Transcranial ultrasonic stimulation (TUS) is an emerging non-invasive brain stimulation technique that has higher spatial resolution than electrical and magnetic stimulation approaches, and, uniquely, offers the ability to target structures deep in the brain. Early work in humans suggests that TUS can both evoke neural activity [[1]Lee W. Kim H.C. Jung Y. Chung Y.A. Song I.U. Lee J.H. et al.Transcranial focused ultrasound stimulation of human primary visual cortex.Sci Rep. 2016; 6: 1-12PubMed Google Scholar] and modulate activity elicited by other stimuli [[2]Legon W. Sato T.F. Opitz A. Mueller J. Barbour A. Williams A. et al.Transcranial focused ultrasound modulates the activity of primary somatosensory cortex in humans.Nat Neurosci. 2014; 17: 322-329Crossref PubMed Scopus (553) Google Scholar]. However, the protocols used in these studies may be audible due to the sharp onset and offset of ultrasound energy [[3]Johnstone A. Nandi T. Martin E. Bestmann S. Stagg C. Treeby B. A range of pulses commonly used for human transcranial ultrasound stimulation are clearly audible.Brain Stimul: Basic. Trans. Clin. Res. Neuromodulation. 2021; 14: 1353-1355Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar,[4]Mohammadjavadi M. Ye P.P. Xia A. Brown J. Popelka G. Pauly K.B. Elimination of peripheral auditory pathway activation does not affect motor responses from ultrasound neuromodulation.Brain Stimul. 2019; 12: 901-910Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar], and it is therefore possible that there is an auditory confound to the observed effects [[5]Braun V. Blackmore J. Cleveland R.O. Butler C.R. Transcranial ultrasound stimulation in humans is associated with an auditory confound that can be effectively masked.Brain Stimul. 2020; 13: 1527-1534Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar]. Here, therefore, we used a less audible, ramped protocol [[3]Johnstone A. Nandi T. Martin E. Bestmann S. Stagg C. Treeby B. A range of pulses commonly used for human transcranial ultrasound stimulation are clearly audible.Brain Stimul: Basic. Trans. Clin. Res. Neuromodulation. 2021; 14: 1353-1355Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar] to determine if we could either evoke or modulate activity in the primary visual cortex (V1). We examined whether V1 TUS alone evokes neural activity detectable in the EEG, and whether TUS modulates visual evoked potentials (VEPs) in response to a pattern-reversal checkerboard stimulus. Fourteen healthy participants (4 female, 31 ± 4.3 years) were included in the study, after excluding three participants due to technical problems. The project was approved by the UCL research ethics committee (Project ID 14071/001). As described in our previous paper [[3]Johnstone A. Nandi T. Martin E. Bestmann S. Stagg C. Treeby B. A range of pulses commonly used for human transcranial ultrasound stimulation are clearly audible.Brain Stimul: Basic. Trans. Clin. Res. Neuromodulation. 2021; 14: 1353-1355Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar], TUS was delivered using a 2-element spherically focusing annular array transducer (H115-2AA, Sonic Concepts) with a nominal outer aperture diameter and radius of curvature of 64mm. The transducer was driven at 270 kHz by a 2-channel TPO (Sonic Concepts) with the output power and element phase adjusted to give a focal pressure in water of 700 kPa (spatial peak pulse average intensity without ramping of 16 W/cm2) and a focal distance of 43 mm. The measured −3 dB focal size in water was 5 mm (lateral) by 30 mm (axial). Ramped pulses (1 ms Tukey ramp, 3.25 ms total pulse duration) were applied at a pulse repetition frequency (PRF) of 250 Hz, with a pulse train duration of 300 ms and an effective duty cycle of 50%. Of the 14 participants, 7 could not hear the stimulation at all, while the rest were either uncertain or heard it faintly. EEG was recorded from 16 channels (Fig. 1a), at 600 Hz, using the g.USBamp amplifier (g.tec medical engineering GmbH). Participants were positioned in a chin rest. The transducer, connected to an articulated arm, was manually positioned 2 cm to the left of the inion and held in place using rubber straps. Acoustic coupling was achieved using a gel pad and ultrasound gel. Participants were dark adapted for 2 min before starting stimulation and then sat facing a screen 50–60 cm away. First, in two TUS-only blocks, real and sham pulses (100 each), were applied randomly at a fixed inter-stimulus interval of 2 s. Then, two TUS + checkerboard blocks were performed, where a checkerboard stimulus (checks at 25 and 75% of maximum screen luminance, and ∼32° visual angle) was flipped every 0.5 s, and every fourth stimulus was associated with either a real or sham (100 each) TUS trial. The TUS trial started 130 ms (±0–5 ms jitter) before the checkerboard flip. Real and sham trials within each block were randomised and double-blind. EEG data were analysed using eeglab (https://eeglab.org/) and FieldTrip (http://fieldtriptoolbox.org). The data were epoched relative to the TUS onset (−0.5 to 0.5 s) for TUS-only blocks, and relative to the checkerboard flip (−0.2 to 0.3 s) for TUS + checkerboard blocks. The following filters were applied: 50 Hz bandstop, 45 Hz lowpass and 1 Hz highpass, and the data were baseline corrected (−100 to 0 ms TUS-only, and −200 to −140 TUS + checkerboard). Across participants and conditions 14 ± 7 trials were rejected using z-value based artifact detection with a cut-off of 15. After time-locked averaging, cluster-based permutation testing was used to examine differences between pairs of conditions across all channels. In the TUS-only blocks, we did not observe any evoked potentials, and found no significant differences between real and sham TUS conditions (Fig. 1b). In contrast to previous reports, none of our participants reported phosphenes. As would be expected, in the TUS + checkerboard blocks, a clear VEP in response to the visual checkerboard was observed in all conditions. A statistically significant difference was observed between real and no TUS trials, in posterior electrodes, during a time period corresponding to the N75 component of the VEP, which likely originates in V1 (Fig. 1c). There was no difference between the sham and no TUS condition, but also no significant difference when the real and sham conditions were directly compared. Our findings differ from previous work which showed that TUS applied to the V1 evokes a 'VEP-like' potential [[1]Lee W. Kim H.C. Jung Y. Chung Y.A. Song I.U. Lee J.H. et al.Transcranial focused ultrasound stimulation of human primary visual cortex.Sci Rep. 2016; 6: 1-12PubMed Google Scholar]. While we used the same intensity as this previous study, in order to implement effective ramping, we lowered the PRF. Though some in vitro and animal data suggest that higher PRFs lead to stronger effects [[6]King R.L. Brown J.R. Newsome W.T. Pauly K.B. Effective parameters for ultrasound-induced in vivo neurostimulation.Ultrasound Med Biol. 2013; 39: 312-331Abstract Full Text Full Text PDF PubMed Scopus (311) Google Scholar,[7]Manuel T.J. Kusunose J. Zhan X. Lv X. Kang E. Yang A. et al.Ultrasound neuromodulation depends on pulse repetition frequency and can modulate inhibitory effects of TTX.Sci Rep. 2020; 10: 1-10Crossref PubMed Scopus (23) Google Scholar], the parameter space has not been extensively mapped, and in humans neuromodulatory effects have been demonstrated at PRFs similar to ours [[8]Liu C. Yu K. Niu X. He B. Transcranial focused ultrasound enhances sensory discrimination capability through somatosensory cortical excitation.Ultrasound Med Biol. 2021; 47: 1356-1366Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar]. As such, while the differences in parameters may have contributed to the lack of TUS-evoked activity in our study, we cannot rule out the possibility that effects reported previously were influenced by an auditory confound, in particular since the limited number of EEG channels did not allow localizing the anatomical origin of the evoked potential. Adding to previous work showing modulatory TUS effects [[2]Legon W. Sato T.F. Opitz A. Mueller J. Barbour A. Williams A. et al.Transcranial focused ultrasound modulates the activity of primary somatosensory cortex in humans.Nat Neurosci. 2014; 17: 322-329Crossref PubMed Scopus (553) Google Scholar], we observed increased amplitude of the VEP N75 component. Modulation of the N75 amplitude has also been reported in response to transcranial magnetic and electrical stimulation [[9]Vallar G. Bolognini N. Behavioural facilitation following brain stimulation: implications for neurorehabilitation.Neuropsychol Rehabil. 2011; 21: 618-649Crossref PubMed Scopus (76) Google Scholar], and can be accompanied by a change in contrast sensitivity [[10]Nakazono H. Ogata K. Takeda A. Yamada E. Kimura T. Tobimatsu S. Transcranial alternating current stimulation of α but not β frequency sharpens multiple visual functions.Brain Stimul. 2020; 13: 343-352Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar]. Our data suggest that TUS can be added to the repertoire of non-invasive brain stimulation tools to study the physiological basis of visual perception, and more generally, to modulate neural activity for basic science and clinical applications. However, we did not find any differences between sham and real TUS conditions, likely due to fewer trials in these conditions compared to the no TUS VEPs (100 vs 300), but replication studies are required to draw definitive conclusions. In conclusion, we demonstrate that ramped TUS, which is less audible than pulsing regimes with sharp onsets and offsets, can modulate neural activity. This suggests that, in line with in-vitro and animal data, there is a direct neuromodulatory effect of ultrasound, in addition to any confounding effects. Moving forward, ramping offers a relatively easy approach to minimise the auditory confound. Raw EEG data has been uploaded to https://osf.io/rbcfy/ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. This work was supported by the Engineering and Physical Sciences Research Council UK (EP/P008860/1, EP/P008712/1, EP/S026371/1). EM was supported by a UKRI Future Leaders Fellowship (MR/T019166/1) and in part by the Wellcome/EPSRC Centre for Interventional and Surgical Sciences (WEISS) (203145Z/16/Z). CZ is supported by the Brain Research UK (201718-13). SB was supported by the Dunhill Medical Trust, (RPGF1810∖93). TN was supported by a grant from the Boehringer Ingelheim Foundation (BIS) to TOB. The research was supported by the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre and the NIHR Oxford Health Biomedical Research Centre. The Wellcome Centre for Integrative Neuroimaging is supported by core funding from the Wellcome Trust (203139/Z/16/Z). CJS holds a Senior Research Fellowship, funded by the Wellcome Trust (224430/Z/21/Z).
Abstract Background Neurofibromatosis 1 (NF1) is a single-gene disorder associated with cognitive phenotypes common to neurodevelopmental conditions such as Autism Spectrum Disorder (ASD) & Attention Deficit Hyperactivity Disorder (ADHD). GABAergic dysregulation underlies working memory impairments seen in NF1. This mechanistic experimental study investigates how inter-individual differences in GABA relate to working memory and whether application of anodal transcranial direct current stimulation (atDCS) can modulate of GABA and working memory. Methods 31 adolescents with NF1 were recruited to a single-blind, sham-controlled cross-over trial. Baseline assessments included detailed working memory tests and parent reported measures. Each participant had two study visits, one with atDCS and another with sham intervention applied to the left Dorsolateral Prefrontal Cortex (DLPFC) inside the scanner. Magnetic Resonance Spectroscopy was collected before and after aTDCS/sham intervention in the left DLPFC and occipital cortex. Results Higher baseline GABA was associated with faster response times (RT) on verbal and visuospatial working memory measures. No correlation was observed between baseline GABA and working memory accuracy. AtDCS was associated with significantly greater reduction in GABA, as compared to sham in the left DLPFC. There was no effect of atDCS on Glx in left DLPFC and no significant effect of atDCS on GABA or Glx in the occipital cortex. There was no effect of atDCS on behavioural measures of working memory. Limitations Limitations of this study include use of brief behavioural outcome measures post tDCS chosen to reduce participant burden and the lack of a healthy control group. The GABA levels measured in this study will contain contributions from co-edited macromolecule signal (so-called GABA+), but the relative contribution of these macromolecular signals are thought to be constant unlikely to account for within participant/session GABA changes. Conclusions This first such study in adolescents with NF1, showed that atDCS modulates inhibitory activity in the DLPFC. This focussed mechanism trial presents a highly promising approach to understanding complex neural pathology in neurodevelopmental disorders. Given the strong evidence linking GABA abnormalities to cognitive deficits across neurodevelopmental conditions such as ASD, modulation of GABA using atDCS offers a promising novel therapeutic approach. ClinicalTrials.gov Identifier: NCT0499142. Registered 5 th August 2021; retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04991428
Transcranial ultrasonic stimulation (TUS) is rapidly emerging as a promising non-invasive neuromodulation technique. TUS is already well-established in animal models, providing foundations to now optimize neuromodulatory efficacy for human applications. Across multiple studies, one promising protocol, pulsed at 1000 Hz, has consistently resulted in motor cortical inhibition in humans (). At the same time, a parallel research line has highlighted the potentially confounding influence of peripheral auditory stimulation arising from TUS pulsing at audible frequencies. In this study, we disentangle direct neuromodulatory and indirect auditory contributions to motor inhibitory effects of TUS. To this end, we include tightly matched control conditions across four experiments, one preregistered, conducted independently at three institutions. We employed a combined transcranial ultrasonic and magnetic stimulation paradigm, where TMS-elicited motor-evoked potentials (MEPs) served as an index of corticospinal excitability. First, we replicated motor inhibitory effects of TUS but showed through both tight controls and manipulation of stimulation intensity, duration, and auditory masking conditions that this inhibition was driven by peripheral auditory stimulation, not direct neuromodulation. Further, we consider neuromodulation beyond driving overall excitation/inhibition and show preliminary evidence of how TUS might interact with ongoing neural dynamics instead. Primarily, this study highlights the substantial shortcomings in accounting for the auditory confound in prior TUS-TMS work where only a flip-over sham and no active control was used. The field must critically reevaluate previous findings given the demonstrated impact of peripheral confounds. Further, rigorous experimental design via (in)active control conditions is required to make substantiated claims in future TUS studies. Only when direct effects are disentangled from those driven by peripheral confounds can TUS fully realize its potential for research and clinical applications.
Transcranial ultrasonic stimulation (TUS) is rapidly emerging as a promising non-invasive neuromodulation technique. TUS is already well-established in animal models, providing foundations to now optimize neuromodulatory efficacy for human applications. Across multiple studies, one promising protocol, pulsed at 1000 Hz, has consistently resulted in motor cortical inhibition in humans (Fomenko et al., 2020). At the same time, a parallel research line has highlighted the potentially confounding influence of peripheral auditory stimulation arising from TUS pulsing at audible frequencies. In this study, we disentangle direct neuromodulatory and indirect auditory contributions to motor inhibitory effects of TUS. To this end, we include tightly matched control conditions across four experiments, one preregistered, conducted independently at three institutions. We employed a combined transcranial ultrasonic and magnetic stimulation paradigm, where TMS-elicited motor-evoked potentials (MEPs) served as an index of corticospinal excitability. First, we replicated motor inhibitory effects of TUS but showed through both tight controls and manipulation of stimulation intensity, duration, and auditory masking conditions that this inhibition was driven by peripheral auditory stimulation, not direct neuromodulation. Furthermore, we consider neuromodulation beyond driving overall excitation/inhibition and show preliminary evidence of how TUS might interact with ongoing neural dynamics instead. Primarily, this study highlights the substantial shortcomings in accounting for the auditory confound in prior TUS-TMS work where only a flip-over sham and no active control was used. The field must critically reevaluate previous findings given the demonstrated impact of peripheral confounds. Furthermore, rigorous experimental design via (in)active control conditions is required to make substantiated claims in future TUS studies. Only when direct effects are disentangled from those driven by peripheral confounds can TUS fully realize its potential for research and clinical applications.
Abstract Transcranial ultrasonic stimulation (TUS) is rapidly emerging as a promising non-invasive neuromodulation technique. TUS is already well-established in animal models, providing foundations to now optimize neuromodulatory efficacy for human applications. Across multiple studies, one promising protocol, pulsed at 1000 Hz, has consistently resulted in motor cortical inhibition in humans (Fomenko et al., 2020). At the same time, a parallel research line has highlighted the potentially confounding influence of peripheral auditory stimulation arising from TUS pulsing at audible frequencies. In this study, we disentangle direct neuromodulatory and indirect auditory contributions to motor inhibitory effects of TUS. To this end, we include tightly matched control conditions across four experiments, one preregistered, conducted independently at three institutions. We employed a combined transcranial ultrasonic and magnetic stimulation paradigm, where TMS-elicited motor-evoked potentials (MEPs) served as an index of corticospinal excitability. First, we replicated motor inhibitory effects of TUS but showed through both tight controls and manipulation of stimulation intensity, duration, and auditory masking conditions that this inhibition was driven by peripheral auditory stimulation, not direct neuromodulation. Further, we consider neuromodulation beyond driving overall excitation/inhibition and show preliminary evidence of how TUS might interact with ongoing neural dynamics instead. Primarily, this study highlights the substantial shortcomings in accounting for the auditory confound in prior TUS-TMS work where only a flip-over sham and no active control was used. The field must critically reevaluate previous findings given the demonstrated impact of peripheral confounds. Further, rigorous experimental design via (in)active control conditions is required to make substantiated claims in future TUS studies. Only when direct effects are disentangled from those driven by peripheral confounds can TUS fully realize its potential for research and clinical applications.
Transcranial ultrasonic stimulation (TUS) is rapidly emerging as a promising non-invasive neuromodulation technique. TUS is already well-established in animal models, providing foundations to now optimize neuromodulatory efficacy for human applications. Across multiple studies, one promising protocol, pulsed at 1000 Hz, has consistently resulted in motor cortical inhibition in humans (Fomenko et al., 2020). At the same time, a parallel research line has highlighted the potentially confounding influence of peripheral auditory stimulation arising from TUS pulsing at audible frequencies. In this study, we disentangle direct neuromodulatory and indirect auditory contributions to motor inhibitory effects of TUS. To this end, we include tightly matched control conditions across four experiments, one preregistered, conducted independently at three institutions. We employed a combined transcranial ultrasonic and magnetic stimulation paradigm, where TMS-elicited motor-evoked potentials (MEPs) served as an index of corticospinal excitability. First, we replicated motor inhibitory effects of TUS but showed through both tight controls and manipulation of stimulation intensity, duration, and auditory masking conditions that this inhibition was driven by peripheral auditory stimulation, not direct neuromodulation. Furthermore, we consider neuromodulation beyond driving overall excitation/inhibition and show preliminary evidence of how TUS might interact with ongoing neural dynamics instead. Primarily, this study highlights the substantial shortcomings in accounting for the auditory confound in prior TUS-TMS work where only a flip-over sham and no active control was used. The field must critically reevaluate previous findings given the demonstrated impact of peripheral confounds. Furthermore, rigorous experimental design via (in)active control conditions is required to make substantiated claims in future TUS studies. Only when direct effects are disentangled from those driven by peripheral confounds can TUS fully realize its potential for research and clinical applications.
For almost 150 years, researchers have been intrigued by the complex neural control of standing balance. Despite accumulating evidence showing cortical involvement, much is yet to be learnt about the nuances of how the motor cortex (M1) tunes muscle activation in standing. This thesis examined the neural input to leg muscles in increasingly difficult standing tasks. It was found that the net output from M1 sets the activation of leg muscles and consequently influences postural sway. This net M1 output is determined by a combination of inhibitory and facilitatory processes which likely account for different aspects of postural control like cognitive influences, planning and preparation for perturbations. Additionally, examination of the synchronized output from the cortex to multiple muscles showed that the cortex favors reciprocal control, which is mechanically advantageous and also costs less energy. Also, such synchronized outputs are tailored to the biomechanical demands of each task. Finally, a preliminary examination of the factors contributing to individual differences in neural control of standing was conducted. Each individual’s intrinsic neural excitability (possibly driven by genetics or plasticity due to previous experiences) influenced how they controlled balance in the increasingly difficult tasks. Additionally, cortical excitability was associated with self-reported balance confidence and likely mediates the effect of this cognitive attribute on motor performance. In conclusion, the findings of this thesis suggest that the cortex plays a role in the higher order planning and processing required for determining muscle activation patterns and maintaining balance in standing.
Low-intensity Transcranial Ultrasonic Stimulation (TUS) is a non-invasive brain stimulation technique enabling cortical and deep brain targeting with unprecedented spatial accuracy. Given the high rate of adoption by new users with varying levels of expertise and interdisciplinary backgrounds, practical guidelines are needed to ensure state-of-the-art TUS application and reproducible outcomes. Therefore, the International Transcranial Ultrasonic Stimulation Safety and Standards (ITRUSST) consortium has formed a subcommittee, endorsed by the International Federation of Clinical Neurophysiology (IFCN), to develop recommendations for best practice in TUS applications in humans. The practical guide presented here provides a brief introduction into ultrasound physics and sonication parameters. It explains the requirements of TUS lab equipment and transducer selection and discusses experimental design and procedures alongside potential confounds and control conditions. Finally, the guide elaborates on essential steps of application planning for stimulation safety and efficacy, as well as considerations when combining TUS with neuroimaging, electrophysiology, or other brain stimulation techniques. We hope that this practical guide to TUS will assist both novice and experienced users in planning and conducting high-quality studies and provide a solid foundation for further advancements in this promising field.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
