A double-blind pilot study of transcranial ultrasound (TUS) as a five-day intervention: TUS mitigates worry among depressed participants

Exploiting the mechanical effects of ultrasound for noninvasive therapy

Focused ultrasound is a platform technology capable of eliciting a wide range of biological responses with high spatial precision deep within the body. Although focused ultrasound is already in clinical use for focal thermal ablation of tissue, there has been a recent growth in development and translation of ultrasound-mediated nonthermal therapies. These approaches exploit the physical forces of ultrasound to produce a range of biological responses dependent on exposure conditions. This review discusses recent advances in four application areas that have seen particular growth and have immense clinical potential: brain drug delivery, neuromodulation, focal tissue destruction, and endogenous immune system activation. Owing to the maturation of transcranial ultrasound technology, the brain is a major target organ; however, clinical indications outside the brain are also discussed.

A Comprehensive Review of Low-Intensity Focused Ultrasound Parameters and Applications in Neurologic and Psychiatric Disorders

OBJECTIVES

Low-intensity focused ultrasound (LIFU) is gaining increased interest as a potential therapeutic modality for a range of neuropsychiatric diseases. Current neuromodulation modalities often require a choice between high spatial fidelity or invasiveness. LIFU is unique in this regard because it provides high spatial acuity of both superficial and deep neural structures while remaining noninvasive. This new form of noninvasive brain stimulation may provide exciting potential treatment options for a variety of neuropsychiatric disorders involving aberrant neurocircuitry within deep brain structures, including pain and substance use disorders. Furthermore, LIFU is compatible with noninvasive neuroimaging techniques, such as functional magnetic resonance imaging and electroencephalography, making it a useful tool for more precise clinical neuroscience research to further understand the central nervous system.

MATERIALS AND METHODS

In this study, we provide a review of the most recent LIFU literature covering three key domains: 1) the history of focused ultrasound technology, comparing it with other forms of neuromodulation, 2) the parameters and most up-to-date proposed mechanisms of LIFU, and finally, 3) a consolidation of the current literature to date surrounding the clinical research that has used LIFU for the modification or amelioration of several neuropsychiatric conditions.

RESULTS

The impact of LIFU including poststroke motor changes, pain, mood disorders, disorders of consciousness, dementia, and substance abuse is discussed.

CONCLUSIONS

Although still in its infancy, LIFU is a promising tool that has the potential to change the way we approach and treat neuropsychiatric disorders. In this quickly evolving field, this review serves as a snapshot of the current understanding of LIFU in neuropsychiatric research.

Acoustic Deep Brain Modulation: Enhancing Neuronal Activation and Neurogenesis

BACKGROUND

Non-invasive deep brain modulation (DBM) stands as a promising therapeutic avenue to treat brain diseases. Acoustic DBM represents an innovative and targeted approach to modulate the deep brain, employing techniques such as focused ultrasound and shock waves. Despite its potential, the optimal mechanistic parameters, the effect in the brain and behavioral outcomes of acoustic DBM remains poorly understood.

OBJECTIVE

To establish a robust protocol for the shock wave DBM by optimizing its mechanistic profile of external stimulation, and to assess its efficacy in preclinical settings.

METHODS

We used shockwaves due to their capacity to leverage a broader spectrum of peak intensity (10-127 W/mm2) in contrast to ultrasound (0.1-5.0 W/mm2), thereby enabling a more extensive range of neuromodulation effects. We established various types of shockwave pressure profiles of DBM and compared neural and behavioral responses. To ascertain the anticipated cause of the heightened neural activity response, numerical analysis was employed to examine the mechanical dynamics within the brain.

RESULTS

An optimized profile led to an enhancement in neuronal activity within the hypothalamus of mouse models. The optimized profile in the hippocampus elicited a marked increase in neurogenesis without neuronal damage. Behavioral analyses uncovered a noteworthy reduction in locomotion without significant effects on spatial memory function.

CONCLUSIONS

The present study provides an optimized shock wave stimulation protocol for non-invasive DBM. Our optimized stimulation profile selectively triggers neural functions in the deep brain. Our protocol paves the way for new non-invasive DBM devices to treat brain diseases.

A Physiological Marker for Deep Brain Ultrasonic Neuromodulation

OBJECTIVES

Transcranial ultrasound neuromodulation (TUSN) is a noninvasive and spatially specific therapy that promises to deliver treatments tailored to the specific needs of individuals. To fulfill this promise, each treatment must be modified to adequately correct for variation across individual skulls and neural anatomy. This study examines the use of ultrasound-induced voltage potentials (measured with electroencephalography [EEG]) to guide TUSN therapies.

MATERIALS AND METHODS

We measured EEG responses in two awake nonhuman primates during sonication of 12 targets surrounding two deep brain nuclei, the left and right lateral geniculate nucleus.

RESULTS

We report reliable ultrasound evoked potentials measured with EEG after the deep brain ultrasonic modulation in nonhuman primates. Robust responses are observed after just ten repetitions of the ultrasonic stimuli. Moreover, these potentials are only evoked for specific deep brain targets. Furthermore, a behavioral study in one subject shows a direct correspondence between the target with maximal EEG response and ultrasound-based modulation of visual choice behavior. Thus, this study provides evidence for the feasibility of EEG-based guidance for ultrasound neuromodulation therapies.

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.

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

BACKGROUND

Low-intensity transcranial ultrasound has surged forward as a non-invasive and disruptive tool for neuromodulation with applications in basic neuroscience research and the treatment of neurological and psychiatric conditions.

OBJECTIVE

To provide a comprehensive overview and update of preclinical and clinical transcranial low intensity ultrasound for neuromodulation and emphasize the emerging role of functional brain mapping to guide, better understand, and predict responses.

METHODS

A systematic review was conducted by searching the Web of Science and Scopus databases for studies on transcranial ultrasound neuromodulation, both in humans and animals.

RESULTS

187 relevant studies were identified and reviewed, including 116 preclinical and 71 clinical reports with subjects belonging to diverse cohorts. Milestones of ultrasound neuromodulation are described within an overview of the broader landscape. General neural readouts and outcome measures are discussed, potential confounds are noted, and the emerging use of functional magnetic resonance imaging is highlighted.

CONCLUSION

Ultrasound neuromodulation has emerged as a powerful tool to study and treat a range of conditions and its combination with various neural readouts has significantly advanced this platform. In particular, the use of functional magnetic resonance imaging has yielded exciting inferences into ultrasound neuromodulation and has the potential to advance our understanding of brain function, neuromodulatory mechanisms, and ultimately clinical outcomes. It is anticipated that these preclinical and clinical trials are the first of many; that transcranial low intensity focused ultrasound, particularly in combination with functional magnetic resonance imaging, has the potential to enhance treatment for a spectrum of neurological conditions.

Current state of clinical ultrasound neuromodulation

Unmatched by other non-invasive brain stimulation techniques, transcranial ultrasound (TUS) offers highly focal stimulation not only on the cortical surface but also in deep brain structures. These unique attributes are invaluable in both basic and clinical research and might open new avenues for treating neurological and psychiatric diseases. Here, we provide a concise overview of the expanding volume of clinical investigations in recent years and upcoming research initiatives concerning focused ultrasound neuromodulation. Currently, clinical TUS research addresses a variety of neuropsychiatric conditions, such as pain, dementia, movement disorders, psychiatric conditions, epilepsy, disorders of consciousness, and developmental disorders. As demonstrated in sham-controlled randomized studies, TUS neuromodulation improved cognitive functions and mood, and alleviated symptoms in schizophrenia and autism. Further, preliminary uncontrolled evidence suggests relieved anxiety, enhanced motor functions in movement disorders, reduced epileptic seizure frequency, improved responsiveness in patients with minimally conscious state, as well as pain reduction after neuromodulatory TUS. While constrained by the relatively modest number of investigations, primarily consisting of uncontrolled feasibility trials with small sample sizes, TUS holds encouraging prospects for treating neuropsychiatric disorders. Larger sham-controlled randomized trials, alongside further basic research into the mechanisms of action and optimal sonication parameters, are inevitably needed to unfold the full potential of TUS neuromodulation.

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

Low-intensity Transcranial Ultrasound Stimulation (TUS) is a promising non-invasive technique for deep-brain stimulation and focal neuromodulation. Research with animal models and computational modelling has raised the possibility that TUS can be biased towards enhancing or suppressing neural function. Here, we first conduct a systematic review of human TUS studies for perturbing neural function and alleviating brain disorders. We then collate a set of hypotheses on the directionality of TUS effects and conduct an initial meta-analysis on the human TUS study reported outcomes to date (n = 32 studies, 37 experiments). We find that parameters such as the duty cycle show some predictability regarding whether the targeted area's function is likely to be enhanced or suppressed. Given that human TUS sample sizes are exponentially increasing, we recognize that results can stabilize or change as further studies are reported. Therefore, we conclude by establishing an Iowa-Newcastle (inTUS) resource for the systematic reporting of TUS parameters and outcomes to support further hypothesis testing for greater precision in brain stimulation and neuromodulation with TUS.

Mechanobiological insight into brain diseases based on mechanosensitive channels: Common mechanisms and clinical potential

BACKGROUND

As physical signals, mechanical cues regulate the neural cells in the brain. The mechanosensitive channels (MSCs) perceive the mechanical cues and transduce them by permeating specific ions or molecules across the plasma membrane, and finally trigger a series of intracellular bioelectrical and biochemical signals. Emerging evidence supports that wide-distributed, high-expressed MSCs like Piezo1 play important roles in several neurophysiological processes and neurological disorders.

AIMS

To systematically conclude the functions of MSCs in the brain and provide a novel mechanobiological perspective for brain diseases.

METHOD

We summarized the mechanical cues and MSCs detected in the brain and the research progress on the functional roles of MSCs in physiological conditions. We then concluded the pathological activation and downstream pathways triggered by MSCs in two categories of brain diseases, neurodegenerative diseases and place-occupying damages. Finally, we outlined the methods for manipulating MSCs and discussed their medical potential with some crucial outstanding issues.

RESULTS

The MSCs present underlying common mechanisms in different brain diseases by acting as the "transportation hubs" to transduce the distinct signal patterns: the upstream mechanical cues and the downstream intracellular pathways. Manipulating the MSCs is feasible to alter the complicated downstream processes, providing them promising targets for clinical treatment.

CONCLUSIONS

Recent research on MSCs provides a novel insight into brain diseases. The common mechanisms mediated by MSCs inspire a wide range of therapeutic potentials targeted on MSCs in different brain diseases.

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.

Noninvasive intervention by transcranial ultrasound stimulation: Modulation of neural circuits and its clinical perspectives

Low-intensity focused transcranial ultrasound stimulation (TUS) is an emerging noninvasive technique capable of stimulating both the cerebral cortex and deep brain structures with high spatial precision. This method is recognized for its potential to comprehensively perturb various brain regions, enabling the modulation of neural circuits, in a manner not achievable through conventional magnetic or electrical brain stimulation techniques. The underlying mechanisms of neuromodulation are based on a phenomenon where mechanical waves of ultrasound kinetically interact with neurons, specifically affecting neuronal membranes and mechanosensitive channels. This interaction induces alterations in the excitability of neurons within the stimulated region. In this review, we briefly present the fundamental principles of ultrasound physics and the physiological mechanisms of TUS neuromodulation. We explain the experimental apparatus and procedures for TUS in humans. Due to the focality, the integration of various methods, including magnetic resonance imaging and magnetic resonance-guided neuronavigation systems, is important to perform TUS experiments for precise targeting. We then review the current state of the literature on TUS neuromodulation, with a particular focus on human subjects, targeting both the cerebral cortex and deep subcortical structures. Finally, we outline future perspectives of TUS in clinical applications in psychiatric and neurological fields.

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.

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.

Device for Multifocal Delivery of Ultrasound Into Deep Brain Regions in Humans

Low-intensity focused ultrasound provides the means to noninvasively stimulate or release drugs in specified deep brain targets. However, successful clinical translations require hardware that maximizes acoustic transmission through the skull, enables flexible electronic steering, and provides accurate and reproducible targeting while minimizing the use of MRI. We have developed a device that addresses these practical requirements. The device delivers ultrasound through the temporal and parietal skull windows, which minimize the attenuation and distortions of the ultrasound by the skull. The device consists of 252 independently controlled elements, which provides the ability to modulate multiple deep brain targets at a high spatiotemporal resolution, without the need to move the device or the subject. And finally, the device uses a mechanical registration method that enables accurate deep brain targeting both inside and outside of the MRI. Using this method, a single MRI scan is necessary for accurate targeting; repeated subsequent treatments can be performed reproducibly in an MRI-free manner. We validated these functions by transiently modulating specific deep brain regions in two patients with treatment-resistant depression.

Transcranial focused ultrasound to human rIFG improves response inhibition through modulation of the P300 onset latency

Response inhibition in humans is important to avoid undesirable behavioral action consequences. Neuroimaging and lesion studies point to a locus of inhibitory control in the right inferior frontal gyrus (rIFG). Electrophysiology studies have implicated a downstream event-related potential from rIFG, the fronto-central P300, as a putative neural marker of the success and timing of inhibition over behavioral responses. However, it remains to be established whether rIFG effectively drives inhibition and which aspect of P300 activity uniquely indexes inhibitory control-ERP timing or amplitude. Here, we dissect the connection between rIFG and P300 for inhibition by using transcranial-focused ultrasound (tFUS) to target rIFG of human subjects while they performed a Stop-Signal task. By applying tFUS simultaneously with different task events, we found behavioral inhibition was improved, but only when applied to rIFG simultaneously with a 'stop' signal. Improved inhibition through tFUS to rIFG was indexed by faster stopping times that aligned with significantly shorter N200/P300 onset latencies. In contrast, P300 amplitude was modulated during tFUS across all groups without a paired change in behavior. Using tFUS, we provide evidence for a causal connection between anatomy, behavior, and electrophysiology underlying response inhibition.

Selective Serotonin Reuptake Inhibitors and Other Treatment Modalities for Deep Space Missions

INTRODUCTION: As humankind ventures further into the depths of space, planning is already underway for long-duration exploration missions that will test the bounds of human performance. Deep space travel will include added risk related to stressors from the isolated, confined, and extreme environment that lies outside the boundaries of low Earth orbit. Currently, selective serotonin reuptake inhibitors (SSRIs) are considered the standard of care for many mental health diagnoses, including anxiety and depression; however, SSRIs are also associated with several undesired side effects. The utility of nonpharmacological therapies for the management of behavioral health conditions has not yet been fully explored.METHODS: A comprehensive literature search was performed using PubMed. Relevant articles pertaining to the psychological impacts of isolated, confined, and extreme environments, use of SSRIs in spaceflight, side effects associated with SSRIs, and nonpharmacological treatments for anxiety and depression were reviewed. Over 70 studies were reviewed in total.RESULTS: Reduced bone mineral density, impaired hemostatic function, significant individual variability resulting from gene polymorphisms, and drug-drug interactions are well described adverse effects of SSRIs that may complicate their operational use in the deep space environment. Four alternative therapies for the treatment of anxiety and depression may show promise for long duration missions.DISCUSSION: Although SSRIs have long been considered standard of care treatment for many behavioral health conditions, we cannot trivialize the risk that prolonged pharmacological therapy may pose. The need to mitigate these risks by exploring alternative therapies has never been more relevant.El-Khoury BB, Ray KL, Altchuler SI, Reichard JF, Dukes CH. Selective serotonin reuptake inhibitors and other treatment modalities for deep space missions. Aerosp Med Hum Perform. 2023; 94(11):843-851.

Durable effects of deep brain ultrasonic neuromodulation on major depression: a case report

BACKGROUND

Severe forms of depression have been linked to hyperactivity of the subcallosal cingulate cortex. The ability to stimulate the subcallosal cingulate cortex or associated circuits noninvasively and directly would maximize the number of patients who could receive treatment. To this end, we have developed an ultrasound-based device for effective noninvasive modulation of deep brain circuits. Here we describe an application of this tool to an individual with treatment-resistant depression.

CASE PRESENTATION

A 30-year-old Caucasian woman with severe treatment-resistant non-psychotic depression was recruited into a clinical study approved by the Institutional Review Board of the University of Utah. The patient had a history of electroconvulsive therapy with full remission but without sustained benefit. Magnetic resonance imaging was used to coregister the ultrasound device to the subject's brain anatomy and to evaluate neural responses to stimulation. Brief, 30-millisecond pulses of low-intensity ultrasound delivered into the subcallosal cingulate cortex target every 4 seconds caused a robust decrease in functional magnetic resonance imaging blood-oxygen-level-dependent activity within the target. Following repeated stimulation of three anterior cingulate targets, the patient's depressive symptoms resolved within 24 hours of the stimulation. The patient remained in remission for at least 44 days afterwards.

CONCLUSIONS

This case illustrates the potential for ultrasonic neuromodulation to precisely engage deep neural circuits and to trigger a durable therapeutic reset of those circuits. Trial registration ClinicalTrials.gov, NCT05301036. Registered 29 March 2022, https://clinicaltrials.gov/ct2/show/NCT05301036.

Low-intensity focused ultrasound targeting the nucleus accumbens as a potential treatment for substance use disorder: safety and feasibility clinical trial

Introduction

While current treatments for substance use disorder (SUD) are beneficial, success rates remain low and treatment outcomes are complicated by co-occurring SUDs, many of which are without available medication treatments. Research involving neuromodulation for SUD has recently gained momentum. This study evaluated two doses (60 and 90 W) of Low Intensity Focused Ultrasound (LIFU), targeting the bilateral nucleus accumbens (NAc), in individuals with SUD.

Methods

Four participants (three male), who were receiving comprehensive outpatient treatment for opioid use disorder at the time of enrollment and who also had a history of excessive non-opioid substance use, completed this pilot study. After confirming eligibility, these participants received 10 min sham LIFU followed by 20 min active LIFU (10 min to left then right NAc). Outcomes were the safety, tolerability, and feasibility during the LIFU procedure and throughout the 90-day follow-up. Outcomes also included the impact of LIFU on cue-induced substance craving, assessed via Visual Analog Scale (VAS), both acutely (pre-, during and post-procedure) and during the 90-day follow-up. Daily craving ratings (without cues) were also obtained for one-week prior to and one-week following LIFU.

Results

Both LIFU doses were safe and well-tolerated based on reported adverse events and MRI scans revealed no structural changes (0 min, 24 h, and 1-week post-procedure). For the two participants receiving "enhanced" (90 W) LIFU, VAS craving ratings revealed active LIFU attenuated craving for participants' primary substances of choice relative to sham sonication. For these participants, reductions were also noted in daily VAS craving ratings (0 = no craving; 10 = most craving ever) across the week following LIFU relative to pre-LIFU; Participant #3 pre- vs. post-LIFU: opioids (3.6 ± 0.6 vs. 1.9 ± 0.4), heroin (4.2 ± 0.8 vs. 1.9 ± 0.4), methamphetamine (3.2 ± 0.4 vs. 0.0 ± 0.0), cocaine (2.4 ± 0.6 vs. 0.0 ± 0.0), benzodiazepines (2.8 ± 0.5 vs. 0.0 ± 0.0), alcohol (6.0 ± 0.7 vs. 2.7 ± 0.8), and nicotine (5.6 ± 1.5 vs. 3.1 ± 0.7); Participant #4: alcohol (3.5 ± 1.3 vs. 0.0 ± 0.0) and nicotine (5.0 ± 1.8 vs. 1.2 ± 0.8) (all p's < 0.05). Furthermore, relative to screening, longitudinal reductions in cue-induced craving for several substances persisted during the 90-day post-LIFU follow-up evaluation for all participants.

Discussion

In conclusion, LIFU targeting the NAc was safe and acutely reduced substance craving during the LIFU procedure, and potentially had longer-term impact on craving reductions. While early observations are promising, NAc LIFU requires further investigation in a controlled trial to assess the impact on substance craving and ultimately substance use and relapse.

Inhibition of midfrontal theta with transcranial ultrasound explains greater approach versus withdrawal behavior in humans

Recent reviews highlighted low-intensity transcranial focused ultrasound (TUS) as a promising new tool for non-invasive neuromodulation in basic and applied sciences. Our preregistered double-blind within-subjects study (N = 152) utilized TUS targeting the right prefrontal cortex, which, in earlier work, was found to positively enhance self-reported global mood, decrease negative states of self-reported emotional conflict (anxiety/worrying), and modulate related midfrontal functional magnetic resonance imaging activity in affect regulation brain networks. To further explore TUS effects on objective physiological and behavioral variables, we used a virtual T-maze task that has been established in prior studies to measure motivational conflicts regarding whether participants execute approach versus withdrawal behavior (with free-choice responses via continuous joystick movements) while allowing to record related electroencephalographic data such as midfrontal theta activity (MFT). MFT, a reliable marker of conflict representation on a neuronal level, was of particular interest to us since it has repeatedly been shown to explain related behavior, with relatively low MFT typically preceding approach-like risky behavior and relatively high MFT typically preceding withdrawal-like risk aversion. Our central hypothesis is that TUS decreases MFT in T-maze conflict situations and thereby increases approach and reduces withdrawal. Results indicate that TUS led to significant MFT decreases, which significantly explained increases in approach behavior and decreases in withdrawal behavior. This study expands TUS evidence on a physiological and behavioral level with a large sample size of human subjects, suggesting the promise of further research based on this distinct TUS-MFT-behavior link to influence conflict monitoring and its behavioral consequences. Ultimately, this can serve as a foundation for future clinical work to establish TUS interventions for emotional and motivational mental health.

The Emergence of Functional Ultrasound for Noninvasive Brain-Computer Interface

A noninvasive brain-computer interface is a central task in the comprehensive analysis and understanding of the brain and is an important challenge in international brain-science research. Current implanted brain-computer interfaces are cranial and invasive, which considerably limits their applications. The development of new noninvasive reading and writing technologies will advance substantial innovations and breakthroughs in the field of brain-computer interfaces. Here, we review the theory and development of the ultrasound brain functional imaging and its applications. Furthermore, we introduce latest advancements in ultrasound brain modulation and its applications in rodents, primates, and human; its mechanism and closed-loop ultrasound neuromodulation based on electroencephalograph are also presented. Finally, high-frequency acoustic noninvasive brain-computer interface is prospected based on ultrasound super-resolution imaging and acoustic tweezers.

Investigating the role of the right inferior frontal gyrus in control perception: A double-blind cross-over study using ultrasonic neuromodulation

Being able to control inner and environmental states is a basic need of living creatures. The perception of such control is based on the perceived ratio of outcome probabilities given the presence and the absence of agentic behavior. If an organism believes that options exist to change the probability of a given outcome, control perception (CP) may emerge. Nonetheless, regarding this model, not much is known about how the brain processes CP from this information. This study uses low-intensity transcranial focused ultrasound neuromodulation in a randomized-controlled double blind cross-over design to investigate the impact of the right inferior frontal gyrus of the lateral prefrontal cortex (lPFC) on this process. 39 healthy participants visited the laboratory twice (once in a sham, once in a neuromodulation condition) and rated their control perception regarding a classical control illusion task. EEG alpha and theta power density were analyzed in a hierarchical single trial-based mixed modeling approach. Results indicate that the litFUS neuromodulation changed the processing of stimulus probability without changing CP. Furthermore, neuromodulation of the right lPFC was found to modulate mid-frontal theta by altering its relationship with self-reported effort and worrying. While these data indicate lateral prefrontal sensitivity to stimulus probability, no evidence emerged for the dependency of CP on this processing.

Ultrasonic neuromodulation mediated by mechanosensitive ion channels: current and future

Ultrasound neuromodulation technology is a promising neuromodulation approach, with the advantages of noninvasiveness, high-resolution, deep penetration and good targeting, which aid in circumventing the side effects of drugs and invasive therapeutic interventions. Ultrasound can cause mechanical effects, activate mechanosensitive ion channels and alter neuronal excitability, producing biological effects. The structural determination of mechanosensitive ion channels will greatly contribute to our understanding of the molecular mechanisms underlying mechanosensory transduction. However, the underlying biological mechanism of ultrasonic neuromodulation remains poorly understood. Hence, this review aims to provide an outline of the properties of ultrasound, the structures of specific mechanosensitive ion channels, and their role in ultrasound neuromodulation.

Evaluation of a Novel Acoustic Coupling Medium for Human Low-Intensity Focused Ultrasound Neuromodulation Applications

OBJECTIVE

Single-element low-intensity focused ultrasound (LIFU) is an emerging form of human neuromodulation. Current coupling methods are impractical for clinical bedside use. Here, we evaluate commercially available high-viscosity gel polymer matrices as couplants for human LIFU neuromodulation applications.

METHODS

We first empirically tested the acoustic transmission of three densities at 500 kHz and then subjected the gel with the least acoustic attenuation to further tests of the effect of thickness, frequency, de-gassing and production variability.

RESULTS

The highest-density gel had the lowest acoustic attenuation (3.3%) with low lateral (<0.5 mm) and axial (<2 mm) beam distortion. Different thicknesses of the gel up to 10 mm did not appreciably affect results. The gel polymers exhibited frequency-dependent attenuation at 1 and 3 MHz up to 86.6%, as well as significant beam distortion >4 mm. Poor de-gassing methods also increased pressure attenuation at 500 kHz up to 59.6%. Standardized methods of making these gels should be established to reduce variability.

CONCLUSION

Commercially available de-gassed, high-density gel matrices are a low-cost, easily malleable, low-attenuation and distortion medium for the coupling of single-element LIFU transducers for human neuromodulation applications at 500 kHz.

Transcranial focused ultrasound modulates the emergence of learned helplessness via midline theta modification

BACKGROUND

Helplessness and hopelessness are states closely related to depressive disorders. They ensue following the anticipated absence of valid behavioral options to alleviate an aversive state. One neural structure involved in the detection of such options, is the cingulate cortex (CC), which conveys the evaluation of behavior against the value of its outcome. Accordingly, CC-related EEG measures are thought to correlate to feedback evaluation but also to anxious and conflict-related states, signaling the need for further adaptation to current requirements. Against this background, this study investigated the role of CC functioning in the emergence and prevention of helpless/hopeless states by applying low-intensity transcranial focused ultrasound (litFUS) neuromodulation prior to a learned helplessness task.

METHOD

In a randomized controlled double blind experimental setup with 55 participants, litFUS was used to inhibit the right lateral prefrontal cortex (lPFC), a region closely connected to CC modulation. Participants were instructed to play 8 games of chess against a computer that was unbeatable to them, while an EEG was recorded. Theta oscillation in midline electrodes, playing performance and self-rate measures on cognitive, affective and physiological parameters were assessed.

RESULTS

The results show a considerable influence of litFUS neuromodulation of the lPFC on midline theta activity (Fz and Pz electrode position) which in turn correlated to several psychological variables including self-report data on emotion, cognition, and arousal as well as behavioral measures (playing performance).

LIMITATIONS

Due to the small sample size and sample characteristics, results cannot be generalized to the field of clinical application. A replication of results in larger samples and in context of other sonication parameters is needed to increase the robustness of results and to maximize the efficacy of litFUS application.

CONCLUSIONS

We conclude that the development of learned helplessness/hopelessness could be positively influenced in its course by litFUS neuromodulation of the right lPFC. In line with previous results, especially the posterior midline electrode Pz seems to be an interesting target for further research in this field as theta activity at this electrode is correlated to control perception and motivated behavior. To our knowledge, this is the first study to use neuromodulation to monitor and manipulate the development of helplessness in the laboratory.

Sustained modulation of primate deep brain circuits with focused ultrasonic waves

BACKGROUND

Transcranial focused ultrasound has the potential to noninvasively modulate deep brain circuits and impart sustained, neuroplastic effects.

OBJECTIVE

Bring the approach closer to translations by demonstrating sustained modulation of deep brain circuits and choice behavior in task-performing non-human primates.

METHODS

Low-intensity transcranial ultrasound of 30 s in duration was delivered in a controlled manner into deep brain targets (left or right lateral geniculate nucleus; LGN) of non-human primates while the subjects decided whether a left or a right visual target appeared first. While the animals performed the task, we recorded intracranial EEG from occipital screws. The ultrasound was delivered into the deep brain targets daily for a period of more than 6 months.

RESULTS

The brief stimulation induced effects on choice behavior that persisted up to 15 minutes and were specific to the sonicated target. Stimulation of the left/right LGN increased the proportion of rightward/leftward choices. These effects were accompanied by an increase in gamma activity over visual cortex. The contralateral effect on choice behavior and the increase in gamma, compared to sham stimulation, suggest that the stimulation excited the target neural circuits. There were no detrimental effects on the animals' discrimination performance over the months-long course of the stimulation.

CONCLUSION

This study demonstrates that brief, 30-s ultrasonic stimulation induces neuroplastic effects specifically in the target deep brain circuits, and that the stimulation can be applied daily without detrimental effects. These findings encourage repeated applications of transcranial ultrasound to malfunctioning deep brain circuits in humans with the goal of providing a durable therapeutic reset.

Ultrasound Neuromodulation as a New Brain Therapy

Within the last decade, ultrasound has been "rediscovered" as a technique for brain therapies. Modern technologies allow focusing ultrasound through the human skull for highly focal tissue ablation, clinical neuromodulatory brain stimulation, and targeted focal blood-brain-barrier opening. This article gives an overview on the state-of-the-art of the most recent application: ultrasound neuromodulation as a new brain therapy. Although research centers have existed for decades, the first treatment centers were not established until 2020, and clinical applications are spreading rapidly.

Transcranial ultrasound stimulation modulates the interhemispheric balance of excitability in human motor cortex

Background. Low-intensity transcranial ultrasound stimulation (TUS) could induce both immediate and long-lasting neuromodulatory effects in human brains. Interhemispheric imbalance at prefrontal or motor cortices generally associates with various cognitive decline in aging and mental disorders. However, whether TUS could modulate the interhemispheric balance of excitability in human brain remains unknown.Objective. This study aims to explore whether repetitive TUS (rTUS) intervention can modulate the interhemispheric balance of excitability between bilateral motor cortex (M1) in healthy subjects.Approach. Motor evoked potentials (MEPs) at bilateral M1 were measured at 15 min and 0 min before a 15 min active or sham rTUS intervention on left M1 and at 0 min, 15 min and 30 min after the intervention, and the Chinese version of brief neurocognitive test battery (C-BCT) was conducted before and after the intervention respectively. Cortical excitability was quantified by MEPs, and the long-lasting changes of MEP amplitude was used as an index of plasticity.Results. In the active rTUS group (n= 20), the ipsilateral MEP amplitude increased significantly compared with baselines and lasted for up to 30 min after intervention, while the contralateral MEP amplitude decreased lasting for 15 min, yielding increased laterality between bilateral MEPs. Furthermore, rTUS intervention induced changes in some C-BCT scores, and the changes of scores correlated with the changes of MEP amplitudes induced by rTUS intervention. The sham rTUS group (n= 20) showed no significant changes in MEPs and C-BCT scores. In addition, no participants reported any adverse effects during and after the rTUS intervention, and no obvious temperature increase appeared in skull or brain tissues in simulation.Significance. rTUS intervention modulated the plasticity of ipsilateral M1 and the interhemispheric balance of M1 excitability in human brain, and improved cognitive performance, suggesting a considerable potential of rTUS in clinical interventions.

Clinical Intervention Using Focused Ultrasound (FUS) Stimulation of the Brain in Diverse Neurological Disorders

Various surgical techniques and pharmaceutical treatments have been developed to improve the current technologies of treating brain diseases. Focused ultrasound (FUS) is a new brain stimulation modality that can exert a therapeutic effect on diseased brain cells, with this effect ranging from permanent ablation of the pathological neural circuit to transient excitatory/inhibitory modulation of the neural activity depending on the acoustic energy of choice. With the development of intraoperative imaging technology, FUS has become a clinically available noninvasive neurosurgical option with visual feedback. Over the past 10 years, FUS has shown enormous potential. It can deliver acoustic energy through the physical barrier of the brain and eliminate abnormal brain cells to treat patients with Parkinson's disease and essential tremor. In addition, FUS can help introduce potentially beneficial therapeutics at the exact brain region where they need to be, bypassing the brain's function barrier, which can be applied for a wide range of central nervous system disorders. In this review, we introduce the current FDA-approved clinical applications of FUS, ranging from thermal ablation to blood barrier opening, as well as the emerging applications of FUS in the context of pain control, epilepsy, and neuromodulation. We also discuss the expansion of future applications and challenges. Broadening FUS technologies requires a deep understanding of the effect of ultrasound when targeting various brain structures in diverse disease conditions in the context of skull interface, anatomical structure inside the brain, and pathology.

Transcranial pulse stimulation (TPS) improves depression in AD patients on state-of-the-art treatment

Introduction

Ultrasound‐based brain stimulation is a novel, non‐invasive therapeutic approach to precisely target regions of interest. Data from a first clinical trial of patients with Alzheimer's disease (AD) receiving 2‐4 weeks transcranial pulse stimulation (TPS) have shown memory and cognitive improvements for up to 3 months, despite ongoing state‐of‐the‐art treatment. Importantly, depressive symptoms also improved.

Methods

We analyzed changes in Beck Depression Inventory (BDI‐II) and functional connectivity (FC) changes with functional magnetic resonance imaging in 18 AD patients.

Results

We found significant improvement in BDI‐II after TPS therapy. FC analysis showed a normalization of the FC between the salience network (right anterior insula) and the ventromedial network (left frontal orbital cortex).

Discussion

Stimulation of areas related to depression (including extended dorsolateral prefrontal cortex) appears to alleviate depressive symptoms and induces FC changes in AD patients. TPS may be a novel add‐on therapy for depression in AD and as a neuropsychiatric diagnosis.

Human Ultrasound Neuromodulation: State of the Art

The first human applications of ultrasound in medicine date back to 1939, when Reimar Pohlmann (Berlin, Germany) published data on therapy of neuralgia with ultrasound [...]

Low Intensity Focused Ultrasound for Non-invasive and Reversible Deep Brain Neuromodulation-A Paradigm Shift in Psychiatric Research

This article describes an emerging non-invasive neuromodulatory technology, called low intensity focused ultrasound (LIFU). This technology is potentially paradigm shifting as it can deliver non-invasive and reversible deep brain neuromodulation through acoustic sonication, at millimeter precision. Low intensity focused ultrasound's spatial precision, yet non-invasive nature sets it apart from current technologies, such as transcranial magnetic or electrical stimulation and deep brain stimulation. Additionally, its reversible effects allow for the causal study of deep brain regions implicated in psychiatric illness. Studies to date have demonstrated that LIFU can safely modulate human brain activity at cortical and subcortical levels. Due to its novelty, most researchers and clinicians are not aware of the potential applications and promise of this technique, underscoring the need for foundational papers to introduce the community to LIFU. This mini-review and synthesis of recent advances examines several key papers on LIFU administered to humans, describes the population under study, parameters used, and relevant findings that may guide future research. We conclude with a concise overview of some of the more pressing questions to date, considerations when interpreting new data from an emerging field, and highlight the opportunities and challenges in this exciting new area of study.

Combining brain perturbation and neuroimaging in non-human primates

Brain perturbation studies allow detailed causal inferences of behavioral and neural processes. Because the combination of brain perturbation methods and neural measurement techniques is inherently challenging, research in humans has predominantly focused on non-invasive, indirect brain perturbations, or neurological lesion studies. Non-human primates have been indispensable as a neurobiological system that is highly similar to humans while simultaneously being more experimentally tractable, allowing visualization of the functional and structural impact of systematic brain perturbation. This review considers the state of the art in non-human primate brain perturbation with a focus on approaches that can be combined with neuroimaging. We consider both non-reversible (lesions) and reversible or temporary perturbations such as electrical, pharmacological, optical, optogenetic, chemogenetic, pathway-selective, and ultrasound based interference methods. Method-specific considerations from the research and development community are offered to facilitate research in this field and support further innovations. We conclude by identifying novel avenues for further research and innovation and by highlighting the clinical translational potential of the methods.

Transcranial Focused Ultrasound Enhances Sensory Discrimination Capability through Somatosensory Cortical Excitation

Low-intensity transcranial focused ultrasound (tFUS) has emerged as a non-invasive brain neuromodulation tool with high spatial specificity. Previous studies attributed tFUS-enhanced sensory performance to the ultrasound-induced inhibitory neural effects. However, to date there is no direct evidence validating the neural mechanism underlying ultrasound-mediated somatosensory enhancement. In this study, healthy human subjects (N = 9) were asked to perform tactile vibration frequency discrimination tasks while tFUS was directed onto the primary somatosensory cortex. During this task, we simultaneously recorded 64-channel electroencephalography (EEG) signals and investigated the brain responses at both EEG sensors and source domains by means of electrophysiological source imaging (ESI). The behavioral results indicated that the subjects' discrimination ability was improved by tFUS with an increased percentage of correct responses. EEG and ESI results revealed that tFUS neuromodulation was able to improve sensory discrimination capability through excitatory effects at the targeted sensory cortex.

Effect of Low Intensity Transcranial Ultrasound Stimulation on Neuromodulation in Animals and Humans: An Updated Systematic Review

Background: Although low-intensity transcranial ultrasound stimulation (LI-TUS) has received more recognition for its neuromodulation potential, there remains a crucial knowledge gap regarding the neuromodulatory effects of LI-TUS and its potential for translation as a therapeutic tool in humans.

Objective: In this review, we summarized the findings reported by recently published studies regarding the effect of LI-TUS on neuromodulation in both animals and humans. We also aim to identify challenges and opportunities for the translation process.

Methods: A literature search of PubMed, Medline, EMBASE, and Web of Science was performed from January 2019 to June 2020 with the following keywords and Boolean operators: [transcranial ultrasound OR transcranial focused ultrasound OR ultrasound stimulation] AND [neuromodulation]. The methodological quality of the animal studies was assessed by the SYRCLE's risk of bias tool, and the quality of human studies was evaluated by the PEDro score and the NIH quality assessment tool.

Results: After applying the inclusion and exclusion criteria, a total of 26 manuscripts (24 animal studies and two human studies) out of 508 reports were included in this systematic review. Although both inhibitory (10 studies) and excitatory (16 studies) effects of LI-TUS were observed in animal studies, only inhibitory effects have been reported in primates (five studies) and human subjects (two studies). The ultrasonic parameters used in animal and human studies are different. The SYRCLE quality score ranged from 25 to 43%, with a majority of the low scores related to performance and detection bias. The two human studies received high PEDro scores (9/10).

Conclusion: LI-TUS appears to be capable of targeting both superficial and deep cerebral structures to modulate cognitive or motor behavior in both animals and humans. Further human studies are needed to more precisely define the effective modulation parameters and thereby translate this brain modulatory tool into the clinic.