven MWoA-DA patients, twenty-seven MWoA-DI patients, and twenty-nine healthy controls (HC) underwent resting-state functional magnetic resonance imaging (rs-fMRI) scan. The amplitude of low-frequency fluctuations (ALFF) was assessed to identify spontaneous brain activity. Then, brain regions showing significant differences across groups were identified as regions of interest (ROI) in FC analysis.

RESULTS

Compared with MWoA-DI patients and HC, the ALFF in the trigeminocervical complex (TCC) was higher in the MWoA-DA patients. Decreased FC in MWoA-DA patients was found between TCC and left postcentral gyrus compared with MWoA-DI patients. Compared with HC, ALFF was lower in the right cuneus but higher in the right rolandic operculum of MWoA-DI patients. Additionally, the ALFF in the right cuneus was negatively correlated with the Migraine Disability Assessment Scale (MIDAS) in MWoA-DI patients.

CONCLUSIONS

The trigeminovascular system and impairments in descending pain modulatory pathways participate in the pathophysiology of migraine during the ictal period. The defense effect exists in the interictal phase, and the dysfunction in the cuneus may be related to the disease severity. This dynamic change in different brain regions could deepen our understanding of the physiopathology underlying migraine.

Treatment of postoperative delirium with continuous theta burst stimulation: study protocol for a randomised controlled trial

INTRODUCTION

Postoperative delirium is one of the most common postoperative complications among elderly patients (65 years old or older). However, there are no effective treatments for this condition. Recent research suggests that continuous theta burst stimulation (cTBS), a non-invasive brain stimulation, can reduce pain level, improve cognitive function and affective symptoms in multiple diseases or dysfunctions, including anxiety disorders, major depressive disorder, sleep disorders and pain. But the potential benefits of cTBS in reducing postoperative delirium have not been investigated. Therefore, we propose determining whether cTBS can prevent and/or treat postoperative delirium in senior patients.

METHODS AND ANALYSIS

The study will be a double-blind, randomised controlled trial. Participants (65 years old or older) undergoing scheduled orthopaedic surgery (≥2 hours, general anaesthesia) will be randomised to receive either cTBS or sham stimulation with a focal figure-of-eight coil over the right dorsolateral prefrontal cortex at 80% of the resting motor threshold. Every patient will receive 2-3 sets of stimulations during postoperative days (40 s per session, 3 sessions per set, 1 set per day). Participants will be assessed twice daily by a research assistant blinded to allocation. The primary outcome will be the incidence of postoperative delirium measured by the Confusion Assessment Method on postoperative days 1, 2 and 3. The secondary outcomes will be the severity and duration of postoperative delirium, cognitive function, pain, sleep quality, activities of daily living, length of hospital stay, discharge-to-facility or home, and rate of complication and mortality during the hospital stay.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the ethics committee of Shanghai 10th People's Hospital. The principal investigator will submit a research progress report to the ethics committee regularly. All participants will provide written informed consent. Study results will be published in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NCT04661904.

Central encoding of the strength of intranasal chemosensory trigeminal stimuli in a human experimental pain setting

An important measure in pain research is the intensity of nociceptive stimuli and their cortical representation. However, there is evidence of different cerebral representations of nociceptive stimuli, including the fact that cortical areas recruited during processing of intranasal nociceptive chemical stimuli included those outside the traditional trigeminal areas. Therefore, the aim of this study was to investigate the major cerebral representations of stimulus intensity associated with intranasal chemical trigeminal stimulation. Trigeminal stimulation was achieved with carbon dioxide presented to the nasal mucosa. Using a single-blinded, randomized crossover design, 24 subjects received nociceptive stimuli with two different stimulation paradigms, depending on the just noticeable differences in the stimulus strengths applied. Stimulus-related brain activations were recorded using functional magnetic resonance imaging with event-related design. Brain activations increased significantly with increasing stimulus intensity, with the largest cluster at the right Rolandic operculum and a global maximum in a smaller cluster at the left lower frontal orbital lobe. Region of interest analyses additionally supported an activation pattern correlated with the stimulus intensity at the piriform cortex as an area of special interest with the trigeminal input. The results support the piriform cortex, in addition to the secondary somatosensory cortex, as a major area of interest for stimulus strength-related brain activation in pain models using trigeminal stimuli. This makes both areas a primary objective to be observed in human experimental pain settings where trigeminal input is used to study effects of analgesics.

Evidence-based guidelines on the therapeutic use of repetitive transcranial magnetic stimulation (rTMS): An update (2014-2018)

A group of European experts reappraised the guidelines on the therapeutic efficacy of repetitive transcranial magnetic stimulation (rTMS) previously published in 2014 [Lefaucheur et al., Clin Neurophysiol 2014;125:2150-206]. These updated recommendations take into account all rTMS publications, including data prior to 2014, as well as currently reviewed literature until the end of 2018. Level A evidence (definite efficacy) was reached for: high-frequency (HF) rTMS of the primary motor cortex (M1) contralateral to the painful side for neuropathic pain; HF-rTMS of the left dorsolateral prefrontal cortex (DLPFC) using a figure-of-8 or a H1-coil for depression; low-frequency (LF) rTMS of contralesional M1 for hand motor recovery in the post-acute stage of stroke. Level B evidence (probable efficacy) was reached for: HF-rTMS of the left M1 or DLPFC for improving quality of life or pain, respectively, in fibromyalgia; HF-rTMS of bilateral M1 regions or the left DLPFC for improving motor impairment or depression, respectively, in Parkinson's disease; HF-rTMS of ipsilesional M1 for promoting motor recovery at the post-acute stage of stroke; intermittent theta burst stimulation targeted to the leg motor cortex for lower limb spasticity in multiple sclerosis; HF-rTMS of the right DLPFC in posttraumatic stress disorder; LF-rTMS of the right inferior frontal gyrus in chronic post-stroke non-fluent aphasia; LF-rTMS of the right DLPFC in depression; and bihemispheric stimulation of the DLPFC combining right-sided LF-rTMS (or continuous theta burst stimulation) and left-sided HF-rTMS (or intermittent theta burst stimulation) in depression. Level A/B evidence is not reached concerning efficacy of rTMS in any other condition. The current recommendations are based on the differences reached in therapeutic efficacy of real vs. sham rTMS protocols, replicated in a sufficient number of independent studies. This does not mean that the benefit produced by rTMS inevitably reaches a level of clinical relevance.