A systematic review of preclinical and clinical transcranial ultrasound neuromodulation and opportunities for functional connectomics

Bioadhesive hydrogel-coupled and miniaturized ultrasound transducer system for long-term, wearable neuromodulation

Transcranial focused ultrasound is a promising non-invasive method for neuromodulation, particularly for neurodegenerative and psychiatric conditions. However, its use in wearable systems has been limited due to bulky devices and reliance on ultrasound gel, which dehydrates and lacks stable adhesion for long-term use. Here, we present a miniaturized wearable ultrasound device, comparable in size to standard electrophysiological electrodes, integrated with a bioadhesive hydrogel for stable, long-term somatosensory cortical stimulation. Our air-cavity Fresnel lens based self-focusing acoustic transducer was fabricated via a lithography-free microfabrication process, achieving 30.7 W/cm² (1.92 MPa) acoustic intensity and 10 mm focal depth. The hydrogel couplant exhibited less than 13% acoustic attenuation and maintained a stable adhesion force of 0.961 N/cm for 35 days. Using this system, we successfully suppressed somatosensory evoked potentials elicited by functional electrical stimulation over 28 days, demonstrating the device's potential for long-term, wearable neuromodulation applications.

Transcranial ultrasound stimulation in neuromodulation: a bibliometric analysis from 2004 to 2024

Background

Transcranial ultrasound stimulation (TUS) is a non-invasive neuromodulation technique with promising clinical potential. Its therapeutic efficacy and safety are significantly influenced by stimulation parameters. However, the global research hotspots and future research trends of TUS application in the field of rehabilitation are unclear. This study analyzes the status of TUS research. Understand the annual publication trends, international and institutional cooperation pattern and influential authors and journals and keyword hotspot.

Methods

A comprehensive literature search was conducted on the Web of Science core database using TUS-related subject headings until 27 December 2024. Two researchers independently screened articles based on pre-determined inclusion and exclusion criteria. Software packages such as CiteSpace and VOSviewer were used to visualize the results.

Results

A total of 577 literatures were included. The results show that the annual publication volume shows an increasing trend, reaching a peak in 2024. The United States, China and Germany dominated the number of publications, with the largest number of institutions being Harvard University, the University of Toronto and Brigham and Women's Hospital. Brain stimulation is the journal with the most articles and citations. Research hotspots include transcranial magnetic stimulation, noninvasive brain stimulation, Parkinson's disease, and Alzheimer's disease.

Conclusion

A bibliometric analysis of the literature shows that research interest in transcranial ultrasound stimulation is growing rapidly, with annual publications growing exponentially since 2013 and receiving increasing attention from researchers. The findings suggest that TUS is currently used primarily in neurological diseases, particularly in the study of Parkinson's disease and Alzheimer's disease. At the same time, it is found that an emerging international cooperation model with the partnership between the United States, China and Germany as the core has gradually taken shape. Although preclinical studies have shown promising neuromodulator effects, the current study suggests that TUS needs to undergo further multicenter clinical validation. These findings provide evidence to guide future research priorities for non-invasive neuromodulation.

Investigating low intensity focused ultrasound pulsation in anhedonic depression-A randomized controlled trial

Introduction

Anhedonic depression is a subtype of depression characterized by deficits in reward processing. This subtype of depression is associated with higher suicide risk and longer depressive episodes, underscoring the importance of effective treatments. Anhedonia has also been found to correlate with alterations in activity in several subcortical regions, including the caudate head and nucleus accumbens. Low intensity focused ultrasound pulsation (LIFUP) is an emerging technology that enables non-invasive stimulation of these subcortical regions, which were previously only accessible with surgically-implanted electrodes.

Methods

This double-blinded, sham-controlled study aims to investigate the effects of LIFUP to the left caudate head and right nucleus accumbens in participants with anhedonic depression. Participants in this protocol will undergo three sessions of LIFUP over the span of 5-9 days. To investigate LIFUP-related changes, this 7-week protocol collects continuous digital phenotyping data, an array of self-report measures of depression, anhedonia, and other psychopathology, and magnetic resonance imaging (MRI) before and after the LIFUP intervention. Primary self-report outcome measures include Ecological Momentary Assessment, the Positive Valence Systems Scale, and the Patient Health Questionnaire. Primary imaging measures include magnetic resonance spectroscopy and functional MRI during reward-based tasks and at rest. Digital phenotyping data is collected with an Apple Watch and participants' personal iPhones throughout the study, and includes information about sleep, heart rate, and physical activity.

Discussion

This study is the first to investigate the effects of LIFUP to the caudate head or nucleus accumbens in depressed subjects. Furthermore, the data collected for this protocol covers a wide array of potentially affected modalities. As a result, this protocol will help to elucidate potential impacts of LIFUP in individuals with anhedonic depression.

Mechanistic insights into the neuroprotective effects of low-intensity transcranial ultrasound stimulation in post-cardiac arrest brain injury: Modulation of the Piezo1-Dkk3/PI3K-Akt pathway

Post-cardiac arrest brain injury (PCABI) remains a significant challenge, marked by high mortality and disability rates due to persistent neuroinflammation. This study explored the neuroprotective potential of low-intensity transcranial ultrasound stimulation (LITUS) in mitigating brain damage after cardiopulmonary resuscitation (CPR) using a murine model and in vitro assays. LITUS treatment improved 24-h survival rates and neurological recovery in cardiac arrest (CA) mice, as evidenced by behavioral assessments and reduced neurological deficit scores. Proteomic analyses revealed modulation of Piezo1-Dkk3/PI3K-Akt signaling pathway, characterized by decreased pro-inflammatory cytokines (IL-1β, IL-6, TNF-α). Mechanistic studies demonstrated that LITUS enhanced Piezo1 and Dkk3 activation, promoting calcium influx and anti-inflammatory responses. The Piezo1 antagonist GsMTx4 abrogated these effects, underscoring Piezo1's specific role. Additionally, in vitro experiments using oxygen/glucose deprivation and reoxygenation (OGD/R)-treated BV2 microglial cells confirmed that LITUS reduced inflammatory responses and enhanced cellular recovery via the Piezo1-Dkk3 axis. These findings highlight LITUS as a promising non-invasive therapeutic strategy to ameliorate PCABI by modulating neuroinflammation through the Piezo1-Dkk3/PI3K-Akt pathway. This work provides a basis for translational research and potential clinical applications in improving outcomes for CPR survivors.

A retrospective analysis of ultrasound neuromodulation therapy using transcranial pulse stimulation in 58 dementia patients

BACKGROUND

Novel ultrasound neuromodulation techniques allow therapeutic brain stimulation with unmet precision and non-invasive targeting of deep brain areas. Transcranial pulse stimulation (TPS), a multifrequency sonication technique, is approved for the clinical treatment of Alzheimer's disease (AD). Here, we present the largest real-world retrospective analysis of ultrasound neuromodulation therapy in dementia (AD, vascular, mixed) and mild cognitive impairment (MCI).

METHODS

The consecutive sample involved 58 patients already receiving state-of-the-art treatment in an open-label, uncontrolled, retrospective study. TPS therapy typically comprises 10 sessions (range 8-12) with individualized MRI-based target areas defined according to brain pathology and individual pathophysiology. We compared the CERAD-Plus neuropsychological test battery results before and after treatment, with the CERAD Corrected Total Score ( CTS) as the primary outcome. Furthermore, we analyzed side effects reported by patients during the treatment period.

RESULTS

CERAD Corrected Total Score (CTS) significantly improved (p = .017, d = .32) after treatment (Baseline: M = 56.56, SD = 18.56; Post-treatment: M = 58.65, SD = 19.44). The group of top-responders (top quartile) improved even by 9.8 points. Fewer than one-third of all patients reported any sensation during treatment. Fatigue and transient headaches were the most common, with no severe adverse events.

CONCLUSIONS

The findings implicate TPS as a novel and safe add-on therapy for patients with dementia or MCI with the potential to further improve current state-of-the-art treatment results. Despite the individual benefits, further randomized, sham-controlled, longitudinal clinical trials are needed to differentiate the effects of verum and placebo.

A practical guide to transcranial ultrasonic stimulation from the IFCN-endorsed ITRUSST consortium

Low-intensity Transcranial Ultrasonic Stimulation (TUS) is a non-invasive brain stimulation technique enabling cortical and deep brain targeting with unprecedented spatial accuracy. Given the high rate of adoption by new users with varying levels of expertise and interdisciplinary backgrounds, practical guidelines are needed to ensure state-of-the-art TUS application and reproducible outcomes. Therefore, the International Transcranial Ultrasonic Stimulation Safety and Standards (ITRUSST) consortium has formed a subcommittee, endorsed by the International Federation of Clinical Neurophysiology (IFCN), to develop recommendations for best practices in human TUS applications. The practical guide presented here provides a brief introduction into ultrasound physics and sonication parameters. It explains the requirements of TUS lab equipment and transducer selection and discusses experimental design and procedures alongside potential confounds and control conditions. Finally, the guide elaborates on essential steps of application planning for stimulation safety and efficacy, as well as considerations when combining TUS with neuroimaging, electrophysiology, or other brain stimulation techniques. We hope that this practical guide to TUS will assist both novice and experienced users in planning and conducting high-quality studies and provide a solid foundation for further advancements in this promising field.

Ultrasound Neuromodulation With Transcranial Pulse Stimulation in Alzheimer Disease: A Randomized Clinical Trial

Importance

Given the increasing prevalence of dementia and the limited treatment options available, ultrasound neuromodulation could serve as a novel add-on therapy to standard treatments for Alzheimer disease (AD). As ultrasound neuromodulation is still in its early stages, further research is essential to fully explore its potential in treating brain disorders.

Objective

To evaluate clinical and functional imaging effects of transcranial pulse stimulation (TPS) in patients with AD.

Design, Setting, and Participants

A randomized, double-blind, sham-controlled, crossover clinical trial was conducted at the Medical University of Vienna between January 1, 2017, and July 27, 2022. Sixty patients with clinically diagnosed AD receiving state-of-the-art treatment were randomly allocated to treatment sequence groups verum-sham (first cycle verum, second cycle sham, n = 30) and sham-verum (n = 30). Data analysis was performed from July 28, 2022, to September 5, 2024.

Intervention

Each participant received 6 verum and 6 sham TPS sessions (6000 pulses, 0.20 mJ/mm2, 5 Hz) to frontoparietal brain areas.

Main Outcomes and Measures

Neuropsychological tests, including the primary outcome Consortium to Establish a Registry for Alzheimer's Disease (CERAD) corrected total score (CTS), were performed at baseline and 1 week, 1 month, and 3 months following the stimulations in each cycle. Primary and secondary outcomes, including functional magnetic resonance imaging and Beck Depression Inventory-II, were analyzed by intention-to-treat analysis and, for sensitivity, by per protocol analysis.

Results

For the intention-to-treat analysis, 60 patients between ages 51 and 82 years (mean [SD], 70.65 [8.16] years; 30 females; 30 males) were included. The CERAD CTS increased by a mean (SD) of 2.22 (6.87) points in the verum condition from 70.93 (14.27) points at baseline to 73.15 (14.90) 3 months after stimulation, while the mean (SD) score in the sham condition increased by 1.00 (6.82) point vs baseline from 71.68 (13.62] at baseline to 72.68 (14.48) 3 months after stimulation. Primary data analysis of the condition × session interaction was not significant (P = .68; partial η2 [ηp2] = 0.01), but its interaction with age was P = .003; ηp2 = 0.08, followed by post hoc analyses of age subsamples. Although several patients older than 70 years benefited from verum TPS, only the younger subgroup (≤70 years) showed significantly higher CTS increases for verum in all poststimulation sessions (condition × session: P = .005; ηp2 = 0.16). At 3 months after stimulation, for example, a mean (SD) 3.91 (7.86)-point increase was found for verum TPS in the younger patients, but a mean (SD) CTS decrease of 1.83 (5.80) was observed for sham. Memory-associated brain activation was significantly higher after verum TPS in the precuneus, visual, and frontal areas, while resting state functional connectivity was significantly upregulated in the dorsal attention network. In the per protocol sample, a significant reduction of the Beck Depression Inventory-II scores 3 months following verum TPS was found (verum baseline: 7.27 [5.87]; verum 3 months after stimulation: 5.27 [5.27]; sham baseline: 6.70 [5.65]; sham 3 months after stimulation: 6.22 [4.40]; P = .008; ηp2 = 0.23). During both verum and sham conditions, the most common observed adverse symptom was depression; no major neuropathologic change was detected in the patients by detailed neuroradiologic assessments.

Conclusions and Relevance

In this randomized clinical trial of TPS in patients with AD, a 2-week verum treatment improved cognitive scores in the younger subgroup, ameliorated depressive symptoms, and induced upregulation of functional brain activation and connectivity. These findings suggest TPS may be a safe and promising add-on therapy for patients with AD receiving state-of-the-art treatment.

Trial Registration

ClinicalTrials.gov Identifier: NCT03770182.

Novel NIBS in psychiatry: Unveiling TUS and TI for research and treatment

Mental disorders pose a significant global burden and constitute a major cause of disability worldwide. Despite strides in treatment, a substantial number of patients do not respond adequately, underscoring the urgency for innovative approaches. Traditional non-invasive brain stimulation techniques show promise, yet grapple with challenges regarding efficacy and specificity. Variations in mechanistic understanding and reliability among non-invasive brain stimulation methods are common, with limited spatial precision and physical constraints hindering the ability to target subcortical areas often implicated in the disease aetiology. Novel techniques such as transcranial ultrasonic stimulation and temporal interference stimulation have gained notable momentum in recent years, possibly addressing these shortcomings. Transcranial ultrasonic stimulation (TUS) offers exceptional spatial precision and deeper penetration compared with conventional electrical and magnetic stimulation techniques. Studies targeting a diverse array of brain regions have shown its potential to affect neuronal excitability, functional connectivity and symptoms of psychiatric disorders such as major depressive disorder. Nevertheless, challenges such as target planning and addressing acoustic interactions with the skull must be tackled for its widespread adoption in research and potentially clinical settings. Similar to transcranial ultrasonic stimulation, temporal interference (TI) stimulation offers the potential to target deeper subcortical areas compared with traditional non-invasive brain stimulation, albeit requiring a comparatively higher current for equivalent neural effects. Promising yet still sparse research highlights TI's potential to selectively modulate neuronal activity, showing potential for its utility in psychiatry. Overall, recent strides in non-invasive brain stimulation methods like transcranial ultrasonic stimulation and temporal interference stimulation not only open new research avenues but also hold potential as effective treatments in psychiatry. However, realising their full potential necessitates addressing practical challenges and optimising their application effectively.

Transcranial Focused Ultrasound Neuromodulation in Psychiatry: Main Characteristics, Current Evidence, and Future Directions

Non-invasive brain stimulation (NIBS) techniques are designed to precisely and selectively target specific brain regions, thus enabling focused modulation of neural activity. Among NIBS technologies, low-intensity transcranial focused ultrasound (tFUS) has emerged as a promising new modality. The application of tFUS can safely and non-invasively stimulate deep brain structures with millimetric precision, offering distinct advantages in terms of accessibility to non-cortical regions over other NIBS methods. However, to date, several tFUS aspects still need to be characterized; furthermore, there are only a handful of studies that have utilized tFUS in psychiatric populations. This narrative review provides an up-to-date overview of key aspects of this NIBS technique, including the main components of a tFUS system, the neuronavigational tools used to precisely target deep brain regions, the simulations utilized to optimize the stimulation parameters and delivery of tFUS, and the experimental protocols employed to evaluate the efficacy of tFUS in psychiatric disorders. The main findings from studies in psychiatric populations are presented and discussed, and future directions are highlighted.

The future of transcranial ultrasound as a precision brain interface

Our understanding of brain circuit operations and disorders has rapidly outpaced our ability to intervene and restore them. Developing technologies that can precisely interface with any brain region and circuit may combine diagnostics with therapeutic intervention, expediting personalised brain medicine. Transcranial ultrasound stimulation (TUS) is a promising noninvasive solution to this challenge, offering focal precision and scalability. By exploiting the biomechanics of pressure waves on brain tissue, TUS enables multi-site targeted neuromodulation across distributed circuits in the cortex and deeper areas alike. In this Essay, we explore the emergent evidence that TUS can functionally test and modify dysfunctional regions, effectively serving as a search and rescue tool for the brain. We define the challenges and opportunities faced by TUS as it moves towards greater target precision and integration with advanced brain monitoring and interventional technology. Finally, we propose a roadmap for the evolution of TUS as it progresses from a research tool to a clinically validated therapeutic for brain disorders.

Clinical recommendations for non-invasive ultrasound neuromodulation

Non-invasive ultrasound neuromodulation has experienced exponential growth in the neuroscientific literature, recently also including clinical studies and applications. However, clinical recommendations for the secure and effective application of ultrasound neuromodulation in pathological brains are currently lacking. Here, clinical experts with neuroscientific expertise in clinical brain stimulation and ultrasound neuromodulation present initial clinical recommendations for ultrasound neuromodulation with relevance for all ultrasound neuromodulation techniques. The recommendations start with methodological safety issues focusing on technical issues to avoid harm to the brain. This is followed by clinical safety issues focusing on important factors concerning pathological situations.