Modelling and Preliminary Clinical Validation of Home-based Menstrual Neuromodulation Therapy

demonstrated a clinically meaningful decline in menstrual pain symptoms in the active group, with medium effect sizes for both pain reduction (Cohen’s d=0.53) a nd functionality (Cohen’s d=0.47) , based on Nettle™’s protocol focused on the electric field within the medial prefrontal cortex .

include the use of generalised brain models and small sample size, highlighting the need for further research with comprehensive modelling and larger clinical trials to validate and understand the effects of Nettle™ as a menstrual neuromodulation therapy. Clinical Relevance — This study underscores Nettle™’s potential as a non -invasive, cost-efficient intervention for PD, with implications for broader applications in women’s health. Keywords—non-invasive brain stimulation, tDCS, women’s health, dysmenorrhea, PMS, menstrual neuromodulation therapy I. INTRODUCTION Dysmenorrhea, defined as chronic, recurring pelvic pain during menstruation, manifests predominantly as primary dysmenorrhea (PD) or less commonly as secondary dysmenorrhea. PD, a prevalent gynaecological disorder absent of other pathology, induces pain preceding and during menses. It is often accompanied by psychological symptoms —such as anxiety and depression—along with physiological effects like nausea, migraines, and diarrh oea. The collecti on of these symptoms is referred to as premenstrual syndrome (PMS). An estimated 17-90% of women of reproductive age experience menstrual symptoms, which remain an inadequately addressed gynaecologic issue [1]. These symptoms can significantly impact daily functioning and quality of life, particularly at the onset of the menstrual period, affecting educational and occupational activities. PD is linked to alteratio ns in brain metabolism and functional connectivity in regions implicated in pain modulation, including the primary motor cortex (M1), medial prefrontal cortex (mPFC), posterior cingulate cortex, and the insula, which exhibit abnormal functional patterns [2]. These areas contribute to the emotional and affective regulation of pain, cognitive control, and pain generali sation. Women with PD demonstrate heightened theta wave (4 -7 Hz) activity in these pain-associated cerebral regions [3]. Similarly, women with severe p remenstrual symptoms demonstrate alpha (8-12 Hz) wave asymmetry in the prefrontal regions of the brain [4]. The interrelation of pain with depressive and anxious states may be crucial for elucidating the role of theta and alpha activity in the sensory -emotional pain processing specific to PD. Crucially, these neurocognitive alterations are not confined to menstrual episodes, suggesting PD should be understood as a chronic pain condition [5]. This understanding of the enduring neurocognitive and behavioural changes in women with PD paves the way for novel, non -pharmacological treatment approaches that are cost-effective and have minimal side effects. Non-invasive brain stimulation (NIBS) has been used in several clinical conditions aiming to improve motor, cognitive, affective-behavioural and physical function . The clinical application of NIBS has been gaining prominence in new consensuses and guidelines in physical and cognitive rehabilitation aimed to improve or restore function in chronic diseases. Transcranial direct current stimulation (tDCS) is The clinical validation work was supported by the funding of Prof Rodrigo Pegado and Prof Maria Thereza Micussi at the Federal University of Rio Grande do Norte. The modelling work was supported by grant funding to Samphire Neuroscience Ltd from UK Research & Innovation. All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The copyright holder for thisthis version posted February 4, 2024. ; https://doi.org/10.1101/2024.02.02.24302224doi: medRxiv preprint NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice. particularly noted for its scalability and involves administering a constant low-intensity microcurrent of 1 to 4 mA to the scalp. This results in modulated cortical excitability, contingent on specific parameters such as duration, intensity, and electrode placement, which contribute to its therapeutic effects. Several investigations have been published, ranging from computational simulations to animal experiments and human clinical trials, support ing the use of tDCS as an effective, non -invasive, and cost -efficient intervention with minimal side effects for disorders such as major depre ssive disorder, fibromyalgia, and stroke rehabilitation, among others [6]. In particular, studies examining tDCS in women with PD have reported beneficial outcomes for pain management [7], functionality and anxiety [8]. Importantly, the efficacy of tDCS is significantly influenced by the configuration of electrode placement. Anodic stimulation at the primary motor cortex (M1), using a C3/Fp2 montage as per the 10/20 EEG system, enhances pain modulation, while similar stimulation at the dorsolateral prefrontal cortex (DLPFC), using an F3/Fp2 montage, has been associated with reduced anxiety. tDCS is typically prescribed by physicians or physiotherapists, varying with national regula tions, and administered under professional supervision in clinical settings. The push for remote rehabilitation, including tDCS, represents a significant shift in patient care, a trend accelerated by the COVID-19 pandemic's social distancing measures. While in - person treatment at research facilities or clini cs is effective, it presents logistical challenges, requiring patient s to commit to numerous sessions. This commitment often incurs considerable costs for transportation, ti me, and meals, and can lead to absence from work or school, limiting overall treatment accessibility. A remote tDCS model that is safe, user -friendly, and associated with low adverse effects could enhance adherence and provide an alternative therapy for wo men suffering from primary dysmenorrhea (PD) and PMS [9]. Existing remote tDCS prot ocols have targeted chro nic pain and various musculoskeletal and behavio ural disorders but have not specifically addressed women’s health concerns, including PD. Nettle™ by Samphire Neuroscience, a novel home -use tDCS device, has been developed to meet this need. It operates based on val idated stimulation parameters and electrode configurations to mitigate PD symptoms. Designed to resemble a women’s hair accessory for discretion, Nettle™ is a wireless, Bluetooth-enabled wearable device managed through the Samphire App. The app gu ides use rs through session setup, checks for contraindications, customi ses session parameters, and allows for session control, including starting, pausing, and stopping, as well as troubleshooting support and collection of post-session feedback. This is a modelling and clinical validation study with healthy volunteers aiming to evaluate the potential of the Nettle™ home-based tDCS system with a focus on women’s health. The specific aims of this study were to (1) understand the electric field patterns and strengths associated with the use of Nettle™, and (2) assess the immediate efficacy of Nettle™ in alle viating pain and mood symptoms associated with menstruation. II. METHODS A. Electric Field Modelling & Simulations Head models for tDCS simulations were created using the finite element method (FEM) with a realistic head model mesh derived from an example subject’s structural magnetic resonance scans in SimNIBS [10]. Default tissue conductivities were used (bone (0.010 S/m) , scalp (0.465 S/m), grey matter (0.275 S/m), white matter (0.126 S/m), cerebrospinal fluid (1.654 S/m)). Simulation results were visualised with Gmsh and MATLAB, and all calculations were conducted in MATLAB. Active electrode montages were determined by simulating electrodes on a 10 -20 EEG cap that represents the potential positions of electrodes on the scalp and compiles a matrix of the electric fields generated by every electrode while keeping the return electrode constant, then optimised to reach a particular field strength at the target. DLPFC MNI coordinates were (-49.33; 52.25; 73.03), and M1 coordinates were (-64.32, -15.38, 82.66) all in millimetres. For tDCS modelling, rectangular 5.0 cm x 2.0 cm sponge electrodes were used with a 2.5 mm thickness. The specific positions in the 10 -20 electrode system for each of the montages are shown in Figure 1. B. Preliminary Clinical Validation Trial Design The clinical validation study was a single-centre triple- blinded study conducted at the Federal University of Rio Grande do Norte (UFRN) in Natal, Brazil. The study was previously approved by the Research Ethics Committee of UFRN under number 5.508.364. Inclusion criteria admitted participants, who: (1) were 18-45 years old, (2) had a regular menstrual cycle, (3) were not lactating, (4) had no history of brain surgery, tumours, or intracranial metal implantation, and (5) had no history of chronic genitourinary infections, alcohol, or drug abuse. Exclusion criteria were: (1) patients presenting with a history of dizziness or epileptic disease, (2) pregnancy, and (3) metal implants in the head. A total of 34 women participated in the study. Participants were enrolled by the blinded investigators and randomly allocated (1:1) to receive active tDCS (n = 18) or sham tDCS (n = 16). Stratified randomisation was done using the order of entry into the study to assign each participant to either the active or sh am group. An external blinded research assistant generated the allocation sequence. Participants and evaluators were blinded to group allocation throughout the trial. The study was run for a single intervention menstrual cycle in order to establish the clinical trend effects of the intervention. C. Menstrual Neuromodulation Therapy Intervention The study consisted of a single -day assessment and intervention with 4 stages: (1) initial meeting with the participants to introduce the project, complete informed consent procedures and baseline evaluation of me nstrual symptoms, (2) 5-day use of Nettle™ at-home by the participant in the 5 days of their late luteal phase , (3) intervention evaluation on the first day of their menstrual cycle following the use of Nettle™, (4) evaluation of menstrual symptoms one month following the use of Nettle™. All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The copyright holder for thisthis version posted February 4, 2024. ; https://doi.org/10.1101/2024.02.02.24302224doi: medRxiv preprint The Samphire App was configured in the participants’ native (Brazilian Portuguese) language to ensure accessibility, with an option to change it to English. Nettle™ was set to deliver direct current to the scalp at the M1 area of the brain (M1, anodal EEG 10 -20 C3/C4). The device has four sponge electrodes (1 0.25 cm2) that must be impregnated by the user with a saline (0.9% NaCl) solution before placing the device on the head. Each participant self - administered five 20-minute sessions, one daily, in their late luteal phase. In the active tDCS group, the current was ramped up from 0 to 2.0 mA over 30 seconds, held constant for 19 minutes, and ramped down over 30 seconds, for a total session time of 20 minutes. In the sham tDCS group, to ensure blinding, the current was ramped up to 2 mA over 30 seconds, then ramped down to 0.01 mA, considered negligible, and held at the negligible output for 19.5 minutes, for a total session duration of 20 minutes . This method produces the same mimic sensations such as itching, and tingling observed during active tDCS, enabling blinding to be achieved [9], as shown in a previous usability study . Both active and sham tDCS groups used identical devices, with the session type being determined by a previously randomised code input into the Samphire App. During tDCS use, participants were instructed to feel free and continue with their normal routine. D. Outcome measures Primary outcomes were changes in pain scores on a visual analog scale and the 6 -minute walking test assessing participant functionality. Secondary measures included a range of tests to assess mental health impacts, such as low mood , anxiety, and negative and positive emotionality , which are beyond the scope of this paper. E. Statistical analysis SPSS software version 19.0 (IBM Corp., Armonk, NY, USA) was used for statistical analyses. Clinical and sociodemographic characteristics were described by means and standard deviations or by frequency tables for qualitative parameters. A chi -squared test was used to compare the distributions of qualitative variables. The Shapiro-Wilk test was used to assess the normality of the distribution. To compare data between groups, an unpaired t -test or Mann- Whitney were used. Statistical significance was set at p < 0.05. III. RESULTS & DISCUSSION A. Electrical Field Modelling Electric field modelling results suggested that under Nettle™’s stimulation protocol, t he majority of the electr ic field strength is concentrate d in the mPFC, with secondary locations in the DLPFC and motor cortices) (Figure 1). Recent evidence suggested strong connections between the mPFC and the posterior cingulate and insula [11], which may explain why even after a single cycle use, users could expect to experience clinically significant results. Fig. 1. Anterior, dorsal and sagittal views of electric field modelli ng results for th e Nettle™ device. Electric field modelling result s suggest that under Nettle™’s stimulation protocol, the maj ority of the electric field strength (measured in V /m units, max at 0.7 2 V/m) is concentrated in the dorsolateral and medial prefrontal cortices, a s well as the motor cortex. It also shows that there is negligible direct penetration o f the electrical stimulation into subcortical areas of the brain. Electrode currents are measured in A. B. Effect on pain perception within a single cycle In line with observations from the NIBS literature [12], there was a large initial sham and active effect from baseline to the intervention menstrual cycle, associated with the novelty of treatment. However, according to the predictions around the longer-term neuroplasticity effects of NIBS on pain perception [13], symptoms rebounded in the sham group in the follow-up menstrual cycle, while continuing to be suppressed in the active group (average pain severit y decrease of -52.8% in the active group vs -24.43% decrease in the sham group ). There was a medium effect siz e ( Cohen’s d=0.53) (Figure 2). This change suggests a cl inically meaningful decline in menstrual pain symptoms in the active group after a single cycle of use. Fig. 2. Pain Visual Analog Scale measure for active and sham groups. A significant difference was found between T0 and T2 (p = 0.002, d = 0.53 (CI - 1.215; 0.155 ) for the acti ve, but not the sham group. *Denotes significant intragroup difference. C. Effect on functionality within a single cycle There were tempor ary increases in functionality, or physical performance, in the active but not the sham group after a single cycle of use, with a medium effect size (Cohen’s d=0.47) (Figure 3). T0 T1 T2 0 10 20 30 40 50 60 70 80 90 100 Sham Acti ve * VAS All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The copyright holder for thisthis version posted February 4, 2024. ; https://doi.org/10.1101/2024.02.02.24302224doi: medRxiv preprint This is expected, as physical effects are usually considered to be a short - rather than longer -term effect o f NIBS underlying this menstrual neuromodulation therapy. Fig. 3. Six-minute walking test (6MWT) functionality measure for active and sham groups. A significant difference was found between T0 and T1 (p = 0.04, d = 0.47 (CI -0.20; 1.15)) for the active, but not the sham group. IV. LIMITATIONS & CONCLUSION This paper presents a brief overview of the reasoning, modelling, and preliminary clinical and public health implications of a new device, Nettle™, able to deliver non- invasive menstrual neuromodulation therapy , with two core limitations. Firstly, the brain models used in this study are not derived from a s pecific participant in the study but are rather a simplified representation of the brain morphology and tissue behaviour based on population data. This type of electric field modelling does not account for the temporal dimension of the electric field magnitude or the spatial dimension and morphology of individual neuro ns. A multi-compartmental neuronal model, able to accou nt for the orientation of electric field vectors, the activating function and network dynamics would all result in a more accurate model of the amplitudes and dispersion of electrical fields in a specific user. Secondly, this was a preliminary clinical study, the purpose of which was to validate the clinical premise of using NIBS in the management of long -term, chronic conditions disproportionately impacting the quality of li fe of women. Thereby, it is likely to have been underpowered from a sample size and a duration perspective to be able to draw more conclusive results on the effect, variability and effect size of the clinical efficacy of the Nettle™ device. Further studies are set to explore more complex modelling and simulations of the underlying biophysical effects of Nettle™ on individual neuronal and net work connectivity, as well as larger clinical samples for more conclusive results. Overall, this paper demonstrates that NIBS could be an effective modality for the management of long-term conditions in the area of women ’s health, especially for menstrual symptoms, such as premenstrual syndrome and menstrual pain.

[1] Yonkers, K. A., O’Brien, P. M. S., & Eriksson, E. (2008). Premenstrual syndrome. Lancet, 371(9619), 1200 –1210. https://doi.org/10.1016/S0140-6736(08)60527-9 [2] Wu, T. -H., Tu, C. -H., Chao, H. -T., Li, W. -C., Low, I., Chuang, C. -Y., Yeh, T. -C., Cheng, C. -M., Chou, C. -C., Chen, L. -F., & Hsieh, J. -C. (2016). Dynamic Changes of Functional Pain Connectome in Women with Primary Dysmenorrhea. Scientific Reports , 6, 24543. https://doi.org/10.1038/srep24543 [3] Lee, P.-S., Low, I., Chen, Y. -S., Tu, C. -H., Chao, H. -T., Hsieh, J. -C., & Chen, L. -F. (2017). Encoding of menstrual pain experience with theta oscillations in women with pr imary dysmenorrhea. Scientific Reports, 7, 15977. https://doi.org/10.1038/s41598-017-16039-4 [4] Lin, I.-M., Tsai, Y.-C., Peper, E., & Yen, C.-F. (2013). Depressive mood and frontal alpha asymmetry during the luteal phase in premenstrual dysphoric disorder. The Journal of Obstetrics and Gynaecology Research, 39(5), 998–1006. https://doi.org/10.1111/jog.12020 [5] Gui, S. -G., Chen, R. -B., Zhong, Y. -L., & Huang, X. (2021). Machine Learning Analysis Reveals Abnormal Static and Dynamic Low - Frequency Oscillations Indicative of Long -Term Menstrual Pain in Primary Dysmenorrhea Patients. Journal of Pain Research , 14, 3377 – 3386. https://doi.org/10.2147/JPR.S332224 [6] Fregni, F., El -Hagrassy, M. M., Pacheco -Barrios, K., Carvalho, S., Leite, J., Simis, M., Brunelin, J., Nakamura -Palacios, E. M., Marangolo, P., Venkatasubramanian, G., San -Juan, D., Caumo, W., Bikson, M., Brunoni, A. R., & Neuromodulation Center Working Group. (2021). Evidence-Based Guidelines and Secondary Meta -Analysis for the Use of Transcranial Direct Current Stimulation in Neurological and Psychiatric Disorders. International Journal of Neuropsychopharmacology , 24(4), 256–313. https://doi.org/10.1093/ijnp/pyaa051 [7] Pegado, R., Silva, L. K., da Silva Dantas, H., Andrade Câmara, H., Andrade Mescouto, K., Silva -Filho, E. M., Lopes, J. M., Micussi, M. T. A. B. C., & Correia, G. N. (2020). Effects of Transcranial Direct Current Stimulation for Treatment of Primary Dysmenorrhea: Preliminary

of a Randomized Sham -Controlled Trial. Pain Medicine (Malden, Mass.), 21(12), 3615–3623. https://doi.org/10.1093/pm/pnz202 [8] Dutra, L. R. D. V., Pegado, R., Silva, L. K., da Silva Dantas, H., Câmara, H. A., Silva -Filho, E. M., Correia, G. N., & Micussi, M. T. A. B. C. (2020). Modulating Anxiety and Functional Capacity with Anod al tDCS Over the Left Dorsolateral Prefrontal Cortex in Primary Dysmenorrhea. International Journal of Women’s Health , 12, 243–251. https://doi.org/10.2147/IJWH.S226501 [9] Radyte, E., Micussi, M. T., Cook, A. A., Alves, T., Bernatavicius, E., Rodrigues, Y., & Pegado, R. (2023). Development and testing of a novel IoT consumer tDCS device for the treatment of primary dysmenorrhea. Brain Stimulation: Basic, Translational, and Clinical Research in Neuromodulation, 16(1), 303. https://doi.org/10.1016/j.brs.2023.01.548 [10] Saturnino, G. B., Puonti, O., Nielsen, J. D., Antonenko, D., Madsen, K. H., & Thielscher, A. (2019). SimNIBS 2.1: A Comprehensive Pipeline for Individualized Electric Field Modelling for Transcranial Brain Stimulation. In S. Makarov, M. Horner, & G. Noetscher (Eds.), Brain and Human Body Modeling: Computational Human Modeling at EMBC 2018. Springer. http://www.ncbi.nlm.nih.gov/books/NBK549569/ [11] Bacon, E. J., Jin, C., He, D., Hu, S., Wang, L., Li, H., & Qi, S. (2023). Functional and effective connectivity analysis of drug -resistant epilepsy: A resting -state fMRI analysis. Frontiers in Neuroscience , 17. https://www.frontiersin.org/articles/10.3389/fnins.2023.1163111 [12] Vergallito, A., Gallucci, A., Pisoni, A., Punzi, M., Caselli, G., Ruggiero, G. M., Sassaroli, S., & Romero Lauro, L. J. (2021). Effectiveness of noninvasive brain stimulation in the treatment of anxiety disorders: A meta-analysis of sham or behaviour -controlled studies. Journal of Psychiatry & Neuroscience: JPN , 46(6), E592 –E614. https://doi.org/10.1503/jpn.210050 [13] Huang, Y. -Z., Lu, M. -K., Antal, A., Classen, J., Nitsche, M., Ziemann, U., Ridding, M., Hamada, M., Ugawa, Y., Jaberzadeh, S., Suppa, A., Paulus, W., & Rothwell, J. (2017). Plasticity induced by non-invasive transcranial brain stimulation: A position paper. Clinical Neurophysiology, 128(11), 2318–2329. https://doi.org/10.1016/j.clinph.2017.09.007 T0 T1 T2 200 250 300 350 400 450 500 550 600 Sham Acti ve 6MWT All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The copyright holder for thisthis version posted February 4, 2024. ; https://doi.org/10.1101/2024.02.02.24302224doi: medRxiv preprint