Mechanisms of theta burst transcranial ultrasound induced plasticity in the human motor cortex

Cortical Plasticity Induced by Pairing Primary Motor Cortex Transcranial Magnetic Stimulation With Subthalamic Nucleus Magneto-Acoustic Coupling Stimulation

Paired cortical and deep stimulation has the potential to induce enhanced cortical plasticity. Ideally, such stimulation should be noninvasive and precisely controlled. A novel paired stimulation method, combining transcranial magnetic stimulation (TMS) with transcranial magneto-acoustic coupled stimulation (TMAS), named TMS-TMAS, was proposed to achieve such stimulations. Although the primary motor cortex (M1) is stimulated using TMS, the pulsed magnetic field is coupled with a focused ultrasound field to achieve TMAS-based focused electrical stimulation of the subthalamic nucleus (STN) via the magneto-acoustic coupling effect. Cortical plasticity is induced by precisely controlling the timing of magnetic pulse and ultrasound emissions based on spike timing-dependent plasticity (STDP). The experimental system achieved cortical-focused magnetic stimulation with a transverse resolution of 4.3 mm, a longitudinal resolution of 2.8 mm, and a magnetic field intensity of 1.6 T in the M1 region. Additionally, deep-focused electrical stimulation with a transverse resolution of 1.6 mm, a longitudinal resolution of 9.9 mm, and a coupled electric field intensity of 280 mV/m in the STN region was realized. In vivo animal experiments demonstrated that TMS-TMAS enhanced the amplitude of motor evoked potential (MEP) and reduced response latency. Simulation and experimental results confirmed that TMS-TMAS achieves high spatial resolution, noninvasive paired stimulation of the cortex and deep nuclei, and induces enhanced cortical plasticity when the stimulation sequence satisfies the STDP criteria. This method provides a promising approach for noninvasive paired stimulation and is expected to advance brain science research and the rehabilitation of neuropsychiatric disorders involving deep brain structures.

Non-invasive brain stimulation to modulate neural activity in Parkinson's disease

Despite its potential to modulate brain and network activity, non-invasive brain stimulation is not yet clinically applied for treating Parkinson's disease. We here review recent findings that illustrate how various non-invasive stimulation techniques can modify pathological and compensatory activities. Due to unavoidable heterogeneities and low effect sizes of the reviewed studies, a deeper understanding of the mechanisms of action will be critical for refining clinical effectiveness and generating consistent results.

Individualized non-invasive deep brain stimulation of the basal ganglia using transcranial ultrasound stimulation

Transcranial ultrasound stimulation (TUS) offers precise, non-invasive neuromodulation, though its impact on human deep brain structures remains underexplored. Here we examined TUS-induced changes in the basal ganglia of 10 individuals with movement disorders (Parkinson's disease and dystonia) and 15 healthy participants. Local field potentials were recorded using deep brain stimulation (DBS) leads in the globus pallidus internus (GPi). Compared to sham, theta burst TUS (tbTUS) increased theta power during stimulation, while 10 Hz TUS enhanced beta power, with effects lasting up to 40 min. In healthy participants, a stop-signal task assessed tbTUS effects on the GPi, with pulvinar stimulation serving as an active sham. GPi TUS prolonged stop-signal reaction times, indicating impaired response inhibition, whereas pulvinar TUS had no effect. These findings provide direct electrophysiological evidence of TUS target engagement and specificity in deep brain structures, suggesting its potential as a noninvasive DBS strategy for neurological and psychiatric disorders.

A New Multi-Mode, High Pressure Portable Transcranial Ultrasound Stimulation System

OBJECTIVE

Transcranial ultrasound stimulation (TUS) is a promising non-invasive neuromodulation method for brain disorders. Commonly-used TUS systems in research include custom-built and commercial devices. Custom-built devices typically consist of traditional function generator, power amplifier, and ultrasound transducer. Due to cumbersome wiring and absence of dedicated control software, the operation of these devices is inconvenient. Commercial devices often have limited waveform modes and cannot perform ultrasound modulation with complex waveforms. These limitations limit the application of TUS technology by ordinary users. Therefore, we propose a portable TUS system with multiple modes and high acoustic pressure.

METHODS

The proposed portable TUS system utilizes a high-power multi-mode stimulator, and an ultrasound transducer with impedance matching module to achieve multiple modes and high acoustic pressure ultrasound neuromodulation.

RESULTS

The stimulator can output four types of waveforms: continuous pulse continuous stimulus (CPCS), intermittent pulse continuous stimulus (IPCS), continuous pulse intermittent stimulus (CPIS), and intermittent pulse intermittent stimulus (IPIS). When using a same transducer, it generates a peak negative pressure that is nearly identical to one produced by a commercial device. And compared to commercial transducer, the peak negative pressure of our transducer is significantly higher, reaching a maximum of 0.95 MPa.

CONCLUSION

In-vitro experiments were conducted using rat hippocampal brain slices. The experimental results demonstrated the effectiveness of the TUS system for neural stimulation.

SIGNIFICANCE

It offers a design method of a portable multi-mode, high pressure TUS system, which is used for complex neural modulation research.

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.

Neuromodulation with Ultrasound: Hypotheses on the Directionality of Effects and Community Resource

Low-intensity Transcranial Ultrasound Stimulation is a promising non-invasive technique for brain stimulation and focal neuromodulation. Research with humans and animal models has raised the possibility that TUS can be biased towards enhancing or suppressing neural function. Here, we first collate a set of hypotheses on the directionality of TUS effects and conduct an initial meta-analysis on the available healthy human participant TUS studies reporting stimulation parameters and outcomes (n = 47 studies, 52 experiments). In these initial exploratory analyses, we find that parameters such as the intensity and continuity of stimulation (duty cycle) with univariate tests show only statistical trends towards likely enhancement or suppressed of function with TUS. Multivariate machine learning analyses are currently limited by the small sample size. Given that human TUS sample sizes will continue to increase, predictability on the directionality of TUS effects could improve if this database can continue to grow as TUS studies more systematically explore the TUS stimulation parameter space and report outcomes. Therefore, we establish an inTUS database and resource for the systematic reporting of TUS parameters and outcomes to assist in greater precision in TUS use for brain stimulation and neuromodulation. The paper concludes with a selective review of human clinical TUS studies illustrating how hypotheses on the directionality of TUS effects could be developed for empirical testing in the intended clinical application, not limited to the examples provided.

Advancements and prospects of transcranial focused ultrasound in pain neuromodulation

ABSTRACT

Transcranial focused ultrasound (tFUS) is an emerging noninvasive neuromodulation technology that has shown great potential in pain modulation. This review systematically elucidates the multilevel biological mechanisms of tFUS neuromodulation, from network-wide effects to cellular and molecular processes, as well as broader systemic influences. Preliminary animal pain model studies have revealed tFUS's ability to improve pain behavioral indicators and modulate neural circuit activity under pathological conditions. A small number of clinical studies also suggest that tFUS may have certain benefits in improving symptom experience and emotional state in chronic pain patients. However, current research generally has limitations such as small sample sizes and short follow-up periods. More high-quality studies are needed to verify the long-term effects and safety of tFUS pain treatment. Overcoming these limitations and advancing large-scale clinical translational research will help fully exploit the application potential of tFUS in precision pain medicine and provide new treatment options for pain relief.

Reliable quantification of neural entrainment to rhythmic auditory stimulation: simulation and experimental validation

Objective.Entrainment has been considered as a potential mechanism underlying the facilitatory effect of rhythmic neural stimulation on neurorehabilitation. The inconsistent effects of brain stimulation on neurorehabilitation found in the literature may be caused by the variability in neural entrainment. To dissect the underlying mechanisms and optimize brain stimulation for improved effectiveness, it is critical to reliably assess the occurrence and the strength of neural entrainment. However, the factors influencing entrainment assessment are not yet fully understood. This study aims to investigate whether and how the relevant factors (i.e. data length, frequency bandwidth, signal-to-noise ratio (SNR), center frequency, and the constant component of stimulus-response phase-difference) influence the assessment reliability of neural entrainment.Approach.We simulated data for 28 scenarios to answer above questions. We also recorded experimental data to verify the findings from our simulation study.Main results.A minimal data length is required to achieve reliable neural entrainment assessment, and this requirement critically depends on the bandwidth and SNR, but is independent of the center frequency and the constant component of stimulus-response phase-difference. Furthermore, changing of bandwidth is accompanied by the change of SNR.Significance.The present study has revealed how data length, bandwidth, and SNR critically affect the assessment reliability of neural entrainment. The findings provide a foundation for the parameter setting in experiment design and data analysis in neural entrainment studies. While this study is within the context of rhythmic auditory stimulation, the conclusions may be applicable for neural entrainment to other rhythmic stimulations.

Effects of Low Intensity Focused Ultrasound Stimulation Combined With Functional Electrical Stimulation on Corticospinal Excitability and Upper Extremity Fine Motor Function

INTRODUCTION

Functional electrical stimulation (FES) is used to retrain motor function in neurological disorders but typically requires multiple sessions and shows limited benefits in chronic cases. Low-intensity transcranial focused ultrasound stimulation (TUS) is a noninvasive brain stimulation (NIBS) method offering greater focality and deeper penetration than current NIBS techniques. TUS delivered in a theta burst pattern (tbTUS) for 80 s produces neuroplastic changes with long-term potentiation-like effects lasting up to 60 min in healthy adults. Since tbTUS increases cortical excitability, combining it with FES may enhance neuroplasticity. We hypothesized that combining tbTUS with FES would result in increased corticospinal excitability compared to FES alone and lead to greater improvement in fine motor skills as assessed by Nine-Hole Peg Test (NHPT) scores.

METHODS

Fifteen healthy participants underwent two study visits consisting of real or sham tbTUS of the left motor cortex immediately followed by 30 min of FES of the first dorsal interosseous (FDI) and the opponens pollicis (OP) muscles for fine motor function training of the right hand. Motor-evoked potentials (MEPs) were recorded from the right FDI, OP, and abductor digiti minimi (ADM) muscles at baseline (BL), immediately after real or sham tbTUS (T0), immediately after 30 min of FES training (T45), and at 15 (T65) and 30 min (T80) post-FES. NHPT was delivered at BL and at T80.

RESULTS

Data from 14 participants were analyzed. It showed a significant decrease in MEP amplitudes of FDI and OP at T45 following only real tbTUS+FES with a return to BL at T80. No significant changes were seen in the NHPT scores in either condition.

CONCLUSION

Real tbTUS+FES combined with voluntary movement results in immediate corticospinal inhibition with a return to BL at ∼20 min post-stimulation suggestive of homeostatic metaplasticity. These findings highlight the potential of tbTUS+FES as a neuromodulatory intervention, warranting further exploration in neurological conditions for therapeutic applications.

Dynamic changes in human brain connectivity following ultrasound neuromodulation

Non-invasive neuromodulation represents a major opportunity for brain interventions, and transcranial focused ultrasound (FUS) is one of the most promising approaches. However, some challenges prevent the community from fully understanding its outcomes. We aimed to address one of them and unravel the temporal dynamics of FUS effects in humans. Twenty-two healthy volunteers participated in the study. Eleven received FUS in the right inferior frontal cortex while the other 11 were stimulated in the right thalamus. Using a temporal dynamic approach, we compared resting-state fMRI seed-based functional connectivity obtained before and after FUS. We also assessed behavioural changes as measured with a task of reactive motor inhibition. Our findings reveal that the effects of FUS are predominantly time-constrained and spatially distributed in brain regions functionally connected with the directly stimulated area. In addition, mediation analysis highlighted that FUS applied in the right inferior cortex was associated with behavioural alterations which was directly explained by the applied acoustic pressure and the brain functional connectivity change we observed. Our study underscored that the biological effects of FUS are indicative of behavioural changes observed more than an hour following stimulation and are directly related to the applied acoustic pressure.

Investigation of Metaplasticity Associated with Transcranial Focused Ultrasound Neuromodulation in Humans

Low-intensity transcranial focused ultrasound stimulation (TUS) is a novel technique for noninvasive brain stimulation (NIBS). TUS delivered in a theta (5 Hz) burst pattern (tbTUS) induces plasticity in the human primary motor cortex (M1) for 30-60 min, showing promise for therapeutic development. Metaplasticity refers to activity-dependent changes in neural functions governing synaptic plasticity; depotentiation is the reversal of long-term potentiation (LTP) by a subsequent protocol with no effect alone. Metaplasticity can enhance plasticity induction and clinical efficacy of NIBS protocols. In our study, we compared four NIBS protocol combinations to investigate metaplasticity on tbTUS in humans of either sex. We delivered four interventions: (1) sham continuous theta burst stimulation with 150 pulses (cTBS150) followed by real tbTUS (tbTUS only), (2) real cTBS150 followed by sham tbTUS (cTBS only), (3) real cTBS150 followed by real tbTUS (metaplasticity), and (4) real tbTUS followed by real cTBS150 (depotentiation). We measured motor-evoked potential amplitude, short-interval intracortical inhibition, long-interval intracortical inhibition, intracortical facilitation (ICF), and short-interval intracortical facilitation before and up to 90 min after plasticity intervention. Plasticity effects lasted at least 60 min longer when tbTUS was primed with cTBS150 compared with tbTUS alone. Plasticity was abolished when cTBS150 was delivered after tbTUS. cTBS150 alone had no significant effect. No changes in M1 intracortical circuits were observed. Plasticity induction by tbTUS can be modified in manners consistent with homeostatic metaplasticity and depotentiation. This substantiates evidence that tbTUS induces LTP-like processes and suggests that metaplasticity can be harnessed in the therapeutic development of TUS.

Plasticity-Induced Effects of Theta Burst Transcranial Ultrasound Stimulation in Parkinson's Disease

BACKGROUND

Low-intensity transcranial ultrasound stimulation (TUS) is a noninvasive brain stimulation (NIBS) technique with high spatial specificity. Previous studies showed that TUS delivered in a theta burst pattern (tbTUS) increased motor cortex (MI) excitability up to 30 minutes due to long-term potentiation (LTP)-like plasticity. Studies using other forms of NIBS suggested that cortical plasticity may be impaired in patients with Parkinson's disease (PD).

OBJECTIVE

The aim was to investigate the neurophysiological effects of tbTUS in PD patients off and on dopaminergic medications compared to healthy controls.

METHODS

We studied 20 moderately affected PD patients in on and off dopaminergic medication states (7 with and 13 without dyskinesia) and 17 age-matched healthy controls in a case-controlled study. tbTUS was applied for 80 seconds to the MI. Motor-evoked potentials (MEP), short-interval intracortical inhibition (SICI), and short-interval intracortical facilitation (SICF) were recorded at baseline, and at 5 minutes (T5), T30, and T60 after tbTUS. Motor Unified Parkinson's Disease Rating Scale (mUPDRS) was measured at baseline and T60.

RESULTS

tbTUS significantly increased MEP amplitude at T30 compared to baseline in controls and in PD patients on but not in PD patients off medications. SICI was reduced in PD off medications compared to controls. tbTUS did not change in SICI or SICF. The bradykinesia subscore of mUPDRS was reduced at T60 compared to baseline in PD on but not in the off medication state. The presence of dyskinesia did not affect tbTUS-induced plasticity.

CONCLUSIONS

tbTUS-induced LTP plasticity is impaired in PD patients off medications and is restored by dopaminergic medications. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Clinical neurophysiology in the treatment of movement disorders: IFCN handbook chapter

In this review, different aspects of the use of clinical neurophysiology techniques for the treatment of movement disorders are addressed. First of all, these techniques can be used to guide neuromodulation techniques or to perform therapeutic neuromodulation as such. Neuromodulation includes invasive techniques based on the surgical implantation of electrodes and a pulse generator, such as deep brain stimulation (DBS) or spinal cord stimulation (SCS) on the one hand, and non-invasive techniques aimed at modulating or even lesioning neural structures by transcranial application. Movement disorders are one of the main areas of indication for the various neuromodulation techniques. This review focuses on the following techniques: DBS, repetitive transcranial magnetic stimulation (rTMS), low-intensity transcranial electrical stimulation, including transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), and focused ultrasound (FUS), including high-intensity magnetic resonance-guided FUS (MRgFUS), and pulsed mode low-intensity transcranial FUS stimulation (TUS). The main clinical conditions in which neuromodulation has proven its efficacy are Parkinson's disease, dystonia, and essential tremor, mainly using DBS or MRgFUS. There is also some evidence for Tourette syndrome (DBS), Huntington's disease (DBS), cerebellar ataxia (tDCS), and axial signs (SCS) and depression (rTMS) in PD. The development of non-invasive transcranial neuromodulation techniques is limited by the short-term clinical impact of these techniques, especially rTMS, in the context of very chronic diseases. However, at-home use (tDCS) or current advances in the design of closed-loop stimulation (tACS) may open new perspectives for the application of these techniques in patients, favored by their easier use and lower rate of adverse effects compared to invasive or lesioning methods. Finally, this review summarizes the evidence for keeping the use of electromyography to optimize the identification of muscles to be treated with botulinum toxin injection, which is indicated and widely performed for the treatment of various movement disorders.

Transcranial focused ultrasound to V5 enhances human visual motion brain-computer interface by modulating feature-based attention

A brain-computer interface (BCI) enables users to control devices with their minds. Despite advancements, non-invasive BCIs still exhibit high error rates, prompting investigation into the potential reduction through concurrent targeted neuromodulation. Transcranial focused ultrasound (tFUS) is an emerging non-invasive neuromodulation technology with high spatiotemporal precision. This study examines whether tFUS neuromodulation can improve BCI outcomes, and explores the underlying mechanism of action using high-density electroencephalography (EEG) source imaging (ESI). As a result, V5-targeted tFUS significantly reduced the error in a BCI speller task. Source analyses revealed a significantly increase in theta and alpha activities in the tFUS condition at both V5 and downstream in the dorsal visual processing pathway. Correlation analysis indicated that the connection within the dorsal processing pathway was preserved during tFUS stimulation, while the ventral connection was weakened. These findings suggest that V5-targeted tFUS enhances feature-based attention to visual motion.

Effects of the motor cortical theta-burst transcranial-focused ultrasound stimulation on the contralateral motor cortex

Theta-burst transcranial ultrasound stimulation (tbTUS) increases primary motor cortex (M1) excitability for at least 30 min. However, the remote effects of focal M1 tbTUS on the excitability of other cortical areas are unknown. Here, we examined the effects of left M1 tbTUS on right M1 excitability. An 80 s train of active or sham tbTUS was delivered to the left M1 in 20 healthy subjects. Before and after the tbTUS, we measured: (1) corticospinal excitability using motor-evoked potential (MEP) amplitudes from single-pulse transcranial magnetic stimulation (TMS) of left and right M1; (2) interhemispheric inhibition (IHI) from left to right M1 and from right to left M1 using a dual-site paired-pulse TMS paradigm; and (3) intracortical circuits of the right M1 with short-interval intracortical inhibition and intracortical facilitation (ICF) using paired-pulse TMS. Left M1 tbTUS decreased right M1 excitability as shown by decreased MEP amplitudes, increased right M1 ICF and decreased short-interval IHI from left to right hemisphere at interstimulus interval (ISI) of 10 ms but not long-interval IHI at interstimulus interval of 40 ms. The study showed that left M1 tbTUS can change the excitability of remote cortical areas with decreased right M1 excitability and interhemispheric inhibition. The remote effects of tbTUS should be considered when it is used in neuroscience research and as a potential neuromodulation treatment for brain disorders. KEY POINTS: Transcranial ultrasound stimulation (TUS) is a novel non-invasive brain stimulation technique for neuromodulation with the advantages of being able to achieve high spatial resolution and target deep brain structures. A repetitive TUS protocol, with an 80 s train of theta burst patterned TUS (tbTUS), has been shown to increase primary motor cortex (M1) excitability, as well as increase alpha and beta movement-related spectral power in distinct brain regions. In this study, we examined on the effects of the motor cortical tbTUS on the excitability of contralateral M1 measured with MEPs elicited by transcranial magnetic stimulation. We showed that left M1 tbTUS decreased right M1 excitability and left-to-right M1 interhemispheric inhibition, and increased intracortical facilitation of right M1. These results lead to better understand the effects of tbTUS and can help the development of tbTUS for the treatment of neurological and psychiatric disorders and in neuroscience research.

Acupuncture combined with repetitive transcranial magnetic stimulation for the treatment of post-stroke depression: a systematic evaluation and meta-analysis based on a randomised controlled trial

Objective

This study aimed to systematically assess the efficacy of combining acupuncture with repetitive transcranial magnetic stimulation (rTMS) in treating post-stroke depression (PSD).

Methods

We conducted a comprehensive search of eight major domestic and international databases, including the China Knowledge Network, from inception until December 2023. Included were randomized controlled trials that investigated acupuncture combined with rTMS for PSD. The screening process adhered to predetermined inclusion and exclusion criteria, and study quality was assessed using Cochrane Handbook 5.1 guidelines. Meta-analysis was conducted using RevMan 5.4 software.

Results

Twelve studies involving 800 patients were included in the analysis. The meta-analysis showed that acupuncture combined with rTMS significantly improved the clinical effectiveness rate (RR = 1.19, 95% CI: 1.12 to 1.27, p < 0.00001) and reduced scores on several scales: Hamilton Depression Scale (HAMD) (MD = -3.35, 95% CI: -3.79 to -2.90, p < 0.00001), Self-Depression Scale (SDS) (MD = -9.57, 95% CI: -12.26 to -6.89, p < 0.00001), Chinese Medicine Symptom Score (MD = -3.34, 95% CI: -3.76 to -2.91, p < 0.00001), Pittsburgh Sleep Quality Scale (MD = -3.91, 95% CI: -4.58 to -3.25, p < 0.00001), and National Institutes of Health Stroke Scale (NIHSS) (MD = -2.77, 95% CI: -3.21 to -2.32, p < 0.00001). Furthermore, acupuncture combined with rTMS treatment improved cognitive functioning (MMSE, MoCA scores) (p < 0.00001) and ability to perform activities of daily living scores (MD = 10.40, 95% CI: 9.53 to 11.28, p < 0.00001). Additionally, it was found to reduce interleukin 6, tumor necrosis factor alpha, interleukin 1β, and increase 5-hydroxytryptamine and brain-derived neurotrophic factor levels (p < 0.001).

Conclusion

Acupuncture combined with rTMS therapy is recommended for treating PSD, as it effectively improves clinical outcomes, alleviates depressive symptoms, enhances cognitive function, and daily living capabilities, and modulates inflammatory responses and neurotransmitter levels. However, it is important to note that the limitations of the sample size and quality of the included studies warrant the need for more high-quality research to validate these conclusions.

Systematic review registration

INPLASY, Identifier INPLASY202430085.

Sustained reduction of essential tremor with low-power non-thermal transcranial focused ultrasound stimulations in humans

BACKGROUND

Transcranial ultrasound stimulation (TUS) is a non-invasive brain stimulation technique; when skull aberrations are compensated for, this technique allows, with millimetric accuracy, circumvention of the invasive surgical procedure associated with deep brain stimulation (DBS) and the limited spatial specificity of transcranial magnetic stimulation.

OBJECTIVE

/hypothesis: We hypothesize that MR-guided low-power TUS can induce a sustained decrease of tremor power in patients suffering from medically refractive essential tremor.

METHODS

The dominant hand only was targeted, and two anatomical sites were sonicated in this exploratory study: the ventral intermediate nucleus of the thalamus (VIM) and the dentato-rubro-thalamic tract (DRT). Patients (N = 9) were equipped with MR-compatible accelerometers attached to their hands to monitor their tremor in real-time during TUS.

RESULTS

VIM neurostimulations followed by a low-duty cycle (5 %) DRT stimulation induced a substantial decrease in the tremor power in four patients, with a minimum of 89.9 % reduction when compared with the baseline power a few minutes after the DRT stimulation. The only patient stimulated in the VIM only and with a low duty cycle (5 %) also experienced a sustained reduction of the tremor (up to 93.4 %). Four patients (N = 4) did not respond. The temperature at target was 37.2 ± 1.4 °C compared to 36.8 ± 1.4 °C for a 3 cm away control point.

CONCLUSIONS

MR-guided low power TUS can induce a substantial and sustained decrease of tremor power. Follow-up studies need to be conducted to reproduce the effect and better to understand the variability of the response amongst patients. MR thermometry during neurostimulations showed no significant thermal rise, supporting a mechanical effect.

A review of functional neuromodulation in humans using low-intensity transcranial focused ultrasound

Transcranial ultrasonic neuromodulation is a rapidly burgeoning field where low-intensity transcranial focused ultrasound (tFUS), with exquisite spatial resolution and deep tissue penetration, is used to non-invasively activate or suppress neural activity in specific brain regions. Over the past decade, there has been a rapid increase of tFUS neuromodulation studies in healthy humans and subjects with central nervous system (CNS) disease conditions, including a recent surge of clinical investigations in patients. This narrative review summarized the findings of human neuromodulation studies using either tFUS or unfocused transcranial ultrasound (TUS) reported from 2013 to 2023. The studies were categorized into two separate sections: healthy human research and clinical studies. A total of 42 healthy human investigations were reviewed as grouped by targeted brain regions, including various cortical, subcortical, and deep brain areas including the thalamus. For clinical research, a total of 22 articles were reviewed for each studied CNS disease condition, including chronic pain, disorder of consciousness, Alzheimer's disease, Parkinson's disease, depression, schizophrenia, anxiety disorders, substance use disorder, drug-resistant epilepsy, and stroke. Detailed information on subjects/cohorts, target brain regions, sonication parameters, outcome readouts, and stimulatory efficacies were tabulated for each study. In later sections, considerations for planning tFUS neuromodulation in humans were also concisely discussed. With an excellent safety profile to date, the rapid growth of human tFUS research underscores the increasing interest and recognition of its significant potential in the field of non-invasive brain stimulation (NIBS), offering theranostic potential for neurological and psychiatric disease conditions and neuroscientific tools for functional brain mapping.

Neuromodulation techniques - From non-invasive brain stimulation to deep brain stimulation

Over the past 30 years, the field of neuromodulation has witnessed remarkable advancements. These developments encompass a spectrum of techniques, both non-invasive and invasive, that possess the ability to both probe and influence the central nervous system. In many cases neuromodulation therapies have been adopted into standard care treatments. Transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and transcranial ultrasound stimulation (TUS) are the most common non-invasive methods in use today. Deep brain stimulation (DBS), spinal cord stimulation (SCS), and vagus nerve stimulation (VNS), are leading surgical methods for neuromodulation. Ongoing active clinical trials using are uncovering novel applications and paradigms for these interventions.

Effects of different sonication parameters of theta burst transcranial ultrasound stimulation on human motor cortex

BACKGROUND

Theta burst TUS (tbTUS) can induce increased cortical excitability in human, but how different sonication parameters influence the effects are still unknown.

OBJECTIVE

To examine how a range of sonication parameters, including acoustic intensity, pulse repetition frequency, duty cycle and sonication duration, influence the effects of tbTUS on human motor cortical excitability.

METHODS

14 right-handed healthy subjects underwent 8 sessions with different tbTUS parameters in a randomized, cross-over design on separate days. The original tbTUS protocol was studied in one session and one parameter was changed in each of the seven sessions. To examine changes in cortical excitability induced by tbTUS, we measured the motor-evoked potential (MEP) amplitude, resting motor threshold, short-interval intracortical inhibition and intracortical facilitation, as well as short-interval intracortical facilitation before and up to 90 min after tbTUS.

RESULTS

All conditions increased MEP amplitudes except the condition with low acoustic intensity of 10 W/cm2. Pulse repetition frequency of 5 Hz produced higher MEP amplitudes compared to pulse repetition frequencies of 2 and 10 Hz. In addition, higher duty cycles (5%, 10%, and 15%) and longer sonication durations (40, 80, and 120 s) were associated with longer duration of increased MEP amplitudes. Resting motor threshold remained stable in all conditions. For paired-pulse TMS measures, tbTUS reduced short-interval intracortical inhibition and enhanced short-interval intracortical facilitation, but had no effect on intracortical facilitation.

CONCLUSIONS

Ultrasound bursts repeated at theta (∼5 Hz) frequency is optimal to produce increased cortical excitability with the range of 2-10 Hz. Furthermore, there was a dose-response effect regarding duty cycle and sonication duration in tbTUS for plasticity induction. The aftereffects of tbTUS were associated with a shift of the inhibition/excitation balance toward less inhibition and more excitation in the motor cortex. These findings can be used to determine the optimal tbTUS parameters in neuroscience research and treatment of neurological and psychiatric disorders.

The effectiveness and safety of low-intensity transcranial ultrasound stimulation: A systematic review of human and animal studies

Low-intensity transcranial ultrasound stimulation (LITUS) is a novel non-invasive neuromodulation technique. We conducted a systematic review to evaluate current evidence on the efficacy and safety of LITUS neuromodulation. Five databases were searched from inception to May 31, 2023. Randomized controlled human trials and controlled animal studies were included. The neuromodulation effects of LITUS on clinical or pre-clinical, neurophysiological, neuroimaging, histological and biochemical outcomes, and adverse events were summarized. In total, 11 human studies and 44 animal studies were identified. LITUS demonstrated therapeutic efficacy in neurological disorders, psychiatric disorders, pain, sleep disorders and hypertension. LITUS-related changes in neuronal structure and cortical activity were found. From histological and biochemical perspectives, prominent findings included suppressing the inflammatory response and facilitating neurogenesis. No adverse effects were reported in controlled animal studies included in our review, while reversible headache, nausea, and vomiting were reported in a few human subjects. Overall, LITUS alleviates various symptoms and modulates associated brain circuits without major side effects. Future research needs to establish a solid therapeutic framework for LITUS.

Transcranial Focused Ultrasound to V5 Enhances Human Visual Motion Brain-Computer Interface by Modulating Feature-Based Attention

Paralysis affects roughly 1 in 50 Americans. While there is no cure for the condition, brain-computer interfaces (BCI) can allow users to control a device with their mind, bypassing the paralyzed region. Non-invasive BCIs still have high error rates, which is hypothesized to be reduced with concurrent targeted neuromodulation. This study examines whether transcranial focused ultrasound (tFUS) modulation can improve BCI outcomes, and what the underlying mechanism of action might be through high-density electroencephalography (EEG)-based source imaging (ESI) analyses. V5-targeted tFUS significantly reduced the error for the BCI speller task. ESI analyses showed significantly increased theta activity in the tFUS condition at both V5 and downstream the dorsal visual processing pathway. Correlation analysis indicates that the dorsal processing pathway connection was preserved during tFUS stimulation, whereas extraneous connections were severed. These results suggest that V5-targeted tFUS' mechanism of action is to raise the brain's feature-based attention to visual motion.