Biology subjects

Dannhauer, M.

Publications and source records attributed to Dannhauer, M..

3 recordsLinked to original sources

bioRxiv2019

Site-specific effects of online rTMS during a working memory task in healthy older adults.

The process of manipulating information within working memory (WM) is central to many cognitive functions, but also declines rapidly in old age. Given the importance of WM manipulation for maintaining healthy cognition, improving this process could markedly enhance health-span in older adults. The current pre-registered study tested the potential of online repetitive transcranial magnetic stimulation (rTMS) to enhance WM manipulation in healthy elderly adults. Online 5Hz rTMS was applied over the left lateral parietal cortex of 15 subjects to test the hypothesis that active rTMS would significantly improve performance compared to sham stimulation, and that these effects would be most pronounced in conditions with the highest cognitive demand. rTMS was applied while participants performed a delayed-response alphabetization task with two individually-titrated levels of difficulty. Sham stimulation was applied using an electrical sham coil that produced similar clicking sounds and somatosensory sensation as active stimulation but induced negligible effects on the brain. A stimulation site in left lateral parietal cortex was identified from fMRI activation maps and was targeted using individualized electric field modeling, stereotactic neuronavigation, and real-time robotic positioning, allowing optimal coil placement during the stimulation. Contrary to the a priori hypothesis, active rTMS significantly decreased accuracy relative to sham, and only in the hardest difficulty level. These results, therefore, demonstrate engagement of cortical WM processing, but not the anticipated facilitation, and provide a prescription for future studies that may attempt to enhance memory through application of different stimulation parameters.\n\nHighlightsO_LIThis study is one of the first attempts to enhance WM manipulation with online rTMS\nC_LIO_LIOnline 5Hz rTMS and sham were applied over the left parietal cortex of older adults\nC_LIO_LIIndividualized fMRI and electric field modeling were used to optimize targeting\nC_LIO_LIContrary to expectations, rTMS disrupted working memory manipulation abilities\nC_LIO_LIThis demonstrates that parietal cortex is involved in WM and modifiable with rTMS\nC_LI

neuroscience↗

bioRxiv2019

Transcranial Alternating Current Stimulation (tACS) Entrains Alpha Oscillations by Preferential Phase Synchronization of Fast-Spiking Cortical Neurons to Stimulation Waveform

Modeling studies predict that transcranial alternating current stimulation (tACS) entrains brain oscillations, yet direct examination has been lacking or potentially contaminated by stimulation artefact. Here we first demonstrate how the posterior parietal cortex drives primary visual cortex and thalamic LP in the alpha-band in head-fixed awake ferrets. The spike-field synchrony is maximum within alpha frequency, and more prominent for narrow-spiking neurons than broad-spiking ones. Guided by a validated model of electric field distribution, we produced electric fields comparable to those in humans and primates (< 0.5 mV/mm). We found evidence to support the model-driven predictions of how tACS entrains neural oscillations as explained by the triangular Arnold tongue pattern. In agreement with the stronger spike-field coupling of narrow-spiking cells, tACS more strongly entrained this cell population. Our findings provide the first in vivo evidence of how tACS with electric field amplitudes used in human studies entrains neuronal oscillators.

neuroscience↗

bioRxiv2018

Conditions for numerically accurate TMS electric field simulation

BackgroundComputational simulations of the E-field induced by transcranial magnetic stimulation (TMS) are increasingly used to understand its mechanisms and to inform its administration. However, characterization of the accuracy of the simulation methods and the factors that affect it is lacking.\n\nObjectiveTo ensure the accuracy of TMS E-field simulations, we systematically quantify their numerical error and provide guidelines for their setup.\n\nMethodWe benchmark the accuracy of computational approaches that are commonly used for TMS E-field simulations, including the finite element method (FEM), boundary element method (BEM), finite difference method (FDM), and coil modeling methods.\n\nResultsTo achieve cortical E-field error levels below 2%, the commonly used FDM and 1st order FEM require meshes with an average edge length below 0.4 mm, whereas BEM and 2nd (or higher) order FEM require edge lengths below 1.5 mm, which is more practical. Coil models employing magnetic and current dipoles require at least 200 and 3,000 dipoles, respectively. For thick solid-conductor coils and frequencies above 3 kHz, winding eddy currents may have to be modeled.\n\nConclusionBEM, FDM, and FEM methods converge to the same solution. However, FDM and 1st order FEM converge slowly with increasing mesh resolution; therefore, the use of BEM or 2nd (or higher) order FEM is recommended. In some cases, coil eddy currents must be modeled. Both electric current dipole and magnetic dipole models of the coil current can be accurate with sufficiently fine discretization.\n\nFundingResearch reported in this publication was supported by the National Institute of Mental Health and the National Institute of Neurological Disorders and Stroke of the National Institutes of Health under Award Numbers RF1MH114268 and R01NS088674-S1. The content of current research is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.\n\nHIGHLIGHTSO_LIFDM and 1st order FEM with 1.5 mm average mesh edge length have numerical errors above 7%.\nC_LIO_LIBEM or 2nd order FEM are most efficient for achieving numerical errors < 2%.\nC_LIO_LICoil wire cross-section must be accounted to achieve E-field errors below < 2%.\nC_LIO_LICoil eddy currents can account for > 2% of E-field when very brief pulses are used.\nC_LI

bioengineering↗