Noninvasive Submillimeter-Precision Brain Stimulation by Optically-Driven Focused Ultrasound

High precision neuromodulation is a powerful tool to decipher neurocircuits and treat neurological diseases. Current non-invasive neuromodulation methods offer limited millimeter-level precision. Here, we report an optically-driven focused ultrasound (OFUS) for non-invasive brain stimulation with submillimeter precision. OFUS is generated by a soft optoacoustic pad (SOAP) fabricated through embedding candle soot nanoparticles in a curved polydimethylsiloxane film. SOAP generates a transcranial ultrasound focus at 15 MHz with a lateral resolution of 83 micrometers, which is two orders of magnitude smaller than that of conventional transcranial focused ultrasound (tFUS). Effective OFUS neurostimulation in vitro with a single ultrasound cycle is shown. Submillimeter transcranial stimulation of mouse motor cortex in vivo is demonstrated. An acoustic energy of 0.02 J/cm^2, two orders of magnitude less than that of tFUS, is sufficient for successful OFUS neurostimulation. By delivering a submillimeter focus non-invasively, OFUS opens a new way for neuroscience studies and disease treatments.Comment: 36 pages, 5 main figures, 13 supplementary figure

Focused Ultrasound Stimulation as a Neuromodulatory Tool for Parkinson’s Disease::A Scoping Review

Non-invasive focused ultrasound stimulation (FUS) is a non-ionising neuromodulatory technique that employs acoustic energy to acutely and reversibly modulate brain activity of deep-brain structures. It is currently being investigated as a potential novel treatment for Parkinson’s disease (PD). This scoping review was carried out to map available evidence pertaining to the provision of FUS as a PD neuromodulatory tool. In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Extension for Scoping Reviews, a search was applied to Ovid MEDLINE, Embase, Web of Science and Cochrane Central Register of Controlled Trials on 13 January 2022, with no limits applied. In total, 11 studies were included: 8 were from China and 1 each from Belgium, South Korea and Taiwan. All 11 studies were preclinical (6 in vivo, 2 in vitro, 2 mix of in vivo and in vitro and 1 in silico). The preclinical evidence indicates that FUS is safe and has beneficial neuromodulatory effects on motor behaviour in PD. FUS appears to have a therapeutic role in influencing the disease processes of PD, and therefore holds great promise as an attractive and powerful neuromodulatory tool for PD. Though these initial studies are encouraging, further study to understand the underlying cellular and molecular mechanisms is required before FUS can be routinely used in PD

Focused ultrasound excites neurons via mechanosensitive calcium accumulation and ion channel amplification

Ultrasonic neuromodulation has the unique potential to provide non-invasive control of neural activity in deep brain regions with high spatial precision and without chemical or genetic modification. However, the biomolecular and cellular mechanisms by which focused ultrasound excites mammalian neurons have remained unclear, posing significant challenges for the use of this technology in research and potential clinical applications. Here, we show that focused ultrasound excites neurons through a primarily mechanical mechanism mediated by specific calcium-selective mechanosensitive ion channels. The activation of these channels results in a gradual build-up of calcium, which is amplified by calcium- and voltage-gated channels, generating a burst firing response. Cavitation, temperature changes, large-scale deformation, and synaptic transmission are not required for this excitation to occur. Pharmacological and genetic inhibition of specific ion channels leads to reduced responses to ultrasound, while over-expressing these channels results in stronger ultrasonic stimulation. These findings provide a critical missing explanation for the effect of ultrasound on neurons and facilitate the further development of ultrasonic neuromodulation and sonogenetics as unique tools for neuroscience research

Ultrasound neuromodulation: a review of results, mechanisms and safety

Ultrasonic neuromodulation is a rapidly growing field, in which low-intensity ultrasound (US) is delivered to nervous system tissue, resulting in transient modulation of neural activity. This review summarizes the findings in the central and peripheral nervous systems from mechanistic studies in cell culture to cognitive behavioral studies in humans. The mechanisms by which US mechanically interacts with neurons and could affect firing are presented. An in-depth safety assessment of current studies shows that parameters for the human studies fall within the safety envelope for US imaging. Challenges associated with accurately targeting US and monitoring the response are described. In conclusion, the literature supports the use of US as a safe, non-invasive brain stimulation modality with improved spatial localization and depth targeting compared with alternative methods. US neurostimulation has the potential to be used both as a scientific instrument to investigate brain function and as a therapeutic modality to modulate brain activity

Modulation of cerebellar purkinje cell activity with low intensity electric and ultrasound stimulation

Non-invasive brain stimulation (NIBS) techniques garner significant interest due to their potential to offer instantaneous and region-specific treatments to neurological disorders. The cerebellum is one of the target sites for NIBS methods due to its central role in motor and cognitive functions. Among several modulation techniques, transcranial electric stimulations (tEs), in particular, transcranial direct and alternating current stimulations (tDCs/tACs), and low intensity focused ultrasound stimulation (LIFUS) show encouraging outcomes in clinical applications. tDCs and tACs are favored due to their low cost and accessibility while LIFUS offers high spatial resolution and deeper penetration without affecting the surrounding structures. In order to better understand the underlying mechanism of these methods in the cerebellum, animal studies are needed since these experiments require invasive surgeries. The goal of this study is to investigate the response of cerebellar PCs to electric and ultrasound stimulation in an animal model. The first objective is to measure the electric field (e-field) distribution inside the brain parenchyma since e-field is the main parameter that determines the local effects of electrical stimulation. The results of this part show that e-field decays exponentially through horizontal and vertical directions from the stimulating electrode and scattered by the skin up to 80%. Then, tACS and tDCS are applied to the cerebellar cortex respectively while recording the extracellular spike activity from the cerebellar PCs. The activity of PCs is important because they generate the sole output from the cerebellar cortex, which in turn modifies the output of the deep cerebellar nuclei (DCN). The results of this part demonstrate that the direction of e-field is highly correlated with the level of modulation measured on the PCs. Applying the e-field parallel to the dendritic tree of the PCs generates the highest modulation level. Our data show that PCs have a characteristic response to both DC and AC fields, including entrainment of the simple spike activity at high frequencies. Our findings for the LIFUS also show that spike timing of PCs is strongly entrained with the pulsed ultrasound stimulation, and the level of the entrainment is inversely correlated with the pulse width. In summary, the low intensity electric and ultrasound stimulation are able to effectively modulate the PC activity in the cerebellar cortex. This warrants research to further look into the mechanism of tES and LIFUS acting on the cerebellar cortex at the cellular level

Modulating microcircuits in depression

Major depressive disorder (MDD) is globally the leading cause of disability with a worldwide prevalence of 4.4 %, affecting 322 million people in 2015. The treatment of MDD includes antidepressant medication and psychological therapies. However, approximately one-third of treated patients do not respond adequately to these treatments. These patients suffer from treatment-resistant depression (TRD). Deep brain stimulation (DBS) is a therapy modality widely researched for TRD, however, study outcomes show inconsistent results. This thesis focuses on DBS in TRD and researches i) if it is possible to disentangle TRD into different microcircuits, ii) how clinical DBS outcomes can be improved and iii) if DBS can be refined with a non-invasive technique called magnetothermal DBS (mDBS) introducing nanomaterial-mediated neuromodulation. MDBS is researched in collaboration with the research group of prof. dr. P. Anikeeva at the research laboratory of electronics (rle) at the Massachusetts Institute of Technology (MIT) (Boston, USA)

Mechanism of transcranial focused ultrasound regulating the neuronal activity of the retrosplenial cortex

Non-invasive neuromodulation is crucial in fundamental research and clinical treatment. Among those non-invasive neuromodulations, transcranial focused ultrasound (tFUS) can penetrate the skull to focus energy on a specific brain region, temporarily affecting brain function. Compared with traditional neuromodulation methods, such as transcranial direct current stimulation and transcranial magnetic stimulation, tFUS has become a novel method for regulating neuronal activity by means of its non-invasion, reversibility, and accuracy. However, how tFUS regulates neuronal activity and cellular properties in response to tFUS remains unknown. To investigate how tFUS regulates neuronal activity, I used behavioural tests, real-time fluorescence quantitative polymerase chain reaction, immunofluorescent staining, chemical genetics, and multi-channel in vivo recording to explore whether tFUS affected neuronal activity in the pain-related brain region, retrosplenial cortex (RSC). Moreover, tFUS significantly increased paw withdrawal threshold (PWT) and prolonged thermal withdrawal latency (TWL) both in naïve and neuropathic mice. tFUS also significantly increased mRNA and protein expression levels of early growth factor response 1 (Egr1). These tFUS-activated Egr1 cells were mainly neurons. Through multi-channel in vivo recording, it was found that the spike rate of pyramidal neurons and interneurons decreased remarkably under tFUS. A greater proportion of spike rate in pyramidal neurons and interneurons showed a decrease rather than an Subsequently, Egr1 positive cells activated by tFUS were specifically inhibited by the targeted recombination in the active population system (TRAP), and then the effect of tFUS on PWT and TWL was inhibited. These results suggested that Egr1 was an essential marker of tFUS responsive neurons in RSC. Subsequently, I performed transcriptome sequencing based on Egr1-GFP cells activated by tFUS. Transient receptor potential cation channel subfamily C member 4 (Trpc4) was selected according to the transcriptome sequencing data. Combined with calcium imaging, patch-clamp recording, and short hairpin ribonucleic acid (shRNA) interference, it was found that tFUS could activate Trpc4, which could be blocked by ML204, an inhibitor of Trpc4. In vivo, with specific inhibition of Trpc4 expression in RSC, the proportion of decreased neuronal activity induced by tFUS was significantly down-regulated. At the same time, the regulation of PWT and TWL by tFUS was also inhibited. The above results showed that Trpc4 was an important factor in regulating Egr1 response to tFUS, thus regulating RSC and further regulating the somatosensory threshold of mice. To further explore the characteristics of tFUS responsive cells, I used single-cell RNA sequencing (scRNA-seq) to map the single-cell transcriptome expression of RSC. It was also identified tFUS-induced cell type-dependent transcriptome and functional changes in RSC. Subsequently, Egr1 was used as a marker to identify tFUS-activated cell types and populations. Then, it was found that Egr1 was highly expressed in neurons, endothelial cells (EC), and vascular smooth muscle cells (vSMC). These cells acted as tFUS-sensitive cells. Further analysis of cellular communication pathways between tFUS-sensitive cells and other cells revealed multiple signal pathways, which suggested that tFUS- sensitive cells received or transmitted information to other cell types, causing changes in the transcriptome. In conclusion, this study found that Trpc4 was a key factor regulating Egr1 response to tFUS. In addition, it provided transcriptome expression atlas and cellular communication pathways of tFUS-sensitive cells by scRNA-seq. These results provided a basis for the cellular and molecular mechanisms of tFUS neuromodulation, which supported ultrasonic neuromodulation in basic neuroscience research and clinical applications

High precision optoacoustic neural modulation

Manipulation of brain circuits is a critical to understanding how brain controls behaviors under normal physiological conditions and how its dysfunction causes diseases. Ultrasound stimulation is an emerging neuromodulation modality that allows activation of neurons with acoustic waves. However, the piezo based transcranial ultrasound stimulation offers poor spatial resolution, which hinders the understanding of its mechanism as well as application in region specific activation in small animals. To address this limitation, we developed a series of neuromodulation techniques utilizing the photon to sound conversion capability offered by the optoacoustic effect. In chapter 2, we developed a fiber based optoacoustic converter th-at allows neural stimulation at submillimeter spatial precision both in vitro and in vivo. In chapter 3, the spatial resolution was further improved by tapered fiber optoacoustic emitter to achieve stimulation of single neurons and even subcellular structures in culture. In chapter 4, we developed photoacoustic nanoparticle based neural stimulation that allows direct activation of neurons through optoacoustic waves generated by nanoparticles bonded to the neuronal membrane. Finally, in chapter 5, in an effort to improve penetration depth, a split ring resonator based microwave neuromodulation was developed that allows wireless stimulation and inhibition of neurons with subwavelength spatial resolution. Together, these methods offer an enabling platform with opportunities to understand the mechanism of acoustic neural stimulation as well as potential for treatment of neurological diseases with high precision neuromodulation

Neuroenhancement in Military Personnel::Conceptual and Methodological Promises and Challenges

Military personnel face harsh conditions that strain their physical and mental well-being, depleting resources necessary for sustained operational performance. Future operations will impose even greater demands on soldiers in austere environments with limited support, and new training and technological approaches are essential. This report highlights the progress in cognitive neuroenhancement research, exploring techniques such as neuromodulation and neurofeedback, and emphasizes the inherent challenges and future directions in the field of cognitive neuroenhancement for selection, training, operations, and recovery