Efficient high-resolution TMS mapping of the human motor cortex by nonlinear regression

AbstractBackgroundThe precise cortical origins of the electrophysiological and behavioral effects of transcranial magnetic stimulation (TMS) remain largely unclear. Addressing this question is further impeded by substantial inter-individual response variability to TMS.ObjectiveWe present a novel method to reliably and user-independently determine the effectively stimulated cortical site at the individual subject level. This generic approach combines physiological measurements with electric field simulations and leverages information from random coil positions, electric field estimations, and electromyography.MethodsWe applied ~1000 single biphasic TMS pulses with standard TMS hardware to 13 subjects with random coil positions & orientations over the primary motor hand area. Motor evoked potentials (MEPs) of three finger muscles were recorded concurrently. We calculated the corresponding electric fields for all TMS pulses and regressed them against the elicited MEPs in each cortical element. This yields a cortical map of congruency between induced field strength and generated response.ResultsWe observed high congruence between the electric fields and the elicited MEPs in hotspots located primarily on the crowns and rims of the precentral gyrus. The three cortical digit representations could be distinguished at the individual subject level with a high spatial resolution. A post-hoc convergence analysis revealed a possible lower bound of only 180 pulses to obtain qualitatively identical results.ConclusionsLeveraging information from many different TMS pulses significantly reduces the number of necessary stimulations and mapping time. The protocol is easy to implement due to the realization of arbitrary coil positions & orientations and is suitable for practical and clinical use such as preoperative mapping.

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A novel approach to localize cortical TMS effects

10.1101/595603 ◽

2019 ◽

Cited By ~ 1

Author(s):

Konstantin Weise ◽

Ole Numssen ◽

Axel Thielscher ◽

Gesa Hartwigsen ◽

Thomas R. Knösche

Keyword(s):

Electric Fields ◽

Motor Evoked Potentials ◽

Tangential Component ◽

Sensitivity Analyses ◽

Model Parameters ◽

Language Mapping ◽

Individual Subject ◽

Novel Approach ◽

Critical Model ◽

The Individual

ABSTRACTDespite the widespread use of transcranial magnetic stimulation (TMS), the precise cortical location underlying the physiological and behavioral stimulation effects are still only coarsely known. So far, mapping strategies rely on center of gravity approaches and therefore localize the stimulated cortical site only approximately and indirectly. Focusing on the motor cortex, we present a novel method to reliably determine the effectively stimulated cortical site at the individual subject level. The approach combines measurements of motor evoked potentials (MEPs) at different coil positions and orientations with numerical modeling of induced electric fields. We identify sharply bounded cortical areas around the gyral crowns and rims of the motor hand area as the origin of MEPs and show that the tangential component and the magnitude of the electric field is most relevant for the observed effect. To validate our approach, we determined motor thresholds for coil positions and orientations for the predicted cortical target. Our methods allows for the identification of optimal coil positions and orientations. Moreover, we used extensive uncertainty and sensitivity analyses to verify the robustness of the method and identify the most critical model parameters. Our generic approach improves the localization of the cortex area stimulated by TMS and may be transferred to other modalities such as language mapping.

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Decoding individualized motor cortical excitability states from whole-brain electroencephalography

10.1101/2021.10.22.465447 ◽

2021 ◽

Author(s):

Sara J Hussain ◽

Romain Quentin

Keyword(s):

Cortical Excitability ◽

Motor Evoked Potentials ◽

Brain State ◽

Individual Subject ◽

Whole Brain ◽

State Dependent ◽

Subject Specific ◽

The Individual ◽

Real Time Identification ◽

The Right

OBJECTIVE: Brain state-dependent transcranial magnetic stimulation (TMS) requires real-time identification of cortical excitability states. Here, we aimed to identify individualized, subject-specific motor cortex (M1) excitability states from whole-scalp electroencephalography (EEG) signals. METHODS: We analyzed a pre-existing dataset that delivered 600 single TMS pulses to the right M1 during EEG and electromyography (EMG) recordings. Subject-specific multivariate pattern classification was used to discriminate between brain states during which TMS elicited small or large motor-evoked potentials (MEPs). RESULTS: Classifiers trained at the individual subject level successfully discriminated between low and high M1 excitability states. MEPs elicited during classifier-predicted high excitability states were significantly larger than those elicited during classifier-predicted low excitability states. Classifiers trained on subject-specific data obtained immediately before TMS delivery performed better than classifiers trained on data from earlier time points, and subject-specific classifiers generalized weakly but significantly across subjects. CONCLUSION: Decoding individualized M1 excitability states from whole-brain EEG activity is feasible and robust. SIGNIFICANCE: Deploying subject-specific classifiers during brain state-dependent TMS may enable effective, fully individualized neuromodulation in the future.

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Multifocal tDCS modulates resting-state functional connectivity in older adults depending on induced electric field and baseline connectivity

10.1101/2020.05.15.090860 ◽

2020 ◽

Author(s):

Kilian Abellaneda-Pérez ◽

Lídia Vaqué-Alcázar ◽

Ruben Perellón-Alfonso ◽

Cristina Solé-Padullés ◽

Núria Bargalló ◽

...

Keyword(s):

Older Adults ◽

Electric Field ◽

Electric Fields ◽

Resting State ◽

Element Model ◽

Individual Variability ◽

Neural Dynamics ◽

Resting State Functional Connectivity ◽

The Individual ◽

Resting State Connectivity

AbstractBackgroundAdvancing age affects the brain’s resting-state functional networks. Combining non-invasive brain stimulation (NIBS) with neuroimaging is a promising approach to modulate activity across resting-state functional systems and explore their true contribution to cognitive function in aging. However, substantial individual variability in the response to NIBS has been reported and, hence, identifying the individual predictors of NIBS-induced modulatory effects is crucial if we are to harness their potential.MethodsThirty-one cognitively healthy older adults (71.68 ± 2.5 years; 19 females) underwent two different multifocal real tDCS conditions (C1 and C2) and a sham condition in a crossover design during a resting-state functional magnetic resonance imaging (rs-fMRI) acquisition. The real tDCS conditions were designed to induce two distinct electric field distribution patterns either targeting generalized cortical overactivity or a dissociation between the frontal areas and the posteromedial cortex. Stimulation was delivered through an MRI-compatible device using 8 small circular electrodes. Each individuals’ anatomical T1-weighted MRI was used to generate a finite element model to define the individual electric field generated by each tDCS condition.ResultsThe two tDCS conditions modulated resting-state connectivity differently. C1 increased the coactivation of numerous functional couplings as compared to sham, however, a smaller amount of connections increased in C1 as compared to C2, while no differences between C2 and sham were appreciated. At the group level, C1-induced modulations primarily included temporo-occipital areas and distinct cerebellar regions. This functional pattern was anatomically consistent with the estimated distribution of the induced electric field in the C1 condition. Finally, at the individual level, the extent of tDCS-induced rs-fMRI modulation in C1 was predicted by baseline resting-state connectivity and simulation-based electric field magnitude.DiscussionOur results highlighted that multifocal tDCS procedures can effectively change neural dynamics in the elderly consistently with the spatial distribution of the estimated electric fields on the brain. Furthermore, we showed that specific brain factors that have been revealed to explain part of the individual variability to NIBS in young samples are also relevant in older adults. In accordance, designing multifocal tDCS configurations based on specific fMRI patterns appears to be a valuable approach to precisely adjust those complex neural dynamics sustaining cognition that are affected as a function of age. Furthermore, these innovative NIBS-based interventions should be individually-tailored based on subject-specific structural and functional data to ultimately boost their potential in aged populations.

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A within-subjects comparison of the acquisition of quantity-related inferences

Proceedings of the Linguistic Society of America ◽

10.3765/plsa.v5i1.4731 ◽

2020 ◽

Vol 5 (1) ◽

pp. 558

Author(s):

Alicia Parrish ◽

Ailís Cournane

Keyword(s):

Judgment Task ◽

Individual Response ◽

Scalar Implicature ◽

Response Patterns ◽

Rating Task ◽

Scalar Implicatures ◽

Individual Subject ◽

Value Judgment ◽

Within Subjects ◽

The Individual

This study directly compares quantity inferences from scalar implicatures (‘Some of the ducks are black’) and uniqueness presuppositions in deﬁnites (‘the duck is black’) to exhaustivity inferences in English it-clefts (‘It’s the duck that’s black’) for which the theoretical literature disagrees on the source of inference – pragmatic (like scalar implicatures), or semantic (like presuppositions). We investigate whether within-subjects correlations in acquisition can inform us about the source of exhaustivity inferences. Assuming comprehension is achieved once the necessary basis for meaning is acquired, it-clefts should pattern with presupposition judgments if computing a presupposition is involved and should pattern with scalar implicature judgments if computing an implicature is involved. We conduct three experiments to test how closely it-cleft judgments pattern with other quantityrelated inferences, keeping materials maximally similar. The ﬁrst two experiments test adult participants using a Truth Value Judgment Task and then a 3-point Rating Task; we ﬁnd that adults’ response patterns to under-informative uses of these constructions differ both across individuals and across inference types, with the Rating Task giving more informative results. In the third experiment, we use the 3-point Rating Task with 4-, 5-, and 6- year olds to characterize response patterns across the three inference types for each individual subject. We ﬁnd that the individual response patterns children exhibit are consistent with the theory that it-cleft exhaustivity shares an underlying cognitive source with the computation of presupposition inferences, but not with scalar implicature inferences.

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Electric field dependent effects of motor cortical TDCS

10.1101/327361 ◽

2018 ◽

Author(s):

Ilkka Laakso ◽

Marko Mikkonen ◽

Soichiro Koyama ◽

Daisuke Ito ◽

Tomofumi Yamaguchi ◽

...

Keyword(s):

Electric Field ◽

Electric Fields ◽

Primary Motor Cortex ◽

Cortical Excitability ◽

Brain Anatomy ◽

After Effects ◽

Neuropsychiatric Diseases ◽

Motor Cortical ◽

The Individual ◽

The Brain

AbstractTranscranial direct current stimulation (TDCS) can modulate motor cortical excitability. However, its after-effects are highly variable between individuals. Individual cranial and brain anatomy may contribute to this variability by producing varying electric fields in each subject’s brain. Here we show that these fields are related to excitability changes following anodal TDCS of the primary motor cortex (M1). We found in two experiments (N=28 and N=9) that the after-effects of TDCS were proportional to the individual electric field in M1, calculated using MRI-based models. Individuals with the lowest and highest local electric fields in M1 tended to produce opposite changes in excitability. Furthermore, the effect was field-direction dependent and non-linear with stimulation duration or other experimental parameters. The electric field component pointing into the brain was negatively proportional to the excitability changes following 1 mA 20 min TDCS of right M1 (N=28); the effect was opposite after 1 mA 10 min TDCS of left M1 (N=9). Our results demonstrate that a large part of variability in the after-effects of motor cortical TDCS is due to inter-individual differences in the electric fields. We anticipate that individualized electric field dosimetry could be used to control the neuroplastic effects of TDCS, which is increasingly being explored as a treatment for various neuropsychiatric diseases.

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Tuning the Electric Field Response of MOFs by Rotatable Dipolar Linkers

10.26434/chemrxiv.8153198.v1 ◽

2019 ◽

Author(s):

Johannes P. Dürholt ◽

Babak Farhadi Jahromi ◽

Rochus Schmid

Keyword(s):

Electric Field ◽

Electric Fields ◽

Structural Changes ◽

Dielectric Behavior ◽

Two Dimensions ◽

Dielectric Constants ◽

Electric Response ◽

Dipole Strength ◽

Metal Organic ◽

Dynamics Simulations

Recently the possibility of using electric fields as a further stimulus to trigger structural changes in metal-organic frameworks (MOFs) has been investigated. In general, rotatable groups or other types of mechanical motion can be driven by electric fields. In this study we demonstrate how the electric response of MOFs can be tuned by adding rotatable dipolar linkers, generating a material that exhibits paralectric behavior in two dimensions and dielectric behavior in one dimension. The suitability of four different methods to compute the relative permittivity κ by means of molecular dynamics simulations was validated. The dependency of the permittivity on temperature T and dipole strength μ was determined. It was found that the herein investigated systems exhibit a high degree of tunability and substantially larger dielectric constants as expected for MOFs in general. The temperature dependency of κ obeys the Curie-Weiss law. In addition, the influence of dipolar linkers on the electric field induced breathing behavior was investigated. With increasing dipole moment, lower field strength are required to trigger the contraction. These investigations set the stage for an application of such systems as dielectric sensors, order-disorder ferroelectrics or any scenario where movable dipolar fragments respond to external electric fields.

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Stasis Anxiety

10.1093/oso/9780198793762.003.0007 ◽

2017 ◽

Author(s):

Andrew van der Vlies

Keyword(s):

South Africa ◽

Civil War ◽

Black Writers ◽

Political Rights ◽

Ancient Greek ◽

Individual Subject ◽

Starting Point ◽

The Individual ◽

Past Experiences ◽

Contemporary Writing

Two recent debut novels, Songeziwe Mahlangu’s Penumbra (2013) and Masande Ntshanga’s The Reactive (2014), reflect the experience of impasse, stasis, and arrested development experienced by many in South Africa. This chapter uses these novels as the starting point for a discussion of writing by young black writers in general, and as representative examples of the treatment of ‘waithood’ in contemporary writing. It considers (spatial and temporal) theorisations of anxiety, discerns recursive investments in past experiences of hope (invoking Jennifer Wenzel’s work to consider the afterlives of anti-colonial prophecy), assesses the usefulness of Giorgio Agamben’s elaboration of the ancient Greek understanding of stasis as civil war, and asks how these works’ elaboration of stasis might be understood in relation to Wendy Brown’s discussion of the eclipsing of the individual subject of political rights by the neoliberal subject whose very life is framed by its potential to be understood as capital.

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Meta-Deflectors Made of Dielectric Nanohole Arrays with Anti-Damage Potential

Photonics ◽

10.3390/photonics8040107 ◽

2021 ◽

Vol 8 (4) ◽

pp. 107

Author(s):

Haichao Yu ◽

Feng Tang ◽

Jingjun Wu ◽

Zao Yi ◽

Xin Ye ◽

...

Keyword(s):

Electric Field ◽

Electric Fields ◽

Laser Cutting ◽

High Complexity ◽

Damage Potential ◽

Optical Components ◽

Nanohole Arrays ◽

Intense Light ◽

Polarization Of Light ◽

Air Hole

In intense-light systems, the traditional discrete optical components lead to high complexity and high cost. Metasurfaces, which have received increasing attention due to the ability to locally manipulate the amplitude, phase, and polarization of light, are promising for addressing this issue. In the study, a metasurface-based reflective deflector is investigated which is composed of silicon nanohole arrays that confine the strongest electric field in the air zone. Subsequently, the in-air electric field does not interact with the silicon material directly, attenuating the optothermal effect that causes laser damage. The highest reflectance of nanoholes can be above 99% while the strongest electric fields are tuned into the air zone. One presentative deflector is designed based on these nanoholes with in-air-hole field confinement and anti-damage potential. The 1st order of the meta-deflector has the highest reflectance of 55.74%, and the reflectance sum of all the orders of the meta-deflector is 92.38%. The optothermal simulations show that the meta-deflector can theoretically handle a maximum laser density of 0.24 W/µm2. The study provides an approach to improving the anti-damage property of the reflective phase-control metasurfaces for intense-light systems, which can be exploited in many applications, such as laser scalpels, laser cutting devices, etc.

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Integrating flexible electronics for pulsed electric field delivery in a vascularized 3D glioblastoma model

npj Flexible Electronics ◽

10.1038/s41528-021-00115-x ◽

2021 ◽

Vol 5 (1) ◽

Author(s):

Marie C. Lefevre ◽

Gerwin Dijk ◽

Attila Kaszas ◽

Martin Baca ◽

David Moreau ◽

...

Keyword(s):

Electric Field ◽

Electric Fields ◽

Flexible Electronics ◽

Soft Tissues ◽

Multiphoton Microscopy ◽

Membrane Integrity ◽

Tumor Model ◽

Pulsed Electric Fields ◽

In Ovo ◽

Cell Membrane Integrity

AbstractGlioblastoma is a highly aggressive brain tumor, very invasive and thus difficult to eradicate with standard oncology therapies. Bioelectric treatments based on pulsed electric fields have proven to be a successful method to treat cancerous tissues. However, they rely on stiff electrodes, which cause acute and chronic injuries, especially in soft tissues like the brain. Here we demonstrate the feasibility of delivering pulsed electric fields with flexible electronics using an in ovo vascularized tumor model. We show with fluorescence widefield and multiphoton microscopy that pulsed electric fields induce vasoconstriction of blood vessels and evoke calcium signals in vascularized glioblastoma spheroids stably expressing a genetically encoded fluorescence reporter. Simulations of the electric field delivery are compared with the measured influence of electric field effects on cell membrane integrity in exposed tumor cells. Our results confirm the feasibility of flexible electronics as a means of delivering intense pulsed electric fields to tumors in an intravital 3D vascularized model of human glioblastoma.

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Electro-Optic Control of Lithium Niobate Bulk Whispering Gallery Resonators: Analysis of the Distribution of Externally Applied Electric Fields

Crystals ◽

10.3390/cryst11030298 ◽

2021 ◽

Vol 11 (3) ◽

pp. 298

Author(s):

Yannick Minet ◽

Hans Zappe ◽

Ingo Breunig ◽

Karsten Buse

Keyword(s):

Lithium Niobate ◽

Electric Field ◽

Electric Fields ◽

Frequency Comb ◽

Parametric Oscillation ◽

Pockels Effect ◽

Optical Mode ◽

Cylindrical Resonator ◽

Whispering Gallery ◽

Electro Optic

Whispering gallery resonators made out of lithium niobate allow for optical parametric oscillation and frequency comb generation employing the outstanding second-order nonlinear-optical properties of this material. An important knob to tune and control these processes is, e.g., the linear electro-optic effect, the Pockels effect via externally applied electric fields. Due to the shape of the resonators a precise prediction of the electric field strength that affects the optical mode is non-trivial. Here, we study the average strength of the electric field in z-direction in the region of the optical mode for different configurations and geometries of lithium niobate whispering gallery resonators with the help of the finite element method. We find that in some configurations almost 100% is present in the cavity compared to the ideal case of a cylindrical resonator. Even in the case of a few-mode resonator with a very thin rim we find a strength of 90%. Our results give useful design considerations for future arrangements that may benefit from the strong electro-optic effect in bulk whispering gallery resonators made out of lithium niobate.

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