Publications by authors named "Victor H Souza"

8 Publications

  • Page 1 of 1

Multi-locus transcranial magnetic stimulation system for electronically targeted brain stimulation.

Brain Stimul 2021 Nov 21;15(1):116-124. Epub 2021 Nov 21.

Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland; BioMag Laboratory, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.

Background: Transcranial magnetic stimulation (TMS) allows non-invasive stimulation of the cortex. In multi-locus TMS (mTMS), the stimulating electric field (E-field) is controlled electronically without coil movement by adjusting currents in the coils of a transducer.

Objective: To develop an mTMS system that allows adjusting the location and orientation of the E-field maximum within a cortical region.

Methods: We designed and manufactured a planar 5-coil mTMS transducer to allow controlling the maximum of the induced E-field within a cortical region approximately 30 mm in diameter. We developed electronics with a design consisting of independently controlled H-bridge circuits to drive up to six TMS coils. To control the hardware, we programmed software that runs on a field-programmable gate array and a computer. To induce the desired E-field in the cortex, we developed an optimization method to calculate the currents needed in the coils. We characterized the mTMS system and conducted a proof-of-concept motor-mapping experiment on a healthy volunteer. In the motor mapping, we kept the transducer placement fixed while electronically shifting the E-field maximum on the precentral gyrus and measuring electromyography from the contralateral hand.

Results: The transducer consists of an oval coil, two figure-of-eight coils, and two four-leaf-clover coils stacked on top of each other. The technical characterization indicated that the mTMS system performs as designed. The measured motor evoked potential amplitudes varied consistently as a function of the location of the E-field maximum.

Conclusion: The developed mTMS system enables electronically targeted brain stimulation within a cortical region.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.brs.2021.11.014DOI Listing
November 2021

Trade-off between stimulation focality and the number of coils in multi-locus transcranial magnetic stimulation.

J Neural Eng 2021 Nov 12;18(6). Epub 2021 Nov 12.

Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland.

. Coils designed for transcranial magnetic stimulation (TMS) must incorporate trade-offs between the required electrical power or energy, focality and depth penetration of the induced electric field (E-field), coil size, and mechanical properties of the coil, as all of them cannot be optimally met at the same time. In multi-locus TMS (mTMS), a transducer consisting of several coils allows electronically targeted stimulation of the cortex without physically moving a coil. In this study, we aimed to investigate the relationship between the number of coils in an mTMS transducer, the focality of the induced E-field, and the extent of the cortical region within which the location and orientation of the maximum of the induced E-field can be controlled.We applied convex optimization to design planar and spherically curved mTMS transducers of different E-field focalities and analyzed their properties. We characterized the trade-off between the focality of the induced E-field and the extent of the cortical region that can be stimulated with an mTMS transducer with a given number of coils.At the expense of the E-field focality, one can, with the same number of coils, design an mTMS transducer that can control the location and orientation of the peak of the induced E-field within a wider cortical region.. With E-fields of moderate focality, the problem of electronically targeted TMS becomes considerably easier compared with highly focal E-fields; this may speed up the development of mTMS and the emergence of new clinical and research applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1741-2552/ac3207DOI Listing
November 2021

Effect of stimulus orientation and intensity on short-interval intracortical inhibition (SICI) and facilitation (SICF): A multi-channel transcranial magnetic stimulation study.

PLoS One 2021 22;16(9):e0257554. Epub 2021 Sep 22.

Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland.

Besides stimulus intensities and interstimulus intervals (ISI), the electric field (E-field) orientation is known to affect both short-interval intracortical inhibition (SICI) and facilitation (SICF) in paired-pulse transcranial magnetic stimulation (TMS). However, it has yet to be established how distinct orientations of the conditioning (CS) and test stimuli (TS) affect the SICI and SICF generation. With the use of a multi-channel TMS transducer that provides electronic control of the stimulus orientation and intensity, we aimed to investigate how changes in the CS and TS orientation affect the strength of SICI and SICF. We hypothesized that the CS orientation would play a major role for SICF than for SICI, whereas the CS intensity would be more critical for SICI than for SICF. In eight healthy subjects, we tested two ISIs (1.5 and 2.7 ms), two CS and TS orientations (anteromedial (AM) and posteromedial (PM)), and four CS intensities (50, 70, 90, and 110% of the resting motor threshold (RMT)). The TS intensity was fixed at 110% RMT. The intensities were adjusted to the corresponding RMT in the AM and PM orientations. SICI and SICF were observed in all tested CS and TS orientations. SICI depended on the CS intensity in a U-shaped manner in any combination of the CS and TS orientations. With 70% and 90% RMT CS intensities, stronger PM-oriented CS induced stronger inhibition than weaker AM-oriented CS. Similar SICF was observed for any CS orientation. Neither SICI nor SICF depended on the TS orientation. We demonstrated that SICI and SICF could be elicited by the CS perpendicular to the TS, which indicates that these stimuli affected either overlapping or strongly connected neuronal populations. We concluded that SICI is primarily sensitive to the CS intensity and that CS intensity adjustment resulted in similar SICF for different CS orientations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0257554PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8457500PMC
November 2021

HLA-A, -B, -DRB1, -DQA1, and -DQB1 profile in a population from southern Brazil.

HLA 2018 11;92(5):298-303

Laboratory of Immunogenetics, Department of Basic Health Sciences, State University of Maringá, Paraná, Brazil.

The aim of this study was to determine the allele and haplotype frequencies of HLA-A, -B, -DRB1, and -DQB1 in a self-declared White population from the north and northwestern state of Paraná, southern Brazil, and compare the data with populations worldwide. The genotyping was performed with a group of 641 individuals, based on PCR-SSO and -SSP methods, and allele and haplotype frequencies were estimated. Comparisons with European, African, Asian, and Amerindian populations were performed. The most frequent allelic groups, alleles and haplotypes were: HLA-A*02, HLA-B*35, HLA-DRB1*07:01, HLA-DQB1*03:01, and HLA-A*01/B*08/DRB1*03:01. The results reinforced a predominance of a European composition in the self-declared White population from the north and northwestern Paraná.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/tan.13368DOI Listing
November 2018

Can the Recording of Motor Potentials Evoked by Transcranial Magnetic Stimulation Be Optimized?

Front Hum Neurosci 2017 15;11:413. Epub 2017 Aug 15.

Laboratório de Neurobiologia II, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de JaneiroRio de Janeiro, Brazil.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fnhum.2017.00413DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5559546PMC
August 2017

Conducting, transparent and flexible substrates obtained from interfacial thin films of double-walled carbon nanotubes.

J Colloid Interface Sci 2017 Sep 28;502:146-152. Epub 2017 Apr 28.

Departamento de Química, Universidade Federal do Paraná (UFPR), CP 19081, CEP 81531-990, Curitiba, Paraná, Brazil. Electronic address:

Conducting and transparent interfacial thin films have been prepared from double-walled carbon nanotubes (DWCNT) and further deposited over glass and plastic (polyethylene terephtalate-PET) substrates. The morphology, vibrational structure as well as the optical and electrical properties have been evaluated. The influence of the DWCNT purifying treatment, the amount of carbon nanotubes used to prepare the thin films, and the annealing of the films at different temperatures has been evaluated to optimize both electrical and optical properties. Values of sheet resistance ranging from 0.53 to 27.8 kΩ □ and transmittance at 550nm from 59 to 90% have been achieved. Similar behavior obtained for films deposited on PET or glass substrates indicate a good reproducibility of the method, besides the high potential for further applications on flexible devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jcis.2017.04.084DOI Listing
September 2017

Carbon nanotube/Prussian blue thin films as cathodes for flexible, transparent and ITO-free potassium secondary battery.

J Colloid Interface Sci 2016 Sep 28;478:107-16. Epub 2016 May 28.

Department of Chemistry, Federal University of Paraná (UFPR), CP 19083, CEP 81531-980, Curitiba, PR, Brazil. Electronic address:

Thin films of either unpurified single-walled carbon nanotubes (SWCNT) or iron-filled multi-walled carbon nanotubes (MWCNT) were deposited through the liquid-liquid interfacial route over plastic substrates, yielding transparent, flexible and ITO-free electrodes. The iron species presented in both electrodes (inside of the MWCNT cavities or outside of the SWCNT bundles, related to the catalyst remaining of the growth process) were employed as reactant to the electrosynthesis of Prussian blue (PB), yielding carbon nanotubes/Prussian blue nanocomposite thin films, which were characterized by Raman spectroscopy, scanning electron microscopy, atomic force microscopy, cyclic voltammetry and galvanostatic charge/discharge measurements. The nanocomposite films were employed as cathodes for flexible, transparent and ITO-free potassium batteries, showing reversible charge/discharge behavior and specific capacitance of 8.3mAhcm(-3) and 2.7mAhcm(-3) for SWCNT/PB and MWCNT/PB, respectively.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jcis.2016.05.056DOI Listing
September 2016

Graphene/nickel nanoparticles composites from graphenide solutions.

J Colloid Interface Sci 2015 Sep 30;453:28-35. Epub 2015 Apr 30.

Departamento de Química, Universidade Federal do Paraná (UFPR), CP 19081, CEP 81531-990, Curitiba, PR, Brazil. Electronic address:

Nanocomposites between nickel nanoparticles and graphene were obtained starting from nickel cations and graphenide solutions (negatively charged graphene layers) as both reducing agent to nickel cations and graphene source. Different nanomaterials were obtained in two different solvents, N-methyl-2-pyrrolidone (NMP) and tetrahydrofuran (THF), with different nickel/graphene ratios. The nanomaterials were characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). All the samples consist of large graphene layers highly decorated with crystalline nickel nanoparticles, of size ranging from 2 to 10 nm. Thin films of the samples were deposited on indium-tin oxide (ITO) substrates and electrochemically characterized in alkaline medium, leading to Ni(OH)2/NiOOH redox pair, where the increase of the nickel proportion in the nanocomposites resulted in higher peak currents. The samples obtained in NMP showed the best performance with a fivefold increase of the peak currents, consistent with the lower charge transfer resistance as seen by electrochemical impedance spectroscopy (EIS).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jcis.2015.04.036DOI Listing
September 2015
-->