Focused ultrasound-mediated suppression of chemically-induced acute epileptic EEG activity

Advances in using ultrasound to regulate the nervous system

Ultrasound is a mechanical vibration with a frequency greater than 20 kHz. Due to its high spatial resolution, good directionality, and convenient operation in neural regulation, it has recently received increasing attention from scientists. However, the mechanism by which ultrasound regulates the nervous system is still unclear. This article mainly explores the possible mechanisms of ultrasound's mechanical effects, cavitation effects, thermal effects, and the rise of sonogenetics. In addition, the essence of action potential and its relationship with ultrasound were also discussed. Traditional theory treats nerve impulses as pure electrical signals, similar to cable theory. However, this theory cannot explain the phenomenon of inductance and cell membrane bulging out during the propagation of action potential. Therefore, the flexoelectric effect of cell membrane and soliton model reveal that action potential may also be a mechanical wave. Finally, we also elaborated the therapeutic effect of ultrasound on nervous system disease such as epilepsy, Parkinson's disease, and Alzheimer's disease.

Effects of Transcranial Ultrasound Stimulation on Blood Oxygen Metabolism and Brain Rhythms in Nitroglycerin-Induced Migraine Mice

OBJECTIVES

In this study, we aimed to investigate the regulatory mechanism of transcranial ultrasound stimulation (TUS) on nitroglycerin-induced migraine in mice.

MATERIALS AND METHODS

The experiment was divided into four groups, namely, the normal saline control group (n = 9), ultrasound stimulation control group (n = 6), nitroglycerin-induced migraine group (n = 9), and ultrasound stimulation group (n = 9). The behavior, blood oxygen metabolism, and brain rhythm distribution of the four groups were analyzed.

RESULTS

We found that after TUS, the movement time and speed of mice with migraine are modulated to those of the control groups, and the number of head scratching and grooming events is significantly reduced. TUS increased the deoxygenated hemoglobin, and the power of the 4-to-40 Hz frequency band of local field potentials in the cortex of migraine mice. TUS also decreased the expression of plasma calcitonin gene-related peptide and cortical c-Fos protein.

CONCLUSIONS

Ultrasound stimulation can regulate brain rhythm and blood oxygen metabolism and reduce migraine symptoms in mice. The regulatory mechanism may be related to reducing calcitonin gene-related peptide in blood vessels.

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.

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.

Non-invasive suppression of the human nucleus accumbens (NAc) with transcranial focused ultrasound (tFUS) modulates the reward network: a pilot study

Background

The nucleus accumbens (NAc) is a key node of the brain reward circuit driving reward-related behavior. Dysregulation of NAc has been demonstrated to contribute to pathological markers of addiction in substance use disorder (SUD) making it a potential therapeutic target for brain stimulation. Transcranial focused ultrasound (tFUS) is an emerging non-invasive brain stimulation approach that can modulate deep brain regions with a high spatial resolution. However, there is currently no evidence showing how the brain activity of NAc and brain functional connectivity within the reward network neuromodulated by tFUS on the NAc.

Methods

In this pilot study, we carried out a single-blind, sham-controlled clinical trial using functional magnetic resonance imaging (fMRI) to investigate the underlying mechanism of tFUS neuromodulating the reward network through NAc in ten healthy adults. Specifically, the experiment consists of a 20-min concurrent tFUS/fMRI scan and two 24-min resting-state fMRI before and after the tFUS session.

Results

Firstly, our results demonstrated the feasibility and safety of 20-min tFUS on NAc. Additionally, our findings demonstrated that bilateral NAc was inhibited during tFUS on the left NAc compared to sham. Lastly, increased functional connectivity between the NAc and medial prefrontal cortex (mPFC) was observed after tFUS on the left NAc, but no changes for the sham group.

Conclusion

Delivering tFUS to the NAc can modulate brain activations and functional connectivity within the reward network. These preliminary findings suggest that tFUS could be potentially a promising neuromodulation tool for the direct and non-invasive management of the NAc and shed new light on the treatment for SUD and other brain diseases that involve reward processing.

Functional ultrasound (fUS) imaging of displacement-guided focused ultrasound (FUS) neuromodulation in mice

Focused ultrasound (FUS) stimulation is a promising neuromodulation technique with the merits of non-invasiveness, high spatial resolution, and deep penetration depth. However, simultaneous imaging of FUS-induced brain tissue displacement and the subsequent effect of FUS stimulation on brain hemodynamics has proven challenging thus far. In addition, earlier studies lack in situ confirmation of targeting except for the magnetic resonance imaging-guided FUS system-based studies. The purpose of this study is 1) to introduce a fully ultrasonic approach to in situ target, modulate neuronal activity, and monitor the resultant neuromodulation effect by respectively leveraging displacement imaging, FUS, and functional ultrasound (fUS) imaging, and 2) to investigate FUS-evoked cerebral blood volume (CBV) response and the relationship between CBV and displacement. We performed displacement imaging on craniotomized mice to confirm the in targeting for neuromodulation site. We recorded hemodynamic responses evoked by FUS and fUS revealed an ipsilateral CBV increase that peaks at 4 s post-FUS. We saw a stronger hemodynamic activation in the subcortical region than cortical, showing good agreement with the brain elasticity map that can also be obtained using a similar methodology. We observed dose-dependent CBV response with peak CBV, activated area, and correlation coefficient increasing with ultrasonic dose. Furthermore, by mapping displacement and hemodynamic activation, we found that displacement colocalizes and linearly correlates with CBV increase. The findings presented herein demonstrated that FUS evokes ipsilateral hemodynamic activation in cortical and subcortical depths and the evoked hemodynamic responses colocalized and correlate with FUS-induced displacement. We anticipate that our findings will help consolidate accurate targeting as well as an understanding of how FUS displaces brain tissue and affects cerebral hemodynamics.

Repetitive pulsed-wave ultrasound stimulation suppresses neural activity by modulating ambient GABA levels via effects on astrocytes

Ultrasound is highly biopermeable and can non-invasively penetrate deep into the brain. Stimulation with patterned low-intensity ultrasound can induce sustained inhibition of neural activity in humans and animals, with potential implications for research and therapeutics. Although mechanosensitive channels are involved, the cellular and molecular mechanisms underlying neuromodulation by ultrasound remain unknown. To investigate the mechanism of action of ultrasound stimulation, we studied the effects of two types of patterned ultrasound on synaptic transmission and neural network activity using whole-cell recordings in primary cultured hippocampal cells. Single-shot pulsed-wave (PW) or continuous-wave (CW) ultrasound had no effect on neural activity. By contrast, although repetitive CW stimulation also had no effect, repetitive PW stimulation persistently reduced spontaneous recurrent burst firing. This inhibitory effect was dependent on extrasynaptic-but not synaptic-GABAA receptors, and the effect was abolished under astrocyte-free conditions. Pharmacological activation of astrocytic TRPA1 channels mimicked the effects of ultrasound by increasing the tonic GABAA current induced by ambient GABA. Pharmacological blockade of TRPA1 channels abolished the inhibitory effect of ultrasound. These findings suggest that the repetitive PW low-intensity ultrasound used in our study does not have a direct effect on neural function but instead exerts its sustained neuromodulatory effect through modulation of ambient GABA levels via channels with characteristics of TRPA1, which is expressed in astrocytes.

The effect of transcranial ultrasound pulse repetition frequency on sustained inhibition in the human primary motor cortex: A double-blind, sham-controlled study

BACKGROUND

Non-invasive brain stimulation techniques such as transcranial magnetic stimulation and transcranial direct current stimulation hold promise for inducing brain plasticity. However, their limited precision may hamper certain applications. In contrast, Transcranial Ultrasound Stimulation (TUS), known for its precision and deep brain targeting capabilities, requires further investigation to establish its efficacy in producing enduring effects for treating neurological and psychiatric disorders.

OBJECTIVE

To investigate the enduring effects of different pulse repetition frequencies (PRF) of TUS on motor corticospinal excitability.

METHODS

T1-, T2-weighted, and zero echo time magnetic resonance imaging scans were acquired from 21 neurologically healthy participants for neuronavigation, skull reconstruction, and the performance of transcranial ultrasound and thermal modelling. The effects of three different TUS PRFs (10, 100, and 1000 Hz) with a constant duty cycle of 10 % on corticospinal excitability in the primary motor cortex were assessed using TMS-induced motor evoked potentials (MEPs). Each PRF and sham condition was evaluated on separate days, with measurements taken 5-, 30-, and 60-min post-TUS.

RESULTS

A significant decrease in MEP amplitude was observed with a PRF of 10 Hz (p = 0.007), which persisted for at least 30 min, and with a PRF of 100 Hz (p = 0.001), lasting over 60 min. However, no significant changes were found for the PRF of 1000 Hz and the sham conditions.

CONCLUSION

This study highlights the significance of PRF selection in TUS and underscores its potential as a non-invasive approach to reduce corticospinal excitability, offering valuable insights for future clinical applications.

Ultrasound Deep Brain Stimulation Regulates Food Intake and Body Weight in Mice

Given the widespread occurrence of obesity, new strategies are urgently needed to prevent, halt and reverse this condition. We proposed a noninvasive neurostimulation tool, ultrasound deep brain stimulation (UDBS), which can specifically modulate the hypothalamus and effectively regulate food intake and body weight in mice. Fifteen-min UDBS of hypothalamus decreased 41.4% food intake within 2 hours. Prolonged 1-hour UDBS significantly decreased daily food intake lasting 4 days. UDBS also effectively restrained body weight gain in leptin-receptor knockout mice (Sham: 96.19%, UDBS: 58.61%). High-fat diet (HFD) mice treated with 4-week UDBS (15 min / 2 days) reduced 28.70% of the body weight compared to the Sham group. Meanwhile, UDBS significantly modulated glucose-lipid metabolism and decreased the body fat. The potential mechanism is that ultrasound actives pro-opiomelanocortin (POMC) neurons in the hypothalamus for reduction of food intake and body weight. These results provide a noninvasive tool for controlling food intake, enabling systematic treatment of obesity.

Neuropsychiatric Behavioral Assessments in Mice After Acute and Long-Term Treatments of Low-Intensity Pulsed Ultrasound

Introduction: To evaluate whether both acute and chronic low-intensity pulsed ultrasound (LIPUS) affect brain functions of healthy male and female mice. Methods: Ultrasound (frequency: 1.5 MHz; pulse: 1.0 kHz; spatial average temporal average (SATA) intensity: 25 mW/cm2; and pulse duty cycle: 20%) was applied at mouse head in acute test for 20 minutes, and in chronic experiment for consecutive 10 days, respectively. Behaviors were then evaluated. Results: Both acute and chronic LIPUS at 25 mW/cm2 exposure did not affect the abilities of movements, mating, social interaction, and anxiety-like behaviors in the male and female mice. However, physical restraint caused struggle-like behaviors and short-time memory deficits in chronic LIPUS groups in the male mice. Conclusion: LIPUS at 25 mW/cm2 itself does not affect brain functions, while physical restraint for LIPUS therapy elicits struggle-like behaviors in the male mice. An unbound helmet targeted with ultrasound intensity at 25-50 mW/cm2 is proposed for clinical brain disease therapy.

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

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

Bidirectional Neuronal Control of Epileptiform Activity by Repetitive Transcranial Focused Ultrasound Stimulations

Repetitive stimulation procedures are used in neuromodulation techniques to induce persistent excitatory or inhibitory brain activity. The directivity of modulation is empirically regulated by modifying the stimulation length, interval, and strength. However, bidirectional neuronal modulations using ultrasound stimulations are rarely reported. This study presents bidirectional control of epileptiform activities with repetitive transcranial-focused ultrasound stimulations in a rat model of drug-induced acute epilepsy. It is found that repeated transmission of elongated (40 s), ultra-low pressure (0.25 MPa) ultrasound can fully suppress epileptic activities in electro-encephalography and cerebral blood volume measurements, while the change in bursting intervals from 40 to 20 s worsens epileptic activities even with the same burst length. Furthermore, the suppression induced by 40 s long bursts is transformed to excitatory states by a subsequent transmission. Bidirectional modulation of epileptic seizures with repeated ultrasound stimulation is achieved by regulating the changes in glutamate and γ-Aminobutyric acid levels, as confirmed by measurements of expressed c-Fos and GAD65 and multitemporal analysis of neurotransmitters in the interstitial fluid obtained via microdialysis.

Ultrasonic therapies for seizures and drug-resistant epilepsy

Ultrasonic therapy is an increasingly promising approach for the treatment of seizures and drug-resistant epilepsy (DRE). Therapeutic focused ultrasound (FUS) uses thermal or nonthermal energy to either ablate neural tissue or modulate neural activity through high- or low-intensity FUS (HIFU, LIFU), respectively. Both HIFU and LIFU approaches have been investigated for reducing seizure activity in DRE, and additional FUS applications include disrupting the blood-brain barrier in the presence of microbubbles for targeted-drug delivery to the seizure foci. Here, we review the preclinical and clinical studies that have used FUS to treat seizures. Additionally, we review effective FUS parameters and consider limitations and future directions of FUS with respect to the treatment of DRE. While detailed studies to optimize FUS applications are ongoing, FUS has established itself as a potential noninvasive alternative for the treatment of DRE and other neurological disorders.

Patient-specific modeling for guided rehabilitation of stroke patients: the BrainX3 use-case

BrainX3 is an interactive neuroinformatics platform that has been thoughtfully designed to support neuroscientists and clinicians with the visualization, analysis, and simulation of human neuroimaging, electrophysiological data, and brain models. The platform is intended to facilitate research and clinical use cases, with a focus on personalized medicine diagnostics, prognostics, and intervention decisions. BrainX3 is designed to provide an intuitive user experience and is equipped to handle different data types and 3D visualizations. To enhance patient-based analysis, and in keeping with the principles of personalized medicine, we propose a framework that can assist clinicians in identifying lesions and making patient-specific intervention decisions. To this end, we are developing an AI-based model for lesion identification, along with a mapping of tract information. By leveraging the patient's lesion information, we can gain valuable insights into the structural damage caused by the lesion. Furthermore, constraining whole-brain models with patient-specific disconnection masks can allow for the detection of mesoscale excitatory-inhibitory imbalances that cause disruptions in macroscale network properties. Finally, such information has the potential to guide neuromodulation approaches, assisting in the choice of candidate targets for stimulation techniques such as Transcranial Ultrasound Stimulation (TUS), which modulate E-I balance, potentiating cortical reorganization and the restoration of the dynamics and functionality disrupted due to the lesion.

MR-Guided Focused Ultrasound for Refractory Epilepsy: Where Are We Now?

Epilepsy is one of the most common neurological diseases in both adults and children. Despite improvements in medical care, 20 to 30% of patients are still resistant to the best medical treatment. The quality of life, neurologic morbidity, and even mortality of patients are significantly impacted by medically intractable epilepsy. Nowadays, conservative therapeutic approaches consist of increasing medication dosage, changing to a different anti-seizure drug as monotherapy, and combining different antiseizure drugs using an add-on strategy. However, such measures may not be sufficient to efficiently control seizure recurrence. Resective surgery, ablative procedures and non-resective neuromodulatory (deep-brain stimulation, vagus nerve stimulation) treatments are the available treatments for these kinds of patients. However, invasive procedures may involve lengthy inpatient stays for the patients, risks of long-term neurological impairment, general anesthesia, and other possible surgery-related complications (i.e., hemorrhage or infection). In the last few years, MR-guided focused ultrasound (MRgFUS) has been proposed as an emerging treatment for neurological diseases because of technological advancements and the goal of minimally invasive neurosurgery. By outlining the current knowledge obtained from both preclinical and clinical studies and discussing the technical opportunities of this therapy for particular epileptic phenotypes, in this perspective review, we explore the various mechanisms and potential applications (thermoablation, blood-brain barrier opening for drug delivery, neuromodulation) of high- and low-intensity ultrasound, highlighting possible novel strategies to treat drug-resistant epileptic patients who are not eligible or do not accept currently established surgical approaches. Taken together, the available studies support a possible role for lesional treatment over the anterior thalamus with high-intensity ultrasound and neuromodulation of the hippocampus via low-intensity ultrasound in refractory epilepsy. However, more studies, likely conceiving epilepsy as a network disorder and bridging together different scales and modalities, are required to make ultrasound delivery strategies meaningful, effective, and safe.

A Miniature Ultrasound Source for Neural Modulation

This work describes a unique ultrasound (US) exposure system designed to create very localized ( [Formula: see text]) sound fields at operating frequencies that are currently being used for preclinical US neuromodulation. This system can expose small clusters of neuronal tissue, such as cell cultures or intact brain structures in target animal models, opening up opportunities to examine possible mechanisms of action. We modified a dental descaler and drove it at a resonance frequency of 96 kHz, well above its nominal operating point of 28 kHz. A ceramic microtip from an ultrasonic wire bonder was attached to the end of the applicator, creating a 100- [Formula: see text] point source. The device was calibrated with a polyvinylidene difluoride (PVDF) membrane hydrophone, in a novel, air-backed, configuration. The experimental results were confirmed by simulation using a monopole model. The results show a consistent decaying sound field from the tip, well-suited to neural stimulation. The system was tested on an existing neurological model, Drosophila melanogaster, which has not previously been used for US neuromodulation experiments. The results show brain-directed US stimulation induces or suppresses motor actions, demonstrated through synchronized tracking of fly limb movements. These results provide the basis for ongoing and future studies of US interaction with neuronal tissue, both at the level of single neurons and intact organisms.

A transducer positioning method for transcranial focused ultrasound treatment of brain tumors

Purpose

As a non-invasive method for brain diseases, transcranial focused ultrasound (tFUS) offers higher spatial precision and regulation depth. Due to the altered path and intensity of sonication penetrating the skull, the focus and intensity in the skull are difficult to determine, making the use of ultrasound therapy for cancer treatment experimental and not widely available. The deficiency can be effectively addressed by numerical simulation methods, which enable the optimization of sonication modulation parameters and the determination of precise transducer positioning.

Methods

A 3D skull model was established using binarized brain CT images. The selection of the transducer matrix was performed using the radius positioning (RP) method after identifying the intracranial target region. Simulations were performed, encompassing acoustic pressure (AP), acoustic field, and temperature field, in order to provide compelling evidence of the safety of tFUS in sonication-induced thermal effects.

Results

It was found that the angle of sonication path to the coronal plane obtained at all precision and frequency models did not exceed 10° and 15° to the transverse plane. The results of thermal effects illustrated that the peak temperatures of tFUS were 43.73°C, which did not reach the point of tissue degeneration. Once positioned, tFUS effectively delivers a Full Width at Half Maximum (FWHM) stimulation that targets tumors with diameters of up to 3.72 mm in a one-off. The original precision model showed an attenuation of 24.47 ± 6.13 mm in length and 2.40 ± 1.42 mm in width for the FWHM of sonication after penetrating the skull.

Conclusion

The vector angles of the sonication path in each direction were determined based on the transducer positioning results. It has been suggested that when time is limited for precise transducer positioning, fixing the transducer on the horizontal surface of the target region can also yield positive results for stimulation. This framework used a new transducer localization method to offer a reliable basis for further research and offered new methods for the use of tFUS in brain tumor-related research.

Development and validation of a computational method to predict unintended auditory brainstem response during transcranial ultrasound neuromodulation in mice

BACKGROUND

Transcranial ultrasound stimulation (TUS) is a promising noninvasive neuromodulation modality. The inadvertent and unpredictable activation of the auditory system in response to TUS obfuscates the interpretation of non-auditory neuromodulatory responses.

OBJECTIVE

The objective was to develop and validate a computational metric to quantify the susceptibility to unintended auditory brainstem response (ABR) in mice premised on time frequency analyses of TUS signals and auditory sensitivity.

METHODS

Ultrasound pulses with varying amplitudes, pulse repetition frequencies (PRFs), envelope smoothing profiles, and sinusoidal modulation frequencies were selected. Each pulse's time-varying frequency spectrum was differentiated across time, weighted by the mouse hearing sensitivity, then summed across frequencies. The resulting time-varying function, computationally predicting the ABR, was validated against experimental ABR in mice during TUS with the corresponding pulse.

RESULTS

There was a significant correlation between experimental ABRs and the computational predictions for 19 TUS signals (R2 = 0.97).

CONCLUSIONS

To reduce ABR in mice during in vivo TUS studies, 1) reduce the amplitude of a rectangular continuous wave envelope, 2) increase the rise/fall times of a smoothed continuous wave envelope, and/or 3) change the PRF and/or duty cycle of a rectangular or sinusoidal pulsed wave to reduce the gap between pulses and increase the rise/fall time of the overall envelope. This metric can aid researchers performing in vivo mouse studies in selecting TUS signal parameters that minimize unintended ABR. The methods for developing this metric can be adapted to other animal models.

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.

A phased array ultrasound system with a robotic arm for neuromodulation

BACKGROUND

Ultrasonic neuromodulation (UNMOD) provides a non-invasive brain stimulation. However, the high-resolution region-specificity of UNMOD with a single element transducer combined with a mechanical positioning system could have limits due to the intrinsic positioning error from mechanical systems.

OBJECTIVE/HYPOTHESIS

A phased array system could lead to highly selective neuromodulation with electronic control.

METHODS

A specialized phased-array system with a robotic arm is implemented for a rhesus monkey model. Various primary motor cortex areas related to tail, hand, and mouth were stimulated with a 200 μm step size. The ultrasonic parameters were ISPTA of 840 mW/cm2, pulse repetition frequency of 100 Hz, and a 5% duty factor at 600 kHz. The induced movement were recorded and analyzed.

RESULTS

Separate digits, mouth, and tongue motions were successfully induced by electronically controlling the focus. The identical body part movement could be induced when the focus was moved back to the identical primary motor cortex with electronic control. Accordingly, the reproducibility of UNMOD could be partially validated with rhesus monkey model.

CONCLUSION

A phased-array system appears to have a potential for the non-invasive and region-selective neuromodulation method.

Transcranial focused ultrasound stimulation of cortical and thalamic somatosensory areas in human

The effects of transcranial focused ultrasound (FUS) stimulation of the primary somatosensory cortex and its thalamic projection (i.e., ventral posterolateral nucleus) on the generation of electroencephalographic (EEG) responses were evaluated in healthy human volunteers. Stimulation of the unilateral somatosensory circuits corresponding to the non-dominant hand generated EEG evoked potentials across all participants; however, not all perceived stimulation-mediated tactile sensations of the hand. These FUS-evoked EEG potentials (FEP) were observed from both brain hemispheres and shared similarities with somatosensory evoked potentials (SSEP) from median nerve stimulation. Use of a 0.5 ms pulse duration (PD) sonication given at 70% duty cycle, compared to the use of 1 and 2 ms PD, elicited more distinctive FEP peak features from the hemisphere ipsilateral to sonication. Although several participants reported hearing tones associated with FUS stimulation, the observed FEP were not likely to be confounded by the auditory sensation based on a separate measurement of auditory evoked potentials (AEP) to tonal stimulation (mimicking the same repetition frequency as the FUS stimulation). Off-line changes in resting-state functional connectivity (FC) associated with thalamic stimulation revealed that the FUS stimulation enhanced connectivity in a network of sensorimotor and sensory integration areas, which lasted for at least more than an hour. Clinical neurological evaluations, EEG, and neuroanatomical MRI did not reveal any adverse or unintended effects of sonication, attesting its safety. These results suggest that FUS stimulation may induce long-term neuroplasticity in humans, indicating its neurotherapeutic potential for various neurological and neuropsychiatric conditions.

Low-Intensity Pulsed Ultrasound Neuromodulation of a Rodent's Spinal Cord Suppresses Motor Evoked Potentials

OBJECTIVE

Here we investigate the ability of low-intensity ultrasound (LIUS) applied to the spinal cord to modulate the transmission of motor signals.

METHODS

Male adult Sprague-Dawley rats (n = 10, 250-300 g, 15 weeks old) were used in this study. Anesthesia was initially induced with 2% isoflurane carried by oxygen at 4 L/min via a nose cone. Cranial, upper extremity, and lower extremity electrodes were placed. A thoracic laminectomy was performed to expose the spinal cord at the T11 and T12 vertebral levels. A LIUS transducer was coupled to the exposed spinal cord, and motor evoked potentials (MEPs) were acquired each minute for either 5- or 10-minutes of sonication. Following the sonication period, the ultrasound was turned off and post-sonication MEPs were acquired for an additional 5 minutes.

RESULTS

Hindlimb MEP amplitude significantly decreased during sonication in both the 5- (p < 0.001) and 10-min (p = 0.004) cohorts with a corresponding gradual recovery to baseline. Forelimb MEP amplitude did not demonstrate any statistically significant changes during sonication in either the 5- (p = 0.46) or 10-min (p = 0.80) trials.

CONCLUSION

LIUS applied to the spinal cord suppresses MEP signals caudal to the site of sonication, with recovery of MEPs to baseline after sonication.

SIGNIFICANCE

LIUS can suppress motor signals in the spinal cord and may be useful in treating movement disorders driven by excessive excitation of spinal neurons.

Global sonication of the human intracranial space via a jumbo planar transducer

Contrary to conditioning a Focused Ultrasound (FUS) beam to sonicate a localized region of the human brain, the goal of this investigation was to explore the prospect of distributing homogeneous ultrasound energy over the entire brain space with a large cranium-wide ultrasound beam. Recent ultrasound preclincal studies utilizing large or whole brain stimulation regions create a demand for expanding the treatment envelope of transcranial pulsed-low intensity ultrasound towards Global Brain Sonication (GBS) for potential human investigation. Here, we conduct ultrasound field characterizations when transmitting pulsed ultrasound through human skull specimens using a 1-3 piezocomposite planar transducer operating at 464 kHz with an active single-element surface of 30 × 30 cm. Through computational simulation and hydrophone scanning methodology, ultrasound wave behavior and dose homogeneity in the brain space were evaluated under various trajectories of sonication using the planar transducer. Clinically relevant pulse parameters used for transcranial therapeutic ultrasound applications were used in the experiments. Simulations and empirical testing revealed that dose homogeneity and acoustic intensity over the brain space are influenced by sonication trajectory, skull lens effects, and acoustic wave reflections. The transducer can emit a spatial peak pulse average intensity of 4.03 W/cm² (0.24 MPa) measured in the free-field at 464 kHz with electrical power of 1 kW. The simulation showed that approximately 99 % of the cranial volume was exposed with <30 % of the maximum external acoustic intensity being transmitted into the skull. The transmission loss across all sonication trajectories is similar to previously reported FUS studies. A marker for GBS dose homogeneity is introduced to score the ultrasound pressure field uniformity in the intracranial space. Results of this study identify the initial challenges of exposing the entire human brain space with ultrasound using a large cranium-wide sonication beam intended for global brain therapeutic modulation.

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.

Multifocal skull-compensated transcranial focused ultrasound system for neuromodulation applications based on acoustic holography

Transcranial focused ultrasound stimulation is a promising therapeutic modality for human brain disorders because of its noninvasiveness, long penetration depth, and versatile spatial control capability through beamforming and beam steering. However, the skull presents a major hurdle for successful applications of ultrasound stimulation. Specifically, skull-induced focal aberration limits the capability for accurate and versatile targeting of brain subregions. In addition, there lacks a fully functional preclinical neuromodulation system suitable to conduct behavioral studies. Here, we report a miniature ultrasound system for neuromodulation applications that is capable of highly accurate multiregion targeting based on acoustic holography. Our work includes the design and implementation of an acoustic lens for targeting brain regions with compensation for skull aberration through time-reversal recording and a phase conjugation mirror. Moreover, we utilize MEMS and 3D-printing technology to implement a 0.75-g lightweight neuromodulation system and present in vivo characterization of the packaged system in freely moving mice. This preclinical system is capable of accurately targeting the desired individual or multitude of brain regions, which will enable versatile and explorative behavior studies using ultrasound neuromodulation to facilitate widespread clinical adoption.

Transcranial focused ultrasound-mediated unbinding of phenytoin from plasma proteins for suppression of chronic temporal lobe epilepsy in a rodent model

The efficacy of many anti-epileptic drugs, including phenytoin (PHT), is reduced by plasma protein binding (PPB) that sequesters therapeutically active drug molecules within the bloodstream. An increase in systemic dose elevates the risk of drug side effects, which demands an alternative technique to increase the unbound concentration of PHT in a region-specific manner. We present a low-intensity focused ultrasound (FUS) technique that locally enhances the efficacy of PHT by transiently disrupting its binding to albumin. We first identified the acoustic parameters that yielded the highest PHT unbinding from albumin among evaluated parameter sets using equilibrium dialysis. Then, rats with chronic mesial temporal lobe epilepsy (mTLE) received four sessions of PHT injection, each followed by 30 min of FUS delivered to the ictal region, across 2 weeks. Two additional groups of mTLE rats underwent the same procedure, but without receiving PHT or FUS. Assessment of electrographic seizure activities revealed that FUS accompanying administration of PHT effectively reduced the number and mean duration of ictal events compared to other conditions, without damaging brain tissue or the blood-brain barrier. Our results demonstrated that the FUS technique enhanced the anti-epileptic efficacy of PHT in a chronic mTLE rodent model by region-specific PPB disruption.

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.

Modulation effect of non-invasive transcranial ultrasound stimulation in an ADHD rat model

Objective.Previous studies have demonstrated that transcranial ultrasound stimulation (TUS) with noninvasive high penetration and high spatial resolution has an effective neuromodulatory effect on neurological diseases. Attention deficit hyperactivity disorder (ADHD) is a persistent neurodevelopmental disorder that severely affects child health. However, the neuromodulatory effects of TUS on ADHD have not been reported to date. This study aimed to investigate the neuromodulatory effects of TUS on ADHD.Approach.TUS was performed in ADHD model rats for two consecutive weeks, and the behavioral improvement of ADHD, neural activity of ADHD from neurons and neural oscillation levels, and the plasma membrane dopamine transporter and brain-derived neurotrophic factor (BDNF) in the brains of ADHD rats were evaluated.Main results.TUS can improve cognitive behavior in ADHD rats, and TUS altered neuronal firing patterns and modulated the relative power and sample entropy of local field potentials in the ADHD rats. In addition, TUS can also enhance BDNF expression in the brain tissues.Significance. TUS has an effective neuromodulatory effect on ADHD and thus has the potential to clinically improve cognitive dysfunction in ADHD.

Modulation effect of mouse hippocampal neural oscillations by closed-loop transcranial ultrasound stimulation

Objective. Closed-loop transcranial ultrasound stimulation (TUS) can be applied at a specific time according to the state of neural activity to achieve timely and precise neuromodulation and improve the modulation effect. In a previous study, we found that closed-loop TUS at the peaks and troughs of the theta rhythm in the mouse hippocampus was able to increase the absolute power and decrease the relative power of the theta rhythm of local field potentials (LFPs) independent of the peaks and troughs of the stimulus. However, it remained unclear whether the modulation effect of this closed-loop TUS-induced mouse hippocampal neural oscillation depended on the peaks and troughs of the theta rhythm.Approach. In this study, we used ultrasound with different stimulation modes and durations to stimulate the peaks (peak stimulation) and troughs (trough stimulation) of the hippocampal theta rhythm. The LFPs in the area of ultrasound stimulation were recorded and the amplitudes and power spectra of the theta rhythm before and after ultrasound stimulation were analyzed.Main results. The results showed that (a) the relative change in amplitude of theta rhythm decreases as the number of stimulation trials under peak stimulation increases; (b) the relative change in the absolute power of the theta rhythm decreases as the number of stimulation trials under peak stimulation increases; (c) the relative change in amplitude of the theta rhythm increases nonlinearly with the stimulation duration (SD) under peak stimulation, and; (d) the relative change in absolute power exhibits a nonlinear increase with SD under peak stimulation.Significance. These results suggest that the modulation effect of closed-loop TUS on theta rhythm is dependent on the stimulation mode and duration under peak stimulation. TUS has the potential to precisely modulate theta rhythm-related neural activity.

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.

Therapeutic ultrasound: The future of epilepsy surgery?

Epilepsy is one of the leading neurological diseases in both adults and children and in spite of advancement in medical treatment, 20 to 30% of patients remain refractory to current medical treatment. Medically intractable epilepsy has a real impact on a patient's quality of life, neurologic morbidity and even mortality. Actual therapy options are an increase in drug dosage, radiosurgery, resective surgery and non-resective neuromodulatory treatments (deep brain stimulation, vagus nerve stimulation). Resective, thermoablative or neuromodulatory surgery in the treatment of epilepsy are invasive procedures, sometimes requiring long stay-in for the patients, risks of permanent neurological deficit, general anesthesia and other potential surgery-related complications such as a hemorrhage or an infection. Radiosurgical approaches can trigger radiation necrosis, brain oedema and transient worsening of epilepsy. With technology-driven developments and pursuit of minimally invasive neurosurgery, transcranial MR-guided focused ultrasound has become a valuable treatment for neurological diseases. In this critical review, we aim to give the reader a better understanding of current advancement for ultrasound in the treatment of epilepsy. By outlining the current understanding gained from both preclinical and clinical studies, this article explores the different mechanisms and potential applications (thermoablation, blood brain barrier disruption for drug delivery, neuromodulation and cortical stimulation) of high and low intensity ultrasound and compares the various possibilities available to patients with intractable epilepsy. Technical limitations of therapeutic ultrasound for epilepsy surgery are also detailed and discussed.

Modulation effect of low-intensity transcranial ultrasound stimulation on REM and NREM sleep

Previous studies have shown that modulating neural activity can affect rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. Low-intensity transcranial ultrasound stimulation (TUS) can effectively modulate neural activity. However, the modulation effect of TUS on REM and NREM sleep is still unclear. In this study, we used ultrasound to stimulate motor cortex and hippocampus, respectively, and found the following: (i) In healthy mice, TUS increased the NREM sleep ratio and decreased the REM sleep ratio, and altered the relative power and sample entropy of the delta band and spindle in NREM sleep and that of the theta and gamma bands in REM sleep. (ii) In sleep-deprived mice, TUS decreased the ratio of REM sleep or the relative power of the theta band during REM sleep. (iii) In sleep-disordered Alzheimer’s disease (AD) mice, TUS increased the total sleep time and the ratio of NREM sleep and modulated the relative power and the sample entropy of the delta and spindle bands during NREM and that of the theta band during REM sleep. These results demonstrated that TUS can effectively modulate REM and NREM sleep and that modulation effect depends on the sleep state of the samples, and can improve sleep in sleep-disordered AD mice.

Harnessing Ultrasound for Targeting Drug Delivery to the Brain and Breaching the Blood–Brain Tumour Barrier

Despite significant advances in developing drugs to treat brain tumours, achieving therapeutic concentrations of the drug at the tumour site remains a major challenge due to the presence of the blood–brain barrier (BBB). Several strategies have evolved to enhance brain delivery of chemotherapeutic agents to treat tumours; however, most approaches have several limitations which hinder their clinical utility. Promising studies indicate that ultrasound can penetrate the skull to target specific brain regions and transiently open the BBB, safely and reversibly, with a high degree of spatial and temporal specificity. In this review, we initially describe the basics of therapeutic ultrasound, then detail ultrasound-based drug delivery strategies to the brain and the mechanisms by which ultrasound can improve brain tumour therapy. We review pre-clinical and clinical findings from ultrasound-mediated BBB opening and drug delivery studies and outline current therapeutic ultrasound devices and technologies designed for this purpose.

Wired for sound: The effect of sound on the epileptic brain

Sound waves are all around us resonating at audible and inaudible frequencies. Our ability to hear is crucial in providing information and enabling interaction with our environment. The human brain generates neural oscillations or brainwaves through synchronised electrical impulses. In epilepsy these brainwaves can change and form rhythmic bursts of abnormal activity outwardly appearing as seizures. When two waveforms meet, they can superimpose onto one another forming constructive, destructive or mixed interference. The effects of audible soundwaves on epileptic brainwaves has been largely explored with music. The Mozart Sonata for Two Pianos in D major, K. 448 has been examined in a number of studies where significant clinical and methodological heterogeneity exists. These studies report variable reductions in seizures and interictal epileptiform discharges. Treatment effects of Mozart Piano Sonata in C Major, K.545 and other composer interventions have been examined with some musical exposures, for example Hayden's Symphony No. 94 appearing pro-epileptic. The underlying anti-epileptic mechanism of Mozart music is currently unknown, but interesting research is moving away from dopamine reward system theories to computational analysis of specific auditory parameters. In the last decade several studies have examined inaudible low intensity focused ultrasound as a neuro-modulatory intervention in focal epilepsy. Whilst acute and chronic epilepsy rodent model studies have consistently demonstrated an anti-epileptic treatment effect this is yet to be reported within large scale human trials. Inaudible infrasound is of concern since at present there are no reported studies on the effects of exposure to infrasound on epilepsy. Understanding the impact of infrasound on epilepsy is critical in an era where sustainable energies are likely to increase exposure.

Preventive and Therapeutic Effects of Low-Intensity Ultrasound Stimulation on Migraine in Rats

This study sought to systematically evaluate the prophylactic and therapeutic effects of low-intensity transcranial ultrasound stimulation on migraine in rats. We used video recordings to assess the head scratching behavior and laser speckle contrast imaging to record the changes in cerebral blood flow velocity of freely moving rats in a healthy group, migraine group, migraine group with ultrasound prevention, and migraine group with ultrasound therapy. Results demonstrated that (1) head scratching during migraine attacks in rats was accompanied by an decrease in cerebral blood flow; (2) both ultrasound prevention and therapy significantly reduced the number of head scratches but did not reduce the cerebral blood flow velocity; and (3) the number of head scratches in the ultrasound stimulation groups was not affected by the auditory effect. These results reveal that low-intensity ultrasound has the potential to be used clinically in the prevention and therapeutic treatment of migraine.

Transcranial ultrasound stimulation applied in ischemic stroke rehabilitation: A review

Ischemic stroke is a serious medical condition that is caused by cerebral vascular occlusion and leads to neurological dysfunction. After stroke, patients suffer from long-term sensory, motor and cognitive impairment. Non-invasive neuromodulation technology has been widely studied in the field of stroke rehabilitation. Transcranial ultrasound stimulation (TUS), as a safe and non-invasive technique with deep penetration ability and a tiny focus, is an emerging technology. It can produce mechanical and thermal effects by delivering sound waves to brain tissue that can induce the production of neurotrophic factors (NFs) in the brain, and reduce cell apoptosis and the inflammatory response. TUS, which involves application of an acoustic wave, can also dissolve blood clots and be used to deliver therapeutic drugs to the ischemic region. TUS has great potential in the treatment of ischemic stroke. Future advancements in imaging and parameter optimization will improve the safety and efficacy of this technology in the treatment of ischemic stroke.

Pulsed-Focused Ultrasound Provides Long-Term Suppression of Epileptiform Bursts in the Kainic Acid-Induced Epilepsy Rat Model

Focused ultrasound (FUS) has potential utility for modulating regional brain excitability and possibly aiding seizure control; however, the duration of any beneficial effect is unknown. This study explores the efficacy and time course of a short series of pulsed FUS in suppressing EEG epileptiform spikes/bursts in a kainic acid (KA) animal model of temporal lobe epilepsy. Forty-four male Sprague-Dawley rats were recorded for 14 weeks with EEG while software calculated EEG numbers of epileptiform spikes and bursts (≥ 3 spikes/s). Four regimens of FUS given in a single session at week 7 were evaluated, with mechanical index (MI) ranging from 0.25 to 0.75, intensity spatial peak temporal average (ISPTA) from 0.1 to 2.8 W per cm2, duty cycle from 1 to 30%, and three consecutive pulse trains for 5 or 10 min each. Controls included sham injections in four and KA without FUS in eleven animals. Histological analysis investigated tissue effects. All animals receiving KA evidenced EEG spikes, averaging 10,378 ± 1651 spikes per 8 h and 1255 ± 199 bursts per 8 h by weeks 6-7. The KA-only group showed a 30% of increase in spikes and bursts by week 14. Compared to the KA-only group, spike counts were reduced by about 25%, burst counts by about 33%, and burst durations by about 50% with FUS. Behavioral seizures were not analyzed, but electrographic seizures longer than 10 s declined up to 70% after some FUS regimens. Repeated-measure ANOVA showed a significant effect of higher intensity and longer sonication duration FUS treatment using 0.75-MI, ISPTA 2.8 W/cm2, 30% duty cycle for 10-min sonications (group effect, F (4, 15) = 6.321, p < 0.01; interaction effect, F (44, 165) = 1.726, p < 0.01), with the hippocampal protective effect lasting to week 14, accompanied by decreased inflammation and gliosis effect. In contrast, spike and burst suppression were achieved using an FUS regimen with 0.25-MI ISPTA 0.5 W/cm2, 30% duty cycle for 10-min sonications. This regimen reduced inflammation and gliosis at weeks 8-14 and protected hippocampal tissue. This study demonstrates that low-intensity pulsed ultrasound can modulate epileptiform activity for up to 7 weeks and, if replicated in the clinical setting, might be a practical treatment for epilepsy.

Recent Advances in the Use of Focused Ultrasound as a Treatment for Epilepsy

Epilepsy affects about 1% of the population. Approximately one third of patients with epilepsy are drug-resistant (DRE). Resective surgery is an effective treatment for DRE, yet invasive, and not all DRE patients are suitable resective surgery candidates. Focused ultrasound, a novel non-invasive neurointerventional method is currently under investigation as a treatment alternative for DRE. By emitting one or more ultrasound waves, FUS can target structures in the brain at millimeter resolution. High intensity focused ultrasound (HIFU) leads to ablation of tissue and could therefore serve as a non-invasive alternative for resective surgery. It is currently under investigation in clinical trials following the approval of HIFU for essential tremor and Parkinson’s disease. Low intensity focused ultrasound (LIFU) can modulate neuronal activity and could be used to lower cortical neuronal hyper-excitability in epilepsy patients in a non-invasive manner. The seizure-suppressive effect of LIFU has been studied in several preclinical trials, showing promising results. Further investigations are required to demonstrate translation of preclinical results to human subjects.

Feasibility of Upper Cranial Nerve Sonication in Human Application via Neuronavigated Single-Element Pulsed Focused Ultrasound

Sonicating deep brain regions with pulsed focused ultrasound using magnetic resonance imaging-guided neuronavigation single-element piezoelectric transducers is a new area of exploration for neuromodulation. Upper cranial nerves such as the trigeminal nerve and other nerves responsible for sensory/motor functions in the head may be potential targets for ultrasound pain therapy. The location of upper cranial nerves close to the skull base poses additional challenges when compared with conventional cortical or middle brain targets. In the work described here, a series of computational and empirical testing methods using human skull specimens were conducted to assess the feasibility of sonicating the trigeminal pathway near the sphenoid bone region. The results indicate a transducer with a focal length of 120 mm and diameter of 85 mm (350 kHz) can deliver sonication to upper cranial nerve regions with spatial accuracy comparable to that of focused ultrasound brain targets used in previous human studies. Temperature measurements in cortical bone and in the skull base with embedded thermocouples yield evidence of minimal bone heating. Conventional pulse parameters were found to cause reverberation interference patterns near the cranial floor; therefore, changes in pulse cycles and pulse repetition frequency were examined for reducing standing waves. Limitations and considerations for conducting ultradeep focal targeting in human applications are discussed.

Low Intensity Focused Ultrasound for Epilepsy- A New Approach to Neuromodulation

Patients with drug-resistant epilepsy (DRE) who are not surgical candidates have unacceptably few treatment options. Benefits of implanted electrostimulatory devices are still largely palliative, and many patients are not eligible to receive them. A new form of neuromodulation, low intensity focused ultrasound (LIFUS), is rapidly emerging, and has many potential intracranial applications. LIFUS can noninvasively target tissue with a spatial distribution of highly focused acoustic energy that ensures a therapeutic effect only at the geometric focus of the transducer. A growing literature over the past several decades supports the safety of LIFUS and its ability to noninvasively modulate neural tissue in animals and humans by positioning the beam over various brain regions to target motor, sensory, and visual cortices as well as frontal eye fields and even hippocampus. Several preclinical studies have demonstrated the ability of LIFUS to suppress seizures in epilepsy animal models without damaging tissue. Resection after sonication to the antero-mesial lobe showed no pathologic changes in epilepsy patients, and this is currently being trialed in serial treatments to the hippocampus in DRE. Low intensity focused ultrasound is a promising, novel, incisionless, and radiation-free alternative form of neuromodulation being investigated for epilepsy. If proven safe and effective, it could be used to target lateral cortex as well as deep structures without causing damage, and is being studied extensively to treat a wide variety of neurologic and psychiatric disorders including epilepsy.

Focused ultrasound excites action potentials in mammalian peripheral neurons in part through the mechanically gated ion channel PIEZO2

Neurons of the peripheral nervous system (PNS) are tasked with diverse roles, from encoding touch, pain, and itch to interoceptive control of inflammation and organ physiology. Thus, technologies that allow precise control of peripheral nerve activity have the potential to regulate a wide range of biological processes. Noninvasive modulation of neuronal activity is an important translational application of focused ultrasound (FUS). Recent studies have identified effective strategies to modulate brain circuits; however, reliable parameters to control the activity of the PNS are lacking. To develop robust noninvasive technologies for peripheral nerve modulation, we employed targeted FUS stimulation and electrophysiology in mouse ex vivo skin-saphenous nerve preparations to record the activity of individual mechanosensory neurons. Parameter space exploration showed that stimulating neuronal receptive fields with high-intensity, millisecond FUS pulses reliably and repeatedly evoked one-to-one action potentials in all peripheral neurons recorded. Interestingly, when neurons were classified based on neurophysiological properties, we identified a discrete range of FUS parameters capable of exciting all neuronal classes, including myelinated A fibers and unmyelinated C fibers. Peripheral neurons were excited by FUS stimulation targeted to either cutaneous receptive fields or peripheral nerves, a key finding that increases the therapeutic range of FUS-based peripheral neuromodulation. FUS elicited action potentials with millisecond latencies compared with electrical stimulation, suggesting ion channel–mediated mechanisms. Indeed, FUS thresholds were elevated in neurons lacking the mechanically gated channel PIEZO2. Together, these results demonstrate that transcutaneous FUS drives peripheral nerve activity by engaging intrinsic mechanotransduction mechanisms in neurons [B. U. Hoffman, PhD thesis, (2019)].

Spatio-Spectral Ultrasound Characterization of Reflection and Transmission Through Bone With Temperature Dependence

Transcranial focused ultrasound (tFUS) is a promising approach for the treatment of neurological disorders. It has proven useful in several clinical applications, with promising outcomes reported in the recent literature. Furthermore, it is currently being investigated in a range of neuromodulation (NM) and ablative applications, including epilepsy. In this application, tFUS access through the temporal window is the key to optimizing the treatment safety and efficacy. Traditional approaches have utilized transducers with low operating frequencies for tFUS applications. Modern array transducers and driving systems allow for more intelligent use of the temporal window by exploiting the spatio-spectral transmission bandwidth to a specified target or targets within the brain. To demonstrate the feasibility of this approach, we have investigated the ultrasound reflection and transmission characteristics for different access points within the temporal window of human skull samples ex vivo. Different transmit-receive (Rx) configurations are used for characterization of the spatio-spectral variability in reflection and transmission through the temporal window. In this article, we show results from a dual-piston transducer set up in the frequency range of 2-7 MHz. Broadband pulses as well as synthesized orthogonal frequency division multiplexed (OFDM) waveforms were used. The latter was used to improve the magnitude and phase measurements in 100-kHz subbands within the 2-7 MHz spectral window. A temperature-controlled water bath was used to characterize the change in reflection and transmission characteristics with temperature in the 25°C-43°C range. The measured values of the complex reflection and transmission coefficients exhibited significant variations with space, frequency, and temperature. On the other hand, the measured transmission phase varied more with location and frequency, with smaller sensitivity to temperature. A measurement-based hybrid angular spectrum (HAS) simulation through the human temporal bone was used to demonstrate the dependence of focusing gain on the skull profile and spatial distribution of change of speed of sound (SOS) at different skull temperatures.

Enhancement of functional corticomuscular coupling after transcranial ultrasound stimulation in mice

OBJECTIVE

Transcranial ultrasound stimulation (TUS), a large penetration depth and high spatial resolution technology, has developed rapidly in recent years. This study aimed to explore and evaluate the neuromodulation effects of TUS on mouse motor neural circuits under different parameters.

APPROACH

Our study used functional corticomuscular coupling (FCMC) as an index to explore the modulation mechanism for movement control under different TUS parameters (intensity [Isppa] and stimulation duration [SD]). We collected local field potential (LFP) and tail electromyographic (EMG) data under TUS in healthy mice and then introduced the time-frequency coherence method to analyze the FCMC before and after TUS in the time-frequency domain. After that, we defined the relative coherence area (RCA) to quantify the coherence between LFP and EMG under TUS.

MAIN RESULTS

The FCMC at theta, alpha, beta, and gamma bands was enhanced after TUS, and the neuromodulation efficacy mainly occurred in the lower frequency band (theta and alpha band). After TUS with different parameters, the FCMC in all selected frequency bands showed a tendency of increasing first and then decreasing. Further analysis showed that the maximum coupling value of theta band appeared from 0.2 to 0.4 s, and that the maximum coupling value in alpha and gamma band appeared from 0 to 0.2 s.

SIGNIFICANCE

The aforementioned results demonstrate that FCMC in the motor cortex could be modulated by TUS. We provide a theoretical basis for further exploring the modulation mechanism of TUS parameters and clinical application.

Neuronal responses to focused ultrasound are gated by pre-stimulation brain rhythms

BACKGROUND

Owing to its high spatial resolution and penetration depth, transcranial focused ultrasound stimulation (tFUS) is one of the most promising approaches to non-invasive neuromodulation. Identifying the impact of endogenous neural activity on neuromodulation outcome is critical to harnessing the potential of tFUS.

OBJECTIVE

Here we sought to identify the relationship between pre-stimulation neural activity and the neuronal response to tFUS.

METHODS

We applied 3 min of continuous-wave tFUS to the hippocampal region of the rat while recording local field potentials (LFP) and multi-unit activity (MUA) from the target. We also tested the application of tFUS but with an air gap separating the transducer and the skull, as well as active stimulation of the contralateral olfactory bulb.

RESULTS

We observed a modest but significant increase in firing rate during hippocampal tFUS, but not during stimulation of the olfactory bulb or when an air gap was present. Importantly, the observed firing rate increase was significantly modulated by the power of baseline oscillations in the LFP, with low levels of delta (1-3 Hz) and high levels of theta (4-10 Hz) and gamma (30-250 Hz) power producing significantly larger firing rate increases. Firing rate increases were also amplified by a factor of 7× when stimulation was applied during periods of frequent sharp-wave ripple (SWR) activity.

CONCLUSION

Our findings suggest that baseline brain rhythms may effectively "gate" the response to tFUS.

Surgery procedures in temporal lobe epilepsies

Temporal lobe epilepsy (TLE) is the most common cause of refractory epilepsy amenable for surgical treatment and seizure control. Surgery for TLE is a safe and effective strategy. The seizure-free rate after surgical resection in patients with mesial or neocortical TLE is about 70%. Resective surgery has an advantage over stereotactic radiosurgery in terms of seizure outcomes for mesial TLE patients. Both techniques have similar results for safety, cognitive outcomes, and associated costs. Stereotactic radiosurgery should therefore be seen as an alternative to open surgery for patients with contraindications for or with reluctance to undergo open surgery. Laser interstitial thermal therapy (LITT) has also shown promising results as a curative technique in mesial TLE but needs to be more deeply evaluated. Brain-responsive stimulation represents a palliative treatment option for patients with unilateral or bilateral MTLE who are not candidates for temporal lobectomy or who have failed a prior mesial temporal lobe resection. Overall, despite the expansion of innovative techniques in recent years, resective surgery remains the reference treatment for TLE and should be proposed as the first-line surgical modality. In the future, ultrasound therapies could become a credible therapeutic option for refractory TLE patients.