Non-invasive transcranial ultrasound stimulation for neuromodulation

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Safety and efficacy of repetitive stimulation of the left dorsolateral prefrontal cortex using transcranial focused ultrasound in treatment-resistant depressed patients: A non-inferiority randomized controlled trial protocol

BACKGROUND

About 30% of patients diagnosed with major depressive disorder fail with the mainstream pharmacological treatment. Patients who do not achieve clinical remission of symptoms, even with two different antidepressants, are classified with treatment-resistant depression (TDR). This condition imposes an additional burden with increased Disability Adjusted Life Years. Therefore, complementary treatments, such as neuromodulation, are necessary. The transcranial focused ultrasound (tFUS) has emerged in the past few years as a reliable method for non-invasive neuromodulation in humans and may help treat TRD. This study aims to propose a research protocol for a non-inferiority randomized clinical trial of TDR with tFUS.

METHODS

Patients with documented TRD will be screened upon entering the TRD outpatient clinic at UFMG (Brazil). One hundred patients without a clinical history of other psychiatric illness, anatomical abnormalities on magnetic resonance imaging (MRI), or treatment with electroconvulsive therapy will be invited to participate. Patients will be randomized (1:1) into two groups: 1) treatment with a previously established protocol of transcranial magnetic stimulation; and 2) treatment with a similar protocol using the stimulation. Besides regular consultations in the outpatient clinic, both groups will attend 7 protocolled spaced days of brain stimulation targeted at the left dorsolateral prefrontal cortex. They will also be submitted to 4 sessions of image studies (2 MRIs, 2 positron-emission tomography), 3 of neuropsychological assessments (at baseline, 1 week and 2 months after treatment), the Montgomery-Åsberg Depression Rating Scale to analyze the severity of depressive symptoms.

DISCUSSION

This clinical trial intends to verify the safety and clinical efficacy of tFUS stimulation of the dorsolateral prefrontal cortex of patients with TRD, compared with a previously established neuromodulation method.

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

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

Recent advances of ultrasound-responsive nanosystems in tumor immunotherapy

Immunotherapy has revolutionized cancer treatment by boosting the immune system and preventing disease escape mechanisms. Despite its potential, challenges like limited response rates and adverse immune effects impede its widespread clinical adoption. Ultrasound (US), known for its safety and effectiveness in tumor diagnosis and therapy, has been shown to significantly enhance immunotherapy when used with nanosystems. High-intensity focused ultrasound (HIFU) can obliterate tumor cells and elicit immune reactions through the creation of immunogenic debris. Low-intensity focused ultrasound (LIFU) bolsters tumor immunosuppression and mitigates metastasis risk by concentrating dendritic cells. Ultrasonic cavitation (UC) produces microbubbles that can transport immune enhancers directly, thus strengthening the immune response and therapeutic impact. Sonodynamic therapy (SDT) merges nanotechnology with immunotherapy, using specialized sonosensitizers to kill cancer cells and stimulate immune responses, increasing treatment success. This review discusses the integration of ultrasound-responsive nanosystems in tumor immunotherapy, exploring future opportunities and current hurdles.

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

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

Towards an ion-channel-centric approach to ultrasound neuromodulation

Ultrasound neuromodulation is a promising technology that could revolutionize study and treatment of brain conditions ranging from mood disorders to Alzheimer's disease and stroke. An understanding of how ultrasound directly modulates specific ion channels could provide a roadmap for targeting specific neurological circuits and achieving desired neurophysiological outcomes. Although experimental challenges make it difficult to unambiguously identify which ion channels are sensitive to ultrasound in vivo, recent progress indicates that there are likely several different ion channels involved, including members of the K2P, Piezo, and TRP channel families. A recent result linking TRPM2 channels in the hypothalamus to induction of torpor by ultrasound in rodents demonstrates the feasibility of targeting a specific ion channel in a specific population of neurons.

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

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

Application of Data-Driven computing to patient-specific prediction of the viscoelastic response of human brain under transcranial ultrasound stimulation

We present a class of model-free Data-Driven solvers that effectively enable the utilization of in situ and in vivo imaging data directly in full-scale calculations of the mechanical response of the human brain to sonic and ultrasonic stimulation, entirely bypassing the need for analytical modeling or regression of the data. The well-posedness of the approach and its convergence with respect to data are proven analytically. We demonstrate the approach, including its ability to make detailed spatially resolved patient-specific predictions of wave patterns, using public-domain MRI images, MRE data and commercially available solid-mechanics software.

Low-intensity focused ultrasound to the human insular cortex differentially modulates the heartbeat-evoked potential: a proof-of-concept study

Background

The heartbeat evoked potential (HEP) is a brain response time-locked to the heartbeat and a potential marker of interoceptive processing. The insula and dorsal anterior cingulate cortex (dACC) are brain regions that may be involved in generating the HEP. Low-intensity focused ultrasound (LIFU) is a non-invasive neuromodulation technique that can selectively target sub-regions of the insula and dACC to better understand their contributions to the HEP.

Objective

Proof-of-concept study to determine whether LIFU modulation of the anterior insula (AI), posterior insula (PI), and dACC influences the HEP.

Methods

In a within-subject, repeated-measures design, healthy human participants (n=16) received 10 minutes of stereotaxically targeted LIFU to the AI, PI, dACC or Sham at rest during continuous electroencephalography (EEG) and electrocardiography (ECG) recording on separate days. Primary outcome was change in HEP amplitudes. Relationships between LIFU pressure and HEP changes were examined using linear mixed modelling. Peripheral indices of visceromotor output including heart rate and heart rate variability (HRV) were explored between conditions.

Results

Relative to sham, LIFU to the PI, but not AI or dACC, decreased HEP amplitudes; this was partially explained by increased LIFU pressure. LIFU did not affect time or frequency dependent measures of HRV.

Conclusions

These results demonstrate the ability to modulate HEP amplitudes via non-invasive targeting of key interoceptive brain regions. Our findings have implications for the causal role of these areas in bottom-up heart-brain communication that could guide future work investigating the HEP as a marker of interoceptive processing in healthy and clinical populations.

The mechanistic divide in psychedelic neuroscience: An unbridgeable gap?

In recent years, psychedelics have generated considerable excitement and interest as potential novel therapeutics for an array of conditions, with the most advanced evidence base in the treatment of certain severe and/or treatment-resistant psychiatric disorders. An array of clinical and pre-clinical evidence has informed our current understanding of how psychedelics produce profound alterations in consciousness. Mechanisms of psychedelic action include receptor binding and downstream cellular and transcriptional pathways, with long-term impacts on brain structure and function-from the level of single neurons to large-scale circuits. In this perspective, we first briefly review and synthesize separate lines of research on potential mechanistic processes underlying the acute and long-term effects of psychedelic compounds, with a particular emphasis on highlighting current theoretical models of psychedelic drug action and their relationships to therapeutic benefits for psychiatric and brain-based disorders. We then highlight an existing area of ongoing controversy we argue is directly informed by theoretical models originating from disparate levels of inquiry, and we ultimately converge on the notion that bridging the current chasm in explanatory models of psychedelic drug action across levels of inquiry (molecular, cellular, circuit, and psychological/behavioral) through innovative methods and collaborative efforts will ultimately yield the comprehensive understanding needed to fully capitalize on the potential therapeutic properties of these compounds.

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.

Personalized depth-specific neuromodulation of the human primary motor cortex via ultrasound

Non-invasive brain stimulation has the potential to boost neuronal plasticity in the primary motor cortex (M1), but it remains unclear whether the stimulation of both superficial and deep layers of the human motor cortex can effectively promote M1 plasticity. Here, we leveraged transcranial ultrasound stimulation (TUS) to precisely target M1 circuits at depths of approximately 5 mm and 16 mm from the cortical surface. Initially, we generated computed tomography images from each participant's individual anatomical magnetic resonance images (MRI), which allowed for the generation of accurate acoustic simulations. This process ensured that personalized TUS was administered exactly to the targeted depths within M1 for each participant. Using long-term depression and long-term potentiation (LTD/LTP) theta-burst stimulation paradigms, we examined whether TUS over distinct depths of M1 could induce LTD/LTP plasticity. Our findings indicated that continuous theta-burst TUS-induced LTD-like plasticity with both superficial and deep M1 stimulation, persisting for at least 30 min. In comparison, sham TUS did not significantly alter M1 excitability. Moreover, intermittent theta-burst TUS did not result in the induction of LTP- or LTD-like plasticity with either superficial or deep M1 stimulation. These findings suggest that the induction of M1 plasticity can be achieved with ultrasound stimulation targeting distinct depths of M1, which is contingent on the characteristics of TUS. KEY POINTS: The study integrated personalized transcranial ultrasound stimulation (TUS) with electrophysiology to determine whether TUS targeting superficial and deep layers of the human motor cortex (M1) could elicit long-term depression (LTD) or long-term potentiation (LTP) plastic changes. Utilizing acoustic simulations derived from individualized pseudo-computed tomography scans, we ensured the precision of TUS delivery to the intended M1 depths for each participant. Continuous theta-burst TUS targeting both the superficial and deep layers of M1 resulted in the emergence of LTD-like plasticity, lasting for at least 30 min. Administering intermittent theta-burst TUS to both the superficial and deep layers of M1 did not lead to the induction of LTP- or LTD-like plastic changes. We suggest that theta-burst TUS targeting distinct depths of M1 can induce plasticity, but this effect is dependent on specific TUS parameters.

Label free, capillary-scale blood flow mapping in vivo reveals that low intensity focused ultrasound evokes persistent dilation in cortical microvasculature

Non-invasive, low intensity focused ultrasound (FUS) is an emerging neuromodulation technique that offers the potential for precision, personalized therapy. An increasing body of research has identified mechanosensitive ion channels that can be modulated by FUS and support acute electrical activity in neurons. However, neuromodulatory effects that persist from hours to days have also been reported. The brain's ability to provide targeted blood flow to electrically active regions involve a multitude of non-neuronal cell types and signaling pathways in the cerebral vasculature; an open question is whether persistent effects can be attributed, at least partly, to vascular mechanisms. Using a novel in vivo optical approach, we found that microvascular responses, unlike larger vessels which prior investigations have explored, exhibit persistent dilation. This finding and approach offers a heretofore unseen aspect of the effects of FUS in vivo and indicate that concurrent changes in neurovascular function may partially underly persistent neuromodulatory effects.

Noninvasive neuromodulation of subregions of the human insula differentially affect pain processing and heart-rate variability: a within-subjects pseudo-randomized trial

ABSTRACT

The insula is an intriguing target for pain modulation. Unfortunately, it lies deep to the cortex making spatially specific noninvasive access difficult. Here, we leverage the high spatial resolution and deep penetration depth of low-intensity focused ultrasound (LIFU) to nonsurgically modulate the anterior insula (AI) or posterior insula (PI) in humans for effect on subjective pain ratings, electroencephalographic (EEG) contact heat-evoked potentials, as well as autonomic measures including heart-rate variability (HRV). In a within-subjects, repeated-measures, pseudo-randomized trial design, 23 healthy volunteers received brief noxious heat pain stimuli to the dorsum of their right hand during continuous heart-rate, electrodermal, electrocardiography and EEG recording. Low-intensity focused ultrasound was delivered to the AI (anterior short gyrus), PI (posterior longus gyrus), or under an inert Sham condition. The primary outcome measure was pain rating. Low-intensity focused ultrasound to both AI and PI similarly reduced pain ratings but had differential effects on EEG activity. Low-intensity focused ultrasound to PI affected earlier EEG amplitudes, whereas LIFU to AI affected later EEG amplitudes. Only LIFU to the AI affected HRV as indexed by an increase in SD of N-N intervals and mean HRV low-frequency power. Taken together, LIFU is an effective noninvasive method to individually target subregions of the insula in humans for site-specific effects on brain biomarkers of pain processing and autonomic reactivity that translates to reduced perceived pain to a transient heat stimulus.

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.

Stability of steady-state visual evoked potential contrast response functions

Repetitive sensory stimulation has been shown to induce neuroplasticity in sensory cortical circuits, at least under certain conditions. We measured the plasticity-inducing effect of repetitive contrast-reversal-sweep steady-state visual-evoked potential (ssVEP) stimuli, hoping to employ the ssVEP's high signal-to-noise electrophysiological readout in the study of human visual cortical neuroplasticity. Steady-state VEP contrast-sweep responses were measured daily for 4 days (four 20-trial blocks per day, 20 participants). No significant neuroplastic changes in response amplitude were observed either across blocks or across days. Furthermore, response amplitudes were stable within-participant, with measured across-block and across-day coefficients of variation (CV = SD/mean) of 15-20 ± 2% and 22-25 ± 2%, respectively. Steady-state VEP response phase was also highly stable, suggesting that temporal processing delays in the visual system vary by at most 2-3 ms across blocks and days. While we fail to replicate visual stimulation-dependent cortical plasticity, we show that contrast-sweep steady-state VEPs provide a stable human neurophysiological measure well suited for repeated-measures longitudinal studies.

Evaluation of advective solute infiltration into porous media by pulsed focused ultrasound-induced acoustic streaming effects

PURPOSE

Acoustic streaming induced by applying transcranial focused ultrasound (FUS) promotes localized advective solute transport in the brain and has recently garnered research interest for drug delivery and enhancement of brain waste clearance. The acoustic streaming behavior in brain tissue is difficult to model numerically and thus warrants an in vitro examination of the effects of using different sonication parameters, in terms of frequency, intensity, and pulse duration (PD).

METHODS

Melamine and polyvinyl alcohol (PVA) foams were used to mimic the porous brain tissue, which contains leptomeningeal fenestrations and perivascular space, while agar hydrogel was used to emulate denser neuropil. FUS was delivered to these media, which were immersed in a phosphate-buffered saline containing toluidine blue O dye, across various frequencies (400, 500, and 600 kHz; applicable to transcranial delivery) in a pulsed mode at two different spatialpeak pulse-average intensities (3 and 4 W/cm2).

RESULTS

Image analysis showed that the use of 400 kHz yielded the greatest dye infiltration in melamine foam, while sonication had no impact on infiltration in the agar hydrogel due to the dominance of diffusional transport. Using a fixed spatial-peak temporal-average intensity of 0.4 W/cm2 at 400 kHz, a PD of 75 ms resulted in the greatest infiltration depth in both melamine and PVA foams among the tested range (50-150 ms).

CONCLUSION

These findings suggest the existence of a specific frequency and PD that induce greater enhancement of solute/fluid movement, which may contribute to eventual in vivo applications in promoting waste clearance from the brain.

Pre-clinical indications of brain stimulation treatments for non-affective psychiatric disorders, a status update

Over the past two decades noninvasive brain stimulation (NIBS) techniques have emerged as powerful therapeutic options for a range of psychiatric and neurological disorders. NIBS are hypothesized to rebalance pathological brain networks thus reducing symptoms and improving functioning. This development has been fueled by controlled studies with increasing size and rigor aiming to characterize how treatments induce clinically effective change. Clinical trials of NIBS for specific indications have resulted in federal approval for unipolar depression, bipolar depression, smoking cessation, and obsessive-compulsive disorder in the United States, and several other indications worldwide. As a rapidly emerging field, there are numerous pre-clinical indications currently in development using a variety of electrical and magnetic, non-convulsive, and convulsive approaches. This review discusses the state-of-the-science surrounding promising avenues of NIBS currently in pre-approval stages for non-affective psychiatric disorders. We consider emerging therapies for psychosis, anxiety disorders, obsessive-compulsive disorder, and borderline personality disorder, utilizing transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and magnetic seizure therapy (MST), with an additional brief section for early-stage techniques including transcranial focused ultrasound stimulation (tFUS) and transcranial alternating current stimulation (tACS). As revealed in this review, there is considerable promise across all four psychiatric indications with different NIBS approaches. Positive findings are notable for the treatment of psychosis using tDCS, MST, and rTMS. While rTMS is already FDA approved for the treatment of obsessive-compulsive disorder, methodologies such as tDCS also demonstrate potential in this condition. Emerging techniques show promise for treating non-affective disorders likely leading to future regulatory approvals.

Accelerated Transcranial Ultrasound Neuromodulation in Parkinson's Disease: A Pilot Study

OBJECTIVE

Low-intensity transcranial focused ultrasound (TUS) is a novel method for neuromodulation. We aimed to study the feasibility of stimulating the bilateral primary motor cortices (M1) with accelerated theta-burst TUS (a-tbTUS) on neurophysiologic and clinical outcomes in Parkinson's disease (PD).

METHODS

Patients were randomly assigned to receive active or sham a-tbTUS for the first visit and the alternate condition on the second visit, at least 10 days apart. a-tbTUS was administered in three consecutive sonications at 30-minute intervals. We used an accelerated protocol to produce an additive effect of stimulation. Patients were studied in the OFF-medication state. Transcranial magnetic stimulation (TMS)-elicited motor-evoked potentials (MEPs) were used to assess motor cortical excitability before and after TUS. Clinical outcomes after a-tbTUS administration were assessed using the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS)-III.

RESULTS

A total of 20 visits were conducted in 10 PD patients. Compared to the baseline, TMS-elicited MEP amplitudes significantly increased following active but not sham sonication (P = 0.0057). MEP amplitudes were also higher following a-tbTUS than sham sonication (P = 0.0064). There were no statistically significant changes in MDS-UPDRS-III scores with active or sham a-tbTUS.

CONCLUSIONS

a-tbTUS increases motor cortex excitability and is a feasible non-invasive neuromodulation strategy in PD. Future studies should determine optimal dosing parameters and the durability of neurophysiologic and clinical outcomes in PD patients. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Transcranial ultrasound neuromodulation facilitates isoflurane-induced general anesthesia recovery and improves cognition in mice

Delayed arousal and cognitive dysfunction are common, especially in older patients after general anesthesia (GA). Elevating central nervous system serotonin (5-HT) levels can promote recovery from GA and increase synaptic plasticity to improve cognition. Ultrasound neuromodulation has become a noninvasive physical intervention therapy with high spatial resolution and penetration depth, which can modulate neuronal excitability to treat psychiatric and neurodegenerative diseases. This study aims to use ultrasound to noninvasively modulate the brain 5-HT levels of mice to promote recovery from GA and improve cognition in mice. The dorsal raphe nucleus (DRN) of mice during GA was stimulated by the 1.1 MHz ultrasound with a negative pressure of 356 kPa, and the liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) method was used to measure the DRN 5-HT concentrations. The mice's recovery time from GA was assessed, and the cognition was evaluated through spontaneous alternation Y-maze and novel object recognition (NOR) tests. After ultrasound stimulation, the mice's DRN 5-HT levels were significantly increased (control: 554.0 ± 103.2 ng/g, anesthesia + US: 664.2 ± 84.1 ng/g, *p = 0.0389); the GA recovery time (return of the righting reflex (RORR) emergence latency time) of mice was significantly reduced (anesthesia: 331.6 ± 70 s, anesthesia + US: 223.2 ± 67.7 s, *p = 0.0215); the spontaneous rotation behavior score of mice was significantly increased (anesthesia: 59.46 ± 5.26 %, anesthesia + US: 68.55 ± 5.24 %; *p = 0.0126); the recognition index was significantly increased (anesthesia: 55.02 ± 6.23 %, anesthesia + US: 78.52 ± 12.21 %; ***p = 0.0009). This study indicates that ultrasound stimulation of DRN increases serotonin levels, accelerates recovery from anesthesia, and improves cognition, which could be an important strategy for treating delayed arousal, postoperative delirium, or even lasting cognitive dysfunction after GA.

Enhanced and spatially controllable neuronal activity induced by transcranial focused ultrasound stimulation combined with phase-change nanodroplets

Non-invasive ultrasound neuromodulation (USNM) is a powerful tool to explore neural circuits and treat neurological disorders. Due to the heterogeneity of the skull and regional variations in modulation and treatment objectives, it is necessary to develop an efficient and spatially controllable neuromodulation approach. Recently, transcranial focused ultrasound (tFUS) combined with external biomicro/nanomaterials for brain stimulation has garnered significant attention. This study focused on tFUS combined with perfluoropentane (PFP) nanodroplets (NDs) to improve the efficacy and spatial controllability of USNM. The developed two-stage variable pulse tFUS sequence that include the acoustic droplet vaporization (ADV) pulse for vaporizing PFP NDs into microbubbles (MBs) and the USNM sequence for inducing mechanical oscillations of the formed MBs to enhance neuronal activity. Further, adjusting the acoustic pressure of the ADV pulse generated the controllable vaporization regions, thereby achieving spatially controllable neuromodulation. The results showed that the mean densities of c-fos+ cells expression in the group of PFP NDs with ADV (109 ± 19 cells/mm2) were significantly higher compared to the group without ADV (37.34 ± 8.24 cells/mm2). The acoustic pressure of the ADV pulse with 1.98 MPa and 2.81 MPa in vitro generated the vaporization regions of 0.146 ± 0.032 cm2 and 0.349 ± 0.056 cm2, respectively. Under the same stimulation conditions, a larger vaporization region was also obtained with higher acoustic pressure in vivo, inducing a broader region of neuronal activation. Therefore, this study will serve as a valuable reference for developing the efficient and spatially controllable tFUS neuromodulation strategy.

Modeling ultrasound modulation of neural function in a single cell

Background

Low intensity ultrasound stimulation has been shown to non-invasively modulate neural function in the central nervous system (CNS) and peripheral nervous system (PNS) with high precision. Ultrasound sonication is capable of either excitation or inhibition, depending on the ultrasound parameters used. On the other hand, the mode of interaction of ultrasonic waves with the neural tissue for effective neuromodulation remains ambiguous.

New method

Here within we propose a numerical model that incorporates the mechanical effects of ultrasound stimulation on the Hodgkin-Huxley (HH) neuron by incorporating the relation between increased external pressure and the membrane induced tension, with a stress on the flexoelectric effect on the neural membrane. The external pressure causes an increase in the total tension of the membrane thus affecting the probability of the ion channels being open after the conformational changes that those channels undergo.

Results

The interplay between varying the acoustic intensities and frequencies depicts different action potential suppression rates, whereby a combination of low intensity and low frequency ultrasound sonication proved to be the most effective in modulating neural function.Comparison with Existing Methods: Our method solely depends on the HH model of a single neuron and the linear flexoelectric effect of the dielectric neural membrane, when under an ultrasound-induced mechanical strain, while varying the ion-channels conductances based on different sonication frequencies and intensities. We study the effect of ultrasound parameters on the firing rate, latency, and action potential amplitude of a HH neuron for a better understanding of the neuromodulation modality of ultrasound stimulation (in the continuous and pulsed modes).

Conclusions

This simulation work confirms the published experimental data that low intensity and low frequency ultrasound sonication has a higher success rate of modulating neural firing.

Thalamo-cortical circuits associated with trait- and state-repetitive negative thinking in major depressive disorder

BACKGROUND

Repetitive negative thinking (RNT), often referred to as rumination in the mood disorders literature, is a symptom dimension associated with poor prognosis and suicide in major depressive disorder (MDD). Given the transdiagnostic nature of RNT, this study aimed to evaluate the hypothesis that neurobiological substrates of RNT in MDD may share the brain mechanisms underlying obsessions, particularly those involving cortico-striatal-thalamic-cortical (CSTC) circuits.

METHODS

Thirty-nine individuals with MDD underwent RNT induction during fMRI. Trait-RNT was measured by the Ruminative Response Scale (RRS) and state-RNT was measured by a visual analogue scale. We employed a connectome-wide association analysis examining the association between RNT intensity with striatal and thalamic connectivity.

RESULTS

A greater RRS score was associated with hyperconnectivity of the right mediodorsal thalamus with prefrontal cortex, including lateral orbitofrontal cortex, along with Wernicke's area and posterior default mode network nodes (t = 4.66-6.70). A greater state-RNT score was associated with hyperconnectivity of the right laterodorsal thalamus with bilateral primary sensory and motor cortices, supplementary motor area, and Broca's area (t = 4.51-6.57). Unexpectedly, there were no significant findings related to the striatum.

CONCLUSIONS

The present results suggest RNT in MDD is subserved by abnormal connectivity between right thalamic nuclei and cortical regions involved in both visceral and higher order cognitive processing. Emerging deep-brain neuromodulation methods may be useful to establish causal relationships between dysfunction of right thalamic-cortical circuits and RNT in MDD.

Role of medial prefrontal cortex and primary somatosensory cortex in self and other-directed vicarious social touch: a TMS study

Conflicting evidence points to the contribution of several key nodes of the 'social brain' to the processing of both discriminatory and affective qualities of interpersonal touch. Whether the primary somatosensory cortex (S1) and the medial prefrontal cortex (mPFC), two brain areas vital for tactile mirroring and affective mentalizing, play a functional role in shared representations of C-tactile (CT) targeted affective touch is still a matter of debate. Here, we used offline continuous theta-burst transcranial magnetic stimulation (cTBS) to mPFC, S1 and vertex (control) prior to participants providing ratings of vicarious touch pleasantness for self and others delivered across several body sites at CT-targeted velocities. We found that S1-cTBS led to a significant increase in touch ratings to the self, with this effect being positively associated to levels of interoceptive awareness. Conversely, mPFC-cTBS reduced pleasantness ratings for touch to another person. These effects were not specific for CT-optimal (slow) stroking velocities, but rather they applied to all types of social touch. Overall, our findings challenge the causal role of the S1 and mPFC in vicarious affective touch and suggest that self- vs other-directed vicarious touch responses might crucially depend on the specific involvement of key social networks in gentle tactile interactions.

Ultrasound-Sensitive Intelligent Nanosystems: A Promising Strategy for the Treatment of Neurological Diseases

Neurological diseases are a major global health challenge, affecting hundreds of millions of people worldwide. Ultrasound therapy plays an irreplaceable role in the treatment of neurological diseases due to its noninvasive, highly focused, and strong tissue penetration capabilities. However, the complexity of brain and nervous system and the safety risks associated with prolonged exposure to ultrasound therapy severely limit the applicability of ultrasound therapy. Ultrasound-sensitive intelligent nanosystems (USINs) are a novel therapeutic strategy for neurological diseases that bring greater spatiotemporal controllability and improve safety to overcome these challenges. This review provides a detailed overview of therapeutic strategies and clinical advances of ultrasound in neurological diseases, focusing on the potential of USINs-based ultrasound in the treatment of neurological diseases. Based on the physical and chemical effects induced by ultrasound, rational design of USINs is a prerequisite for improving the efficacy of ultrasound therapy. Recent developments of ultrasound-sensitive nanocarriers and nanoagents are systemically reviewed. Finally, the challenges and developing prospects of USINs are discussed in depth, with a view to providing useful insights and guidance for efficient ultrasound treatment of neurological diseases.

Desynchronization of neuronal firing in multiparameter ultrasound stimulation

Low-intensity transcranial ultrasound stimulation, a novel neuromodulation technique, that possesses the advantages of non-invasiveness, high penetration depth, and high spatial resolution, has achieved positive neuromodulation effects in animal studies. But the regulatory mechanism remains controversial. The intramembrane cavitation effect is considered one of the mechanisms for ultrasound neuromodulation. In this study, the modified equations of ultrasonic cavitation bubble dynamics were coupled with the dual-coupled neuron Hindmarsh-Rose model, small-world neural network model, and the Jansen-Rit neural mass model, which simulate simple coupled neurons, complex neuronal networks, and discharge signals in epileptic disorders respectively. The results demonstrated that ultrasound stimulation has an appreciable modulatory effect on neuronal firing desynchronization in Hindmarsh-Rose model and small-world neural network model. The desynchronization effect is related to the stimulation frequency and intensity. Furthermore, ultrasound stimulation has an inhibitory effect on epileptic seizures, and the effect is enhanced by increasing ultrasound frequency from 0.1-1.0 MHz. This is the first combination of ultrasonic intramembrane cavitation effect theory with neurons and neural network firing desynchronization, which can provide guidance of parametric and theories support for the studies of neurological diseases such as epilepsy and Parkinson's disease.

Functional material-mediated wireless physical stimulation for neuro-modulation and regeneration

Nerve injuries and neurological diseases remain intractable clinical challenges. Despite the advantages of stem cell therapy in treating neurological disorders, uncontrollable cell fates and loss of cell function in vivo are still challenging. Recently, increasing attention has been given to the roles of external physical signals, such as electricity and ultrasound, in regulating stem cell fate as well as activating or inhibiting neuronal activity, which provides new insights for the treatment of neurological disorders. However, direct physical stimulations in vivo are short in accuracy and safety. Functional materials that can absorb energy from a specific physical field exerted in a wireless way and then release another localized physical signal hold great advantages in mediating noninvasive or minimally invasive accurate indirect physical stimulations to promote the therapeutic effect on neurological disorders. In this review, the mechanism by which various physical signals regulate stem cell fate and neuronal activity is summarized. Based on these concepts, the approaches of using functional materials to mediate indirect wireless physical stimulation for neuro-modulation and regeneration are systematically reviewed. We expect that this review will contribute to developing wireless platforms for neural stimulation as an assistance for the treatment of neurological diseases and injuries.

A Bibliometric Analysis for Low-Intensity Ultrasound Study Over the Past Three Decades

Low-intensity ultrasound (LI-US) is a non-invasive stimulation technique that has emerged in recent years and has been shown to have positive effects on neuromodulation, fracture healing, inflammation improvement, and metabolic regulation. This study reports the conclusions of a bibliometric analysis of LI-US. Input data for the period between 1995 and 2022, including 7209 related articles in the field of LI-US, were collected from the core library of the Web of Science (WOS) database. Using these data, a set of bibliometric indicators was obtained to gain knowledge on different aspects: global production, research areas, and sources analysis, contributions of countries and institutions, author analysis, citation analysis, and keyword analysis. This study combined the data analysis capabilities provided by the WOS database, making use of two bibliometric software tools: R software and VOS viewer to achieve analysis and data exploration visualization, and predicted the further development trends of LI-US. It turns out that the United States and China are co-leaders while Zhang ZG is the most significant author in LI-US. In the future, the hot spots of LI-US will continue to focus on parameter research, mechanism discussion, safety regulations, and neuromodulation applications.

Generating Patient-Specific Acoustic Simulations for Transcranial Focused Ultrasound Procedures Based on Optical Tracking Information

Optical tracking is a real-time transducer positioning method for transcranial focused ultrasound (tFUS) procedures, but the predicted focus from optical tracking typically does not incorporate subject-specific skull information. Acoustic simulations can estimate the pressure field when propagating through the cranium but rely on accurately replicating the positioning of the transducer and skull in a simulated space. Here, we develop and characterize the accuracy of a workflow that creates simulation grids based on optical tracking information in a neuronavigated phantom with and without transmission through an ex vivo skull cap. The software pipeline could replicate the geometry of the tFUS procedure within the limits of the optical tracking system (transcranial target registration error (TRE): 3.9 ± 0.7 mm). The simulated focus and the free-field focus predicted by optical tracking had low Euclidean distance errors of 0.5±0.1 and 1.2±0.4 mm for phantom and skull cap, respectively, and some skull-specific effects were captured by the simulation. However, the TRE of simulation informed by optical tracking was 4.6±0.2, which is as large or greater than the focal spot size used by many tFUS systems. By updating the position of the transducer using the original TRE offset, we reduced the simulated TRE to 1.1 ± 0.4 mm. Our study describes a software pipeline for treatment planning, evaluates its accuracy, and demonstrates an approach using MR-acoustic radiation force imaging as a method to improve dosimetry. Overall, our software pipeline helps estimate acoustic exposure, and our study highlights the need for image feedback to increase the accuracy of tFUS dosimetry.

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

Introduction

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

Methods

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

Results

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

Discussion

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

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

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

Transcranial focused ultrasound-mediated neurochemical and functional connectivity changes in deep cortical regions in humans

Low-intensity transcranial ultrasound stimulation (TUS) is an emerging non-invasive technique for focally modulating human brain function. The mechanisms and neurochemical substrates underlying TUS neuromodulation in humans and how these relate to excitation and inhibition are still poorly understood. In 24 healthy controls, we separately stimulated two deep cortical regions and investigated the effects of theta-burst TUS, a protocol shown to increase corticospinal excitability, on the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and functional connectivity. We show that theta-burst TUS in humans selectively reduces GABA levels in the posterior cingulate, but not the dorsal anterior cingulate cortex. Functional connectivity increased following TUS in both regions. Our findings suggest that TUS changes overall excitability by reducing GABAergic inhibition and that changes in TUS-mediated neuroplasticity last at least 50 mins after stimulation. The difference in TUS effects on the posterior and anterior cingulate could suggest state- or location-dependency of the TUS effect-both mechanisms increasingly recognized to influence the brain's response to neuromodulation.

Functional role of the theory of mind network in integrating mentalistic prior information with action kinematics during action observation

Inferring intentions from verbal and nonverbal human behaviour is critical for everyday social life. Here, we combined Transcranial Magnetic Stimulation (TMS) with a behavioural priming paradigm to test whether key nodes of the Theory of Mind network (ToMn) contribute to understanding others' intentions by integrating prior knowledge about an agent with the observed action kinematics. We used a modified version of the Faked-Action Discrimination Task (FAD), a forced-choice paradigm in which participants watch videos of actors lifting a cube and judge whether the actors are trying to deceive them concerning the weight of the cube. Videos could be preceded or not by verbal description (prior) about the agent's truthful or deceitful intent. We applied single pulse TMS over three key nodes of the ToMn, namely dorsomedial prefrontal cortex (dmPFC), right posterior superior temporal sulcus (pSTS) and right temporo-parietal junction (rTPJ). Sham-TMS served as a control (baseline) condition. Following sham or rTPJ stimulation, we observed no consistent influence of priors on FAD performance. In contrast, following dmPFC stimulation, and to a lesser extent pSTS stimulation, truthful and deceitful actions were perceived as more deceptive only when the prior suggested a dishonest intention. These findings highlight a functional role of dmPFC and pSTS in coupling prior knowledge about deceptive intents with observed action kinematics in order to judge faked actions. Our study provides causal evidence that fronto-temporal nodes of the ToMn are functionally relevant to mental state inference during action observation.

Disrupting nociceptive information processing flow through transcranial focused ultrasound neuromodulation of thalamic nuclei

BACKGROUND

MRI-guided transcranial focused ultrasound (MRgFUS) as a next-generation neuromodulation tool can precisely target and stimulate deep brain regions with high spatial selectivity. Combined with MR-ARFI (acoustic radiation force imaging) and using fMRI BOLD signal as functional readouts, our previous studies have shown that low-intensity FUS can excite or suppress neural activity in the somatosensory cortex.

OBJECTIVE

To investigate whether low-intensity FUS can suppress nociceptive heat stimulation-induced responses in thalamic nuclei during hand stimulation, and to determine how this suppression influences the information processing flow within nociception networks.

FINDINGS

BOLD fMRI activations evoked by 47.5 °C heat stimulation of hand were detected in 24 cortical regions, which belong to sensory, affective, and cognitive nociceptive networks. Concurrent delivery of low-intensity FUS pulses (650 kHz, 550 kPa) to the predefined heat nociceptive stimulus-responsive thalamic centromedial_parafascicular (CM_para), mediodorsal (MD), ventral_lateral (VL_ and ventral_lateral_posteroventral (VLpv) nuclei suppressed their heat responses. Off-target cortical areas exhibited reduced, enhanced, or no significant fMRI signal changes, depending on the specific areas. Differentiable thalamocortical information flow during the processing of nociceptive heat input was observed, as indicated by the time to reach 10% or 30% of the heat-evoked BOLD signal peak. Suppression of thalamic heat responses significantly altered nociceptive processing flow and direction between the thalamus and cortical areas. Modulation of contralateral versus ipsilateral areas by unilateral thalamic activity differed. Signals detected in high-order cortical areas, such as dorsal frontal (DFC) and ventrolateral prefrontal (vlPFC) cortices, exhibited faster response latencies than sensory areas.

CONCLUSIONS

The concurrent delivery of FUS suppressed nociceptive heat response in thalamic nuclei and disrupted the nociceptive network. This study offers new insights into the causal functional connections within the thalamocortical networks and demonstrates the modulatory effects of low-intensity FUS on nociceptive information processing.

Cognitive Functions following Trigeminal Neuromodulation

Vast scientific effort in recent years have been focused on the search for effective and safe treatments for cognitive decline. In this regard, non-invasive neuromodulation has gained increasing attention for its reported effectiveness in promoting the recovery of multiple cognitive domains after central nervous system damage. In this short review, we discuss the available evidence supporting a possible cognitive effect of trigeminal nerve stimulation (TNS). In particular, we ask that, while TNS has been widely and successfully used in the treatment of various neuropsychiatric conditions, as far as research in the cognitive field is concerned, where does TNS stand? The trigeminal nerve is the largest cranial nerve, conveying the sensory information from the face to the trigeminal sensory nuclei, and from there to the thalamus and up to the somatosensory cortex. On these bases, a bottom-up mechanism has been proposed, positing that TNS-induced modulation of the brainstem noradrenergic system may affect the function of the brain networks involved in cognition. Nevertheless, despite the promising theories, to date, the use of TNS for cognitive empowering and/or cognitive decline treatment has several challenges ahead of it, mainly due to little uniformity of the stimulation protocols. However, as the field continues to grow, standardization of practice will allow for data comparisons across studies, leading to optimized protocols targeting specific brain circuitries, which may, in turn, influence cognition in a designed manner.

Ultrasonic neuromodulation mediated by mechanosensitive ion channels: current and future

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

Non-invasive enhancement of intracortical solute clearance using transcranial focused ultrasound

Transport of interstitial fluid and solutes plays a critical role in clearing metabolic waste from the brain. Transcranial application of focused ultrasound (FUS) has been shown to promote localized cerebrospinal fluid solute uptake into the brain parenchyma; however, its effects on the transport and clearance of interstitial solutes remain unknown. We demonstrate that pulsed application of low-intensity FUS to the rat brain enhances the transport of intracortically injected fluorescent tracers (ovalbumin and high molecular-weight dextran), yielding greater parenchymal tracer volume distribution compared to the unsonicated control group (ovalbumin by 40.1% and dextran by 34.6%). Furthermore, FUS promoted the drainage of injected interstitial ovalbumin to both superficial and deep cervical lymph nodes (cLNs) ipsilateral to sonication, with 78.3% higher drainage observed in the superficial cLNs compared to the non-sonicated hemisphere. The application of FUS increased the level of solute transport visible from the dorsal brain surface, with ~ 43% greater area and ~ 19% higher fluorescence intensity than the unsonicated group, especially in the pial surface ipsilateral to sonication. The sonication did not elicit tissue-level neuronal excitation, measured by an electroencephalogram, nor did it alter the molecular weight of the tracers. These findings suggest that nonthermal transcranial FUS can enhance advective transport of interstitial solutes and their subsequent removal in a completely non-invasive fashion, offering its potential non-pharmacological utility in facilitating clearance of waste from the brain.

Neuronal activity and remyelination: new insights into the molecular mechanisms and therapeutic advancements

This article reviews the role of neuronal activity in myelin regeneration and the related neural signaling pathways. The article points out that neuronal activity can stimulate the formation and regeneration of myelin, significantly improve its conduction speed and neural signal processing ability, maintain axonal integrity, and support axonal nutrition. However, myelin damage is common in various clinical diseases such as multiple sclerosis, stroke, dementia, and schizophrenia. Although myelin regeneration exists in these diseases, it is often incomplete and cannot promote functional recovery. Therefore, seeking other ways to improve myelin regeneration in clinical trials in recent years is of great significance. Research has shown that controlling neuronal excitability may become a new intervention method for the clinical treatment of demyelinating diseases. The article discusses the latest research progress of neuronal activity on myelin regeneration, including direct or indirect stimulation methods, and the related neural signaling pathways, including glutamatergic, GABAergic, cholinergic, histaminergic, purinergic and voltage-gated ion channel signaling pathways, revealing that seeking treatment strategies to promote myelin regeneration through precise regulation of neuronal activity has broad prospects.

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.

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

BACKGROUND

Transcranial ultrasound stimulation (TUS) is a novel non-invasive brain stimulation technique with high depth penetrance and spatial resolution. Theta-burst TUS (tbTUS) is a plasticity-inducing protocol which increases motor cortical excitability for up to 30 min following 80s of sonication. While this protocol may have therapeutic potential for the treatment of psychiatric and neurological disorders, the mechanisms of action of TUS remain unclear.

OBJECTIVE

We conducted the first pharmacological study to examine the mechanisms of TUS in human primary motor cortex. By administering brain-active drugs with known mechanisms of action, we aimed to elucidate the mechanisms of tbTUS.

METHODS

Fourteen healthy subjects participated in a within-subjects randomized, double-blind, cross-over study with five visits. At each visit, one of four study drugs (carbamazepine - Na+ channel blocker, nimodipine - L-type Ca2+ channel blocker, lorazepam - positive allosteric modulator of gamma-aminobutyric acid (GABA) type A receptor, dextromethorphan - N-methyl-d-aspartate receptor antagonist) or placebo was administered in random order, followed by tbTUS.

RESULTS

The plasticity effects of tbTUS on motor cortex excitability measured by motor-evoked potential amplitudes elicited by transcranial magnetic stimulation were reduced by all study drugs compared to placebo.

CONCLUSION

tbTUS may induce NMDA-dependent synaptic plasticity since the effects are blocked by increased GABAA receptor activities and voltage-gated Na+ and Ca2+ channels blockers. These results are consistent with the hypotheses that tbTUS induced long-term potentiation-like mechanisms and that TUS involves activation of mechanosensitive Na+ and Ca2+ channels. Alternatively, non-specific pharmacologically induced changes in excitatory/inhibitory balance might have interfered with the effects of tbTUS.

Nonpharmacological modulation of cortical spreading depolarization

AIMS

Cortical spreading depolarization (CSD) is a wave of pathologic neuronal dysfunction that spreads through cerebral gray matter, causing neurologic disturbance in migraine and promoting lesion development in acute brain injury. Pharmacologic interventions have been found to be effective in migraine with aura, but their efficacy in acutely injured brains may be limited. This necessitates the assessment of possible adjunctive treatments, such as nonpharmacologic methods. This review aims to summarize currently available nonpharmacological techniques for modulating CSDs, present their mechanisms of action, and provide insight and future directions for CSD treatment.

MAIN METHODS

A systematic literature review was performed, generating 22 articles across 3 decades. Relevant data is broken down according to method of treatment.

KEY FINDINGS

Both pharmacologic and nonpharmacologic interventions can mitigate the pathological impact of CSDs via shared molecular mechanisms, including modulating K⁺/Ca²⁺/Na⁺/Cl^- ion channels and NMDA, GABA_A, serotonin, and CGRP ligand-based receptors and decreasing microglial activation. Preclinical evidence suggests that nonpharmacologic interventions, including neuromodulation, physical exercise, therapeutic hypothermia, and lifestyle changes can also target unique mechanisms, such as increasing adrenergic tone and myelination and modulating membrane fluidity, which may lend broader modulatory effects. Collectively, these mechanisms increase the electrical initiation threshold, increase CSD latency, slow CSD velocity, and decrease CSD amplitude and duration.

SIGNIFICANCE

Given the harmful consequences of CSDs, limitations of current pharmacological interventions to inhibit CSDs in acutely injured brains, and translational potentials of nonpharmacologic interventions to modulate CSDs, further assessment of nonpharmacologic modalities and their mechanisms to mitigate CSD-related neurologic dysfunction is warranted.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Non-invasive neuromodulation of sub-regions of the human insula differentially affect pain processing and heart-rate variability

The insula is a portion of the cerebral cortex folded deep within the lateral sulcus covered by the overlying opercula of the inferior frontal lobe and superior portion of the temporal lobe. The insula has been parsed into sub-regions based upon cytoarchitectonics and structural and functional connectivity with multiple lines of evidence supporting specific roles for each of these sub-regions in pain processing and interoception. In the past, causal interrogation of the insula was only possible in patients with surgically implanted electrodes. Here, we leverage the high spatial resolution combined with the deep penetration depth of low-intensity focused ultrasound (LIFU) to non-surgically modulate either the anterior insula (AI) or posterior insula (PI) in humans for effect on subjective pain ratings, electroencephalographic (EEG) contact head evoked potentials (CHEPs) and time-frequency power as well as autonomic measures including heart-rate variability (HRV) and electrodermal response (EDR). N = 23 healthy volunteers received brief noxious heat pain stimuli to the dorsum of their right hand during continuous heart-rate, EDR and EEG recording. LIFU was delivered to either the AI (anterior short gyrus), PI (posterior longus gyrus) or under an inert sham condition time-locked to the heat stimulus. Results demonstrate that single-element 500 kHz LIFU is capable of individually targeting specific gyri of the insula. LIFU to both AI and PI similarly reduced perceived pain ratings but had differential effects on EEG activity. LIFU to PI affected earlier EEG amplitudes around 300 milliseconds whereas LIFU to AI affected EEG amplitudes around 500 milliseconds. In addition, only LIFU to the AI affected HRV as indexed by an increase in standard deviation of N-N intervals (SDNN) and mean HRV low frequency power. There was no effect of LIFU to either AI or PI on EDR or blood pressure. Taken together, LIFU looks to be an effective method to individually target sub-regions of the insula in humans for site-specific effects on brain biomarkers of pain processing and autonomic reactivity that translates to reduced perceived pain to a transient heat stimulus. These data have implications for the treatment of chronic pain and several neuropsychological diseases like anxiety, depression and addiction that all demonstrate abnormal activity in the insula concomitant with dysregulated autonomic function.

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.

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.

Neural Correlates of Delay Discounting in the Light of Brain Imaging and Non-Invasive Brain Stimulation: What We Know and What Is Missed

In decision making, the subjective value of a reward declines with the delay to its receipt, describing a hyperbolic function. Although this phenomenon, referred to as delay discounting (DD), has been extensively characterized and reported in many animal species, still, little is known about the neuronal processes that support it. Here, after drawing a comprehensive portrait, we consider the latest neuroimaging and lesion studies, the outcomes of which often appear contradictory among comparable experimental settings. In the second part of the manuscript, we focus on a more recent and effective route of investigation: non-invasive brain stimulation (NIBS). We provide a comprehensive review of the available studies that applied transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) to affect subjects’ performance in DD tasks. The aim of our survey is not only to highlight the superiority of NIBS in investigating DD, but also to suggest targets for future experimental studies, since the regions considered in these studies represent only a fraction of the possible ones. In particular, we argue that, based on the available neurophysiological evidence from lesion and brain imaging studies, a very promising and underrepresented region for future neuromodulation studies investigating DD is the orbitofrontal cortex.

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

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

Weak Ultrasound Contributes to Neuromodulatory Effects in the Rat Motor Cortex

Transcranial focused ultrasound (tFUS) is a novel neuromodulating technique. It has been demonstrated that the neuromodulatory effects can be induced by weak ultrasound exposure levels (spatial-peak temporal average intensity, I_SPTA < 10 mW/cm²) in vitro. However, fewer studies have examined the use of weak tFUS to potentially induce long-lasting neuromodulatory responses in vivo. The purpose of this study was to determine the lower-bound threshold of tFUS stimulation for inducing neuromodulation in the motor cortex of rats. A total of 94 Sprague-Dawley rats were used. The sonication region aimed at the motor cortex under weak tFUS exposure (I_SPTA of 0.338-12.15 mW/cm²). The neuromodulatory effects of tFUS on the motor cortex were evaluated by the changes in motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS). In addition to histology analysis, the in vitro cell culture was used to confirm the neuromodulatory mechanisms following tFUS stimulation. In the results, the dose-dependent inhibitory effects of tFUS were found, showing increased intensities of tFUS suppressed MEPs and lasted for 30 min. Weak tFUS significantly decreased the expression of excitatory neurons and increased the expression of inhibitory GABAergic neurons. The PIEZO-1 proteins of GABAergic neurons were found to involve in the inhibitory neuromodulation. In conclusion, we show the use of weak ultrasound to induce long-lasting neuromodulatory effects and explore the potential use of weak ultrasound for future clinical neuromodulatory applications.