Inhibition of cortical somatosensory processing during and after low frequency peripheral nerve stimulation in humans

Peripheral Electrical Stimulation on Motor Function and Activities of Daily Living After Stroke: A Systematic Review and Network Meta-analysis

OBJECTIVE

To compare the effects of different peripheral electrical stimulation protocols and current frequencies for poststroke motor function and activities of daily living.

DATA SOURCES

Seven databases (PubMed, Embase, Cochrane Library, Chinese National Knowledge Infrastructure, VIP Database, Wan-Fang Database, and Chinese Biomedical Database) were searched from inception to August 2024.

STUDY SELECTION

Two reviewers independently performed the literature selection. The included studies were randomized controlled trials providing peripheral electrical stimulation for patients with stroke.

DATA EXTRACTION

Two reviewers independently extracted data following a predeveloped Excel data collection sheet, including trial characteristics, intervention and comparator details, and outcome data. The risk of bias was evaluated by RoB2 tool, and the PRISMA guidelines were followed for reporting.

DATA SYNTHESIS

A total of 106 trials with 7513 participants were included. Meta-analysis showed that neuromuscular electrical stimulation (NMES) could be the optimal electrical stimulation protocol for improving the Fugl-Meyer Assessment score (standardized mean difference=1.67; 95% confidence interval [1.14-2.21]) and the modified Barthel Index score (standardized mean difference=1.73; 95% confidence interval [1.10-2.37]). The results showed that different frequencies of electrical stimulation ranked the top 5 in descending order for improving: (1) the Fugl-Meyer Assessment scores as follows: 20-30 Hz_NMES (surface under the cumulative ranking curve [SUCRA]=87.5%)>100 Hz_NMES (SUCRA=75.4%)>100 Hz_functional electrical stimulation (SUCRA=70.9%)>20/35 Hz_transcutaneous electrical acupoint stimulation (SUCRA=69.8%)>1-4 Hz_electrical acupuncture (SUCRA=69.6%) and (2) the modified Barthel Index scores as follows: 100 Hz_transcutaneous electrical nerve stimulation (SUCRA=77.3%)>5/15 Hz_NMES (SUCRA=68.3%)>100 Hz_transcutaneous electrical acupoint stimulation (SUCRA=65.6%)>35-50 Hz_functional electrical stimulation (SUCRA=64.8%)>1-4 Hz_electrical acupuncture (SUCRA=60.0%).

CONCLUSIONS

Adding electrical stimulation based on routine rehabilitation training can improve the motor dysfunction and activities of daily living of patients with stroke. Specifically, NMES with 20-30 Hz improves motor function best, whereas 100 Hz_transcutaneous electrical nerve stimulation improves activities of daily living best.

Peripheral Nerve Stimulation for Neuropathic Pain Management: A Narrative Review

This narrative review examines the therapeutic efficacy of peripheral nerve stimulation (PNS) in the treatment of neuropathic pain (NP), a type of pain arising from lesions or diseases of the somatosensory system with a global prevalence ranging from 6.90% to 10.00%. Traditional pharmacological interventions often fall short for many persons, highlighting the need for alternative treatments such as PNS, which has demonstrated significant promise with minimal side effects. The review summarizes the effectiveness of PNS in various NP conditions, including trigeminal neuralgia and postherpetic neuralgia, and underscores the need for further research to refine treatment approaches. The mechanism of PNS is discussed, involving the activation of non-nociceptive Aβ fibers and modulation of neurotransmitters, and offering pain relief through both peripheral and central pathways. Despite the proven efficacy of PNS, challenges remain, including the need for randomized controlled trials and the optimization of stimulation parameters. The review concludes that PNS is a promising treatment modality for NP, warranting additional high-quality trials to solidify its role in clinical practice.

Neural mechanisms of priming effects of spicy food pictures induced analgesia

In this study, the effects of the priming of spicy food pictures on pain perception were evaluated in female participants using standardized methods of pain. Results from behavior tests revealed that the priming of spicy food pictures significantly reduced pain perception, particularly at high-pain intensities. Electrophysiological analysis showed that the analgesic effects of spicy food pictures were linked to decreased pain-related event-related potentials, such as N2 and P2 amplitudes, and suppressed θ-oscillations in the sensorimotor cortex. Both N2 amplitudes and θ-oscillations activities were found to be correlated with participants' pain perception. These results suggest that spicy-arousal stimuli may act as an "antagonist" to the increase in N2 amplitudes and θ-oscillations power induced by pain and influence the neuronal networks involved in integrating spontaneous nociceptive resources, which supports the dissociation theory of pain sensation and affection. These findings highlight the potential use of spicy-arousal stimuli as an analgesic and emphasize the importance of considering both the intensity of the stimuli and the individual's emotional state in the assessment and treatment of pain.

Intensity-dependent modulation of cortical somatosensory processing during external, low-frequency peripheral nerve stimulation in humans

External low-frequency peripheral nerve stimulation (LFS) has been proposed as a novel method for neuropathic pain relief. Previous studies have reported that LFS elicits long-term depression-like effects on human pain perception when delivered at noxious intensities, whereas lower intensities are ineffective. To shed light on cortical regions mediating the effects of LFS, we investigated changes in somatosensory-evoked potentials (SEPs) during four LFS intensities. LFS was applied to the radial nerve (600 pulses, 1 Hz) of 24 healthy participants at perception (1 times), low (5 times), medium (10 times), and high intensities (15 times detection threshold). SEPs were recorded during LFS, and averaged SEPs in 10 consecutive 1-min epochs of LFS were analyzed using source dipole modeling. Changes in resting electroencephalography (EEG) were investigated after each LFS block. Source activity in the midcingulate cortex (MCC) decreased linearly during LFS, with greater attenuation at stronger LFS intensities, and in the ipsilateral operculo-insular cortex during the two lowest LFS stimulus intensities. Increased LFS intensities resulted in greater augmentation of contralateral primary sensorimotor cortex (SI/MI) activity. Stronger LFS intensities were followed by increased α (alpha, 9-11 Hz) band power in SI/MI and decreased θ (theta, 3-5 Hz) band power in MCC. Intensity-dependent attenuation of MCC activity with LFS is consistent with a state of long-term depression. Sustained increases in contralateral SI/MI activity suggests that effects of LFS on somatosensory processing may also be dependent on satiation of SI/MI. Further research could clarify if the activation of SI/MI during LFS competes with nociceptive processing in neuropathic pain.NEW & NOTEWORTHY Somatosensory-evoked potentials during low-frequency stimulation of peripheral nerves were examined at graded stimulus intensities. Low-frequency stimulation was associated with decreased responsiveness in the midcingulate cortex and increased responsiveness in primary sensorimotor cortex. Greater intensities were associated with increased midcingulate cortex θ band power and decreased sensorimotor cortex α band power. Results further previous evidence of an inhibition of somatosensory processing during and after low-frequency stimulation and point toward a potential augmentation of activity in somatosensory processing regions.