Long term study of motivational and cognitive effects of low-intensity focused ultrasound neuromodulation in the dorsal striatum of nonhuman primates

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

Introduction

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

Methods

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

Discussion

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

Neural activity to reward and loss predicting treatment outcomes for adults with generalized anxiety disorder: A randomized clinical trial

Aberrant reward processing has been predominantly associated with depressive disorders, with evidence that pre-treatment abnormalities in striatal reward responsiveness relates to treatment outcomes. Emerging research also implicates reward processing differences in anxiety disorders, particularly generalized anxiety disorder (GAD). The current study examined whether pre-treatment reward- and loss-related neural activity predicts symptom improvement with behavioral activation (BA) and exposure therapy (EXP) for GAD. In this randomized clinical trial (ClinicalTrials.gov NCT02807480) conducted from 2016 to 2021, treatment-seeking adults with GAD completed the monetary incentive delay task during functional magnetic resonance imaging pre-treatment, then were randomized to 10-session EXP or BA. The primary outcome measure was the GAD-7. Of 101 participants consented, 69 completed treatment, the 46 completers with quality imaging data were included in analyses (22 EXP, 24 BA; mean 32.7 years, 10.9 % male). A priori region-of-interest analysis revealed that greater left caudate activity during loss receipt predicted greater symptom improvement in EXP, and did not relate to symptom change in BA (F(1, 428)= 5.24, p = 0.023), though this was not significant after correction for multiple comparisons. Whole-brain analysis further identified that greater activity during reward receipt in left frontoparietal regions and anterior insula / ventrolateral prefrontal cortex was associated with better outcomes in BA and worse outcomes in EXP. These findings highlight the role of reward and loss reactivity in GAD treatment. In particular, patients with elevated reactivity to reward salience may benefit most from BA or other reward-focused treatments. Future clinical trials are warranted to further elucidate reward-related predictors of anxiety treatment.

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.

Reward signals in the motor cortex: from biology to neurotechnology

Over the past decade, research has shown that the primary motor cortex (M1), the brain's main output for movement, also responds to rewards. These reward signals may shape motor output in its final stages, influencing movement invigoration and motor learning. In this Perspective, we highlight the functional roles of M1 reward signals and propose how they could guide advances in neurotechnologies for movement restoration, specifically brain-computer interfaces and non-invasive brain stimulation. Understanding M1 reward signals may open new avenues for enhancing motor control and rehabilitation.

Advances in transcranial focused ultrasound neuromodulation for mental disorders

Mental disorders are a major public health concern, affecting millions worldwide. Current treatments have limitations, highlighting the need for novel, effective, and safe interventions. Transcranial focused ultrasound (tFUS), a non-invasive neuromodulation technology, has emerged as a promising tool for treating mental disorders due to its high controllability, precision, and safety. This review summarizes the research progress of tFUS in several major mental disorders, including depression, anxiety, schizophrenia, and substance use disorders (SUDs). Animal studies have demonstrated the efficacy of tFUS in improving psychiatric symptoms and modulating neural circuits through various mechanisms, such as enhancing neuronal activity, synaptic plasticity, and neurotransmitter release. Preliminary clinical trials have also shown the potential of tFUS in alleviating symptoms in patients with treatment-resistant mental disorders. Safety evaluation studies across in vitro, animal, and human levels have supported the overall safety of tFUS under commonly used parameters. tFUS has shown broad application prospects in treating mental disorders, supported by its efficacy in animal models and preliminary clinical trials. By modulating neuronal activity, synaptic plasticity, neurotransmitters, and brain networks, tFUS could improve psychiatric symptoms and regulate neural circuits. However, current research on tFUS in mental disorders is still in its early stages, and further studies are needed to elucidate its mechanisms of action, expand its applications, and conduct large-sample, long-term clinical trials to systematically evaluate its efficacy, protocol optimization, and safety. As an innovative neuromodulation technology, tFUS has the potential to complement conventional therapies and provide new hope for addressing the global challenge of mental disorders.

Optimized ultrasound neuromodulation for non-invasive control of behavior and physiology

Focused ultrasound can non-invasively modulate neural activity, but whether effective stimulation parameters generalize across brain regions and cell types remains unknown. We used focused ultrasound coupled with fiber photometry to identify optimal neuromodulation parameters for four different arousal centers of the brain in an effort to yield overt changes in behavior. Applying coordinate descent, we found that optimal parameters for excitation or inhibition are highly distinct, the effects of which are generally conserved across brain regions and cell types. Optimized stimulations induced clear, target-specific behavioral effects, whereas non-optimized protocols of equivalent energy resulted in substantially less or no change in behavior. These outcomes were independent of auditory confounds and, contrary to expectation, accompanied by a cyclooxygenase-dependent and prolonged reduction in local blood flow and temperature with brain-region-specific scaling. These findings demonstrate that carefully tuned and targeted ultrasound can exhibit powerful effects on complex behavior and physiology.

Scanning ultrasound-mediated memory and functional improvements do not require amyloid-β reduction

A prevalent view in treating age-dependent disorders including Alzheimer's disease (AD) is that the underlying amyloid plaque pathology must be targeted for cognitive improvements. In contrast, we report here that repeated scanning ultrasound (SUS) treatment at 1 MHz frequency can ameliorate memory deficits in the APP23 mouse model of AD without reducing amyloid-β (Aβ) burden. Different from previous studies that had shown Aβ clearance as a consequence of blood-brain barrier (BBB) opening, here, the BBB was not opened as no microbubbles were used. Quantitative SWATH proteomics and functional magnetic resonance imaging revealed that ultrasound induced long-lasting functional changes that correlate with the improvement in memory. Intriguingly, the treatment was more effective at a higher frequency (1 MHz) than at a frequency within the range currently explored in clinical trials in AD patients (286 kHz). Together, our data suggest frequency-dependent bio-effects of ultrasound and a dissociation of cognitive improvement and Aβ clearance, with important implications for the design of trials for AD therapies.

Low-intensity focused ultrasound to the posterior insula reduces temporal summation of pain

BACKGROUND

The insula and dorsal anterior cingulate cortex (dACC) are core brain regions involved in pain processing and central sensitization, a shared mechanism across various chronic pain conditions. Methods to modulate these regions may serve to reduce central sensitization, though it is unclear which target may be most efficacious for different measures of central sensitization.

OBJECTIVE/HYPOTHESIS

Investigate the effect of low-intensity focused ultrasound (LIFU) to the anterior insula (AI), posterior insula (PI), or dACC on conditioned pain modulation (CPM) and temporal summation of pain (TSP).

METHODS

N = 16 volunteers underwent TSP and CPM pain tasks pre/post a 10 min LIFU intervention to either the AI, PI, dACC or Sham stimulation. Pain ratings were collected pre/post LIFU.

RESULTS

Only LIFU to the PI significantly attenuated pain ratings during the TSP protocol. No effects were found for the CPM task for any of the LIFU targets. LIFU pressure modulated group means but did not affect overall group differences.

CONCLUSIONS

LIFU to the PI reduced temporal summation of pain. This may, in part, be due to dosing (pressure) of LIFU. Inhibition of the PI with LIFU may be a future potential therapy in chronic pain populations demonstrating central sensitization. The minimal effective dose of LIFU for efficacious neuromodulation will help to translate LIFU for therapeutic options.

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.

Transspinal Focused Ultrasound Suppresses Spinal Reflexes in Healthy Rats

OBJECTIVES

Low-intensity, focused ultrasound (FUS) is an emerging noninvasive neuromodulation approach, with improved spatial and temporal resolution and penetration depth compared to other noninvasive electrical stimulation strategies. FUS has been used to modulate circuits in the brain and the peripheral nervous system, however, its potential to modulate spinal circuits is unclear. In this study, we assessed the effect of trans-spinal FUS (tsFUS) on spinal reflexes in healthy rats.

MATERIALS AND METHODS

tsFUS targeting different spinal segments was delivered for 1 minute, under anesthesia. Monosynaptic H-reflex of the sciatic nerve, polysynaptic flexor reflex of the sural nerve, and withdrawal reflex tested with a hot plate were measured before, during, and after tsFUS.

RESULTS

tsFUS reversibly suppresses the H-reflex in a spinal segment-, acoustic pressure- and pulse-repetition frequency (PRF)-dependent manner. tsFUS with high PRF augments the degree of homosynaptic depression of the H-reflex observed with paired stimuli. It suppresses the windup of components of the flexor reflex associated with slower, C-afferent, but not faster, A- afferent fibers. Finally, it increases the latency of the withdrawal reflex. tsFUS does not elicit neuronal loss in the spinal cord.

CONCLUSIONS

Our study provides evidence that tsFUS reversibly suppresses spinal reflexes and suggests that tsFUS could be a safe and effective strategy for spinal cord neuromodulation in disorders associated with hyperreflexia, including spasticity after spinal cord injury and painful syndromes.

Dynamical and individualised approach of transcranial ultrasound neuromodulation effects in non-human primates

Low-frequency transcranial ultrasound stimulation (TUS) allows to alter brain functioning with a high spatial resolution and to reach deep targets. However, the time-course of TUS effects remains largely unknown. We applied TUS on three brain targets for three different monkeys: the anterior medial prefrontal cortex, the supplementary motor area and the perigenual anterior cingulate cortex. For each, one resting-state fMRI was acquired between 30 and 150 min after TUS as well as one without stimulation (control). We captured seed-based brain connectivity changes dynamically and on an individual basis. We also assessed between individuals and between targets homogeneity and brain features that predicted TUS changes. We found that TUS prompts heterogenous functional connectivity alterations yet retain certain consistent changes; we identified 6 time-courses of changes including transient and long duration alterations; with a notable degree of accuracy we found that brain alterations could partially be predicted. Altogether, our results highlight that TUS induces heterogeneous functional connectivity alterations. On a more technical point, we also emphasize the need to consider brain changes over-time rather than just observed during a snapshot; to consider inter-individual variability since changes could be highly different from one individual to another.

ENHANCING TRANSCRANIAL FOCUSED ULTRASOUND TREATMENT PLANNING WITH SYNTHETIC CT FROM ULTRA-SHORT ECHO TIME (UTE) MRI: A MULTI-TASK DEEP LEARNING APPROACH

Utilizing a multi-task deep learning framework, this study generated synthetic CT (sCT) images from a limited dataset of Ultrashort echo time (UTE) MRI for transcranial focused ultrasound (tFUS) planning. A 3D Transformer U-Net was employed to produce sCT images that closely replicated actual CT scans, demonstrated by an average Dice coefficient of 0.868 for morphological accuracy. The acoustic simulation with sCT images showed mean focus absolute pressure differences of 8.85±7.29 % for the anterior cingulate cortex, 11.81±8.63 % for the precuneus, and 7.27±3.64 % for the supplemental motor cortex, with focus position discrepancies within 0.9±0.5 mm. These results underscore the efficacy of UTE-MRI as a non-radiative, cost-effective alternative for tFUS planning, with significant potential for clinical application.

Effect of low-intensity focused ultrasound therapy on postpartum uterine involution in puerperal women: A randomized controlled trial

BACKGROUND

Short-term poor uterine involution manifests as uterine contraction weakness. This is one of the important causes of postpartum hemorrhage, posing a serious threat to the mother's life and safety. The study aims to investigate whether low-intensity focused ultrasound (LIFUS) can effectively shorten lochia duration, alleviate postpartum complications, and accelerate uterine involution compared with the sham treatment.

METHODS

A multicenter, concealed, randomized, blinded, and sham-controlled clinical trial was conducted across three medical centers involving 176 subjects, utilizing a parallel group design. Enrollment occurred between October 2019 and September 2020, with a 42-day follow-up period. Participants meeting the inclusion and exclusion criteria based on normal prenatal examinations were randomly divided into the LIFUS group or the sham operation group via computer-generated randomization. Patients in the LIFUS group received usual care with the LIFUS protocol, wherein a LIFUS signal was transmitted to the uterine site through coupling gel, or sham treatment, where no low-intensity ultrasound signal output was emitted. The primary outcome, lochia duration, was assessed via weekly telephonic follow-ups post-discharge. The involution of the uterus, measured by uterine fundus height, served as the secondary outcome.

RESULTS

Among the 256 subjects screened for eligibility, 176 subjects were enrolled and randomly assigned to either the LIFUS group (n = 88) or the Sham group (n = 88). Data on the height of the uterine fundus were obtained from all the patients, with 696 out of 704 measurements (99%) successfully recorded. Overall, a statistically significant difference was noted in time to lochia termination (hazard ratio: 2.65; 95% confidence interval [CI]: 1.82-3.85; P < 0.001). The decline in fundal height exhibited notable discrepancies between the two groups following the second treatment session (mean difference: -1.74; 95% CI: -1.23 to -2.25; P < 0.001) and the third treatment session (mean difference: -3.26; 95% CI: -2.74 to -3.78; P < 0.001) after delivery. None of the subjects had any adverse reactions, such as skin damage or allergies during the treatment.

CONCLUSIONS

This study found that LIFUS treatment can promote uterine involution and abbreviate the duration of postpartum lochia. Ultrasound emerges as a safe and effective intervention, poised to address further clinical inquiries in the domain of postpartum rehabilitation.

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.

High-throughput ultrasound neuromodulation in awake and freely behaving rats

Transcranial ultrasound neuromodulation is a promising potential therapeutic tool for the noninvasive treatment of neuropsychiatric disorders. However, the expansive parameter space and difficulties in controlling for peripheral auditory effects make it challenging to identify ultrasound sequences and brain targets that may provide therapeutic efficacy. Careful preclinical investigations in clinically relevant behavioral models are critically needed to identify suitable brain targets and acoustic parameters. However, there is a lack of ultrasound devices allowing for multi-target experimental investigations in awake and unrestrained rodents. We developed a miniaturized 64-element ultrasound array that enables neurointerventional investigations with within-trial active control targets in freely behaving rats. We first characterized the acoustic field with measurements in free water and with transcranial propagation. We then confirmed in vivo that the array can target multiple brain regions via electronic steering, and verified that wearing the device does not cause significant impairments to animal motility. Finally, we demonstrated the performance of our system in a high-throughput neuromodulation experiment, where we found that ultrasound stimulation of the rat central medial thalamus, but not an active control target, promotes arousal and increases locomotor activity.

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.

Application of transcranial brain stimulation in dementia

The number of patients with dementia grows rapidly as the global population ages, which posits tremendous health-care burden to the society. Only cholinesterase inhibitors and a N-methyl-D-aspartate receptor antagonist have been approved for treating patients with Alzheimer's disease (AD), and their clinical effects remained limited. Medical devices serve as an alternative therapeutic approach to modulating neural activities and enhancing cognitive function. Four major brain stimulation technologies including deep brain stimulation (DBS), transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and transcranial ultrasound stimulation (TUS) have been applied to AD in a clinical trial setting. DBS allows electrical stimulation at the specified nucleus but remains resource-demanding, and after all, an invasive surgery; whereas TMS and tDCS are widely available and affordable but less ideal with respect to localization. The unique physical property of TUS, on the other hand, allows both thermal and mechanical energy to be transduced and focused for neuromodulation. In the context of dementia, using focused ultrasound to induce blood-brain barrier opening for delivering drugs and metabolizing amyloid protein has drawn great attention in recent years. Furthermore, low-intensity pulsed ultrasound has demonstrated its neuroprotective effects in both in vitro and in vivo studies, leading to ongoing clinical trials for AD. The potential and limitation of transcranial brain stimulation for treating patients with dementia would be discussed in this review.

Alteration of functional connectivity in the cortex and major brain networks of non-human primates following focused ultrasound exposure in the dorsal striatum

BACKGROUND

Focused ultrasound (FUS) is a non-invasive neuromodulation technology that is being investigated for potential treatment of neurological and psychiatric disorders. FUS combined with microbubbles can temporarily open the intact blood-brain barrier (BBB) of animals and humans, and facilitate drug delivery. FUS exposure, either with or without microbubbles, has been demonstrated to alter the behavior of non-human primates (NHP), and previous studies have demonstrated the transient and long-term effects of FUS neuromodulation on functional connectivity using resting state functional MRI. The behavioral effects of FUS vary depending on whether or not it is applied in conjunction with microbubbles to open the BBB, but it is unknown whether opening the BBB affects functional connectivity differently than FUS alone.

OBJECTIVE

To compare the effects of applying FUS alone (FUS neuromodulation) and FUS with microbubbles (FUS-BBB opening) on changes of resting state functional connectivity in NHP.

METHODS

We applied 2 min FUS exposure without (neuromodulation) and with microbubbles (BBB opening) in the dorsal striatum of lightly anesthetized non-human primates, and acquired resting state functional MRI 40 min respectively after FUS exposure. The functional connectivity (FC) in the cortex and major brain networks between the two approaches were measured and compared.

RESULTS

When applying FUS exposure to the caudate nucleus of NHP, we found that both FUS neuromodulation can activate FC between caudate and insular cortex, while inhibiting the FC between caudate and motor cortex. FUS-BBB opening can activate FC between the caudate and medial prefrontal cortex, and within the frontotemporal network (FTN). We also found both FUS and FUS-BBB opening can significantly activate FC within the default mode network (DMN).

CONCLUSION

The results suggest applying FUS to a deep brain structure can alter functional connectivity in the DMN and FTN, and that FUS neuromodulation and FUS-mediated BBB opening can have different effects on patterns of functional connectivity.

Physical mechanisms of emerging neuromodulation modalities

One of the ultimate goals of neurostimulation field is to design materials, devices and systems that can simultaneously achieve safe, effective and tether-free operation. For that, understanding the working mechanisms and potential applicability of neurostimulation techniques is important to develop noninvasive, enhanced, and multi-modal control of neural activity. Here, we review direct and transduction-based neurostimulation techniques by discussing their interaction mechanisms with neurons via electrical, mechanical, and thermal means. We show how each technique targets modulation of specific ion channels (e.g. voltage-gated, mechanosensitive, heat-sensitive) by exploiting fundamental wave properties (e.g. interference) or engineering nanomaterial-based systems for efficient energy transduction. Overall, our review provides a detailed mechanistic understanding of neurostimulation techniques together with their applications toin vitro, in vivo, and translational studies to guide the researchers toward developing more advanced systems in terms of noninvasiveness, spatiotemporal resolution, and clinical applicability.

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.

Modulation effects of low-intensity transcranial ultrasound stimulation on the neuronal firing activity and synaptic plasticity of mice

Low-intensity transcranial ultrasound stimulation (TUS) has been effective in modulating several neurological and psychiatric disorders. However, how TUS modulates neuronal firing activity and synaptic plasticity remains unclear. Thus, we behaviorally tested the whisker-dependent novel object discrimination ability in mice after ultrasound stimulation and examined the cortical neuronal firing activity and synaptic plasticity in awake mice after ultrasound stimulation by two-photon fluorescence imaging. The current study presented the following results: (1) TUS could significantly improve the whisker-dependent new object discrimination ability of mice, suggesting that their learning and memory abilities were significantly enhanced; (2) TUS significantly enhanced neuronal firing activity; and (3) TUS increased the growth rate of dendritic spines in the barrel cortex, but did not promote the extinction of dendritic spines, resulting in enhanced synaptic plasticity. The above results indicate that TUS can improve the learning and memory ability of mice and enhance the neuronal firing activity and synaptic plasticity that are closely related to it. This study provides a research basis for the application of ultrasound stimulation in the treatment of learning- and memory-related diseases.

Low-Intensity Focused Ultrasound Neuromodulation for Stroke Recovery: A Novel Deep Brain Stimulation Approach for Neurorehabilitation?

Stroke as the leading cause of adult long-term disability and has a significant impact on patients, society and socio-economics. Non-invasive brain stimulation (NIBS) approaches such as transcranial magnetic stimulation (TMS) or transcranial electrical stimulation (tES) are considered as potential therapeutic options to enhance functional reorganization and augment the effects of neurorehabilitation. However, non-invasive electrical and magnetic stimulation paradigms are limited by their depth focality trade-off function that does not allow to target deep key brain structures critically important for recovery processes. Transcranial ultrasound stimulation (TUS) is an emerging approach for non-invasive deep brain neuromodulation. Using non-ionizing, ultrasonic waves with millimeter-accuracy spatial resolution, excellent steering capacity and long penetration depth, TUS has the potential to serve as a novel non-invasive deep brain stimulation method to establish unprecedented neuromodulation and novel neurorehabilitation protocols. The purpose of the present review is to provide an overview on the current knowledge about the neuromodulatory effects of TUS while discussing the potential of TUS in the field of stroke recovery, with respect to existing NIBS methods. We will address and discuss critically crucial open questions and remaining challenges that need to be addressed before establishing TUS as a new clinical neurorehabilitation approach for motor stroke recovery.

Ultrasound as a versatile tool for short- and long-term improvement and monitoring of brain function

Treating the brain with focused ultrasound (FUS) at low intensities elicits diverse responses in neurons, astroglia, and the extracellular matrix. In combination with intravenously injected microbubbles, FUS also opens the blood-brain barrier (BBB) and facilitates focal drug delivery. However, an incompletely understood cellular specificity and a wide parameter space currently limit the optimal application of FUS in preclinical and human studies. In this perspective, we discuss how different FUS modalities can be utilized to achieve short- and long-term improvements, thereby potentially treating brain disorders. We review the ongoing efforts to determine which parameters induce neuronal inhibition versus activation and how mechanoreceptors and signaling cascades are activated to induce long-term changes, including memory improvements. We suggest that optimal FUS treatments may require different FUS modalities and devices, depending on the targeted brain area or local pathology, and will be greatly enhanced by new techniques for monitoring FUS efficacy.

Pulsed Focused Ultrasound Reduces Hippocampal Volume Loss and Improves Behavioral Performance in the Kainic Acid Rat Model of Epilepsy

Focused ultrasound (FUS) has the potential to modulate regional brain excitability and possibly aid seizure control; however, effects on behavior of FUS used as a seizure therapy are unknown. This study explores behavioral effects and hippocampal restoration induced by pulsed FUS in a kainic acid (KA) animal model of temporal lobe epilepsy. Twenty-nine male Sprague-Dawley rats were observed for 20 weeks with anatomical magnetic resonance imaging (MRI) and behavioral performance evaluations, comprising measures of anxiety, limb usage, sociability, and memory. FUS targeted to the right hippocampus was given 9 and 14 weeks after KA was delivered to the right amygdala. Ultrasound pulsations were delivered with the acoustic settings of 0.25 of mechanical index, 0.5 W/cm2 of intensity spatial peak temporal average (ISPTA), 100 Hz of pulse repetition frequency, and 30% of duty cycle, during three consecutive pulse trains of 10 min separated by 5-min rests. Controls included normal animals with sham injections and KA-exposed animals without FUS exposure. Longitudinal MRI observations showed that FUS substantially protected hippocampal and striatal structures from KA-induced atrophy. KA alone increased anxiety, impaired contralateral limb usage, and reduced sociability and learning. Two courses of FUS sonications partially ameliorated these impairments by enhancing exploring and learning, balancing limb usage, and increasing social interaction. The histology results indicated that two sonications enhanced neuroprotection effect and decreased the inflammation markers induced by KA. This study supports existence of both neuroprotective and beneficial behavioral effects from low-intensity pulsed ultrasound in the KA animal model of epilepsy.

Personalized Definition of Surgical Targets in Major Depression and Obsessive-Compulsive Disorder: A Potential Role for Low-Intensity Focused Ultrasound?

Major Depressive Disorder (MDD) and Obsessive-Compulsive Disorder (OCD) are common and potentially incapacitating conditions. Even when recognized and adequately treated, in over a third of patients with these conditions the response to first-line pharmacological and psychotherapeutic measures is not satisfactory. After more assertive measures including pharmacological augmentation (and in the case of depression, transcranial magnetic stimulation, electroconvulsive therapy, or treatment with ketamine or esketamine), a significant number of individuals remain severely symptomatic. In these persons, different ablation and deep-brain stimulation (DBS) psychosurgical techniques have been employed. However, apart from the cost and potential morbidity associated with surgery, on average only about half of patients show adequate response, which limits the widespread application of these potentially life-saving interventions. Possible reasons are considered for the wide variation in outcomes across different series of patients with MDD or OCD exposed to ablative or DBS psychosurgery, including interindividual anatomical and etiological variability. Low-intensity focused ultrasound (LIFU) is an emerging technique that holds promise in its ability to achieve anatomically circumscribed, noninvasive, and reversible neuromodulation of deep brain structures. A possible role for LIFU in the personalized presurgical definition of neuromodulation targets in the individual patient is discussed, including a proposed roadmap for clinical trials addressed at testing whether this technique can help to improve psychosurgical outcomes.

Alteration of functional connectivity in the cortex and major brain networks of non-human primates following focused ultrasound exposure

Focused ultrasound (FUS) is a non-invasive neuromodulation technology that is being investigated for potential treatment of neurological and psychiatric disorders. Focused ultrasound combined with microbubbles can temporarily open the intact blood-brain barrier (BBB) of animals and humans, and facilitate drug delivery. FUS exposure, either with or without microbubbles, has been demonstrated to alter the behavior of non-human primates, and previous work has demonstrated transient and long-term effects of FUS neuromodulation on functional connectivity using resting state functional MRI. However, it is unknown whether opening the BBB affects functional connectivity differently than FUS alone. Thus we applied FUS alone (neuromodulation) and FUS with microbubbles (BBB opening) in the dorsal striatum of lightly anesthetized non-human primates, and compared changes in functional connectivity in major brain networks. We found different alteration patterns between FUS neuromodulation and FUS-mediated BBB opening in several cortical areas, and we also found that applying FUS to a deep brain structure can alter functional connectivity in the default mode network and frontotemporal network.

Effects of focused ultrasound pulse duration on stimulating cortical and subcortical motor circuits in awake sheep

Low-intensity transcranial focused ultrasound (tFUS) offers new functional neuromodulation opportunities, enabling stimulation of cortical as well as deep brain areas with high spatial resolution. Brain stimulation of awake sheep, in the absence of the confounding effects of anesthesia on brain function, provides translational insight into potential human applications with safety information supplemented by histological analyses. We examined the effects of tFUS pulsing parameters, particularly regarding pulse durations (PDs), on stimulating the cortical motor area (M1) and its thalamic projection in unanesthetized, awake sheep (n = 8). A wearable tFUS headgear, custom-made for individual sheep, enabled experiments to be conducted without using anesthesia. FUS stimuli, each 200 ms long, were delivered to the M1 and the thalamus using three different PDs (0.5, 1, and 2 ms) with the pulse repetition frequency (PRF) adjusted to maintain a 70% duty cycle at a derated in situ spatial-peak temporal-average intensity (Ispta) of 3.6 W/cm2. Efferent electromyography (EMG) responses to stimulation were quantified from both hind limbs. Group-averaged EMG responses from each of the hind limbs across the experimental conditions revealed selective responses from the hind limb contralateral to sonication. The use of 0.5 and 1 ms PDs generated higher EMG signal amplitudes compared to those obtained using a 2 ms PD. Faster efferent response was also observed from thalamic stimulation than that from stimulating the M1. Post-sonication behavioral observation and histological assessment performed 24 h and 1 month after sonication were not indicative of any abnormalities. The results suggest the presence of pulsing scheme-dependent effects of tFUS on brain stimulation and attest its safety in awake large animals.

Safety of Clinical Ultrasound Neuromodulation

Transcranial ultrasound holds much potential as a safe, non-invasive modality for navigated neuromodulation, with low-intensity focused ultrasound (FUS) and transcranial pulse stimulation (TPS) representing the two main modalities. While neuroscientific and preclinical applications have received much interest, clinical applications are still relatively scarce. For safety considerations, the current literature is largely based on guidelines for ultrasound imaging that uses various physical parameters to describe the ultrasound pulse form and expected bioeffects. However, the safety situation for neuromodulation is inherently different. This article provides an overview of relevant ultrasound parameters with a focus on bioeffects relevant for safe clinical applications. Further, a retrospective analysis of safety data for clinical TPS applications in patients is presented.

Effects of Anesthesia on Cerebral Blood Flow and Functional Connectivity of Nonhuman Primates

Nonhuman primates (NHPs) are the closest living relatives of humans and play a critical and unique role in neuroscience research and pharmaceutical development. General anesthesia is usually required in neuroimaging studies of NHPs to keep the animal from stress and motion. However, the adverse effects of anesthesia on cerebral physiology and neural activity are pronounced and can compromise the data collection and interpretation. Functional connectivity is frequently examined using resting-state functional MRI (rsfMRI) to assess the functional abnormality in the animal brain under anesthesia. The fMRI signal can be dramatically suppressed by most anesthetics in a dose-dependent manner. In addition, rsfMRI studies may be further compromised by inter-subject variations when the sample size is small (as seen in most neuroscience studies of NHPs). Therefore, proper use of anesthesia is strongly demanded to ensure steady and consistent physiology maintained during rsfMRI data collection of each subject. The aim of this review is to summarize typical anesthesia used in rsfMRI scans of NHPs and the effects of anesthetics on cerebral physiology and functional connectivity. Moreover, the protocols with optimal rsfMRI data acquisition and anesthesia procedures for functional connectivity study of macaque monkeys are introduced.

32 Element Piezoelectric Micromachined Ultrasound Transducer (PMUT) Phased Array for Neuromodulation

Interest in utilizing ultrasound (US) transducers for non-invasive neuromodulation treatment, including for low intensity transcranial focused ultrasound stimulation (tFUS), has grown rapidly. The most widely demonstrated US transducers for tFUS are either bulk piezoelectric transducers or capacitive micromachine transducers (CMUT) which require high voltage excitation to operate. In order to advance the development of the US transducers towards small, portable devices for safe tFUS at large scale, a low voltage array of US transducers with beam focusing and steering capability is of interest. This work presents the design methodology, fabrication, and characterization of 32-element phased array piezoelectric micromachined ultrasound transducers (PMUT) using 1.5 μm thick Pb(Zr_0.52 Ti_0.48)O₃ films doped with 2 mol% Nb. The electrode/piezoelectric/electrode stack was deposited on a silicon on insulator (SOI) wafer with a 2 μm silicon device layer that serves as the passive elastic layer for bending-mode vibration. The fabricated 32-element PMUT has a central frequency at 1.4 MHz. Ultrasound beam focusing and steering (through beamforming) was demonstrated where the array was driven with 14.6 V square unipolar pulses. The PMUT generated a maximum peak-to-peak focused acoustic pressure output of 0.44 MPa at a focal distance of 20 mm with a 9.2 mm and 1 mm axial and lateral resolution, respectively. The maximum pressure is equivalent to a spatial-peak pulse-average intensity of 1.29 W/cm², which is suitable for tFUS application.