High definition tDCS effect on postural control in healthy individuals: Entropy analysis of a crossover clinical trial

Objective: Converging evidence supporting an effect of transcranial direct current stimulation (tDCS) on postural control and human verticality perception highlights this strategy as promising for post-stroke rehabilitation. We have previously demonstrated polarity-dependent effects of high-definition tDCS (HD-tDCS) on weight-bearing asymmetry. However, there is no investigation regarding the time-course of effects on postural control induced by HD-tDCS protocols. Thus, we performed a nonlinear time series analysis focusing on the entropy of the ground reaction force as a secondary investigation of our randomized, double-blind, placebo-controlled, crossover clinical trial. Materials and Methods: Twenty healthy right-handed young adults received the following conditions (random order, separate days); anode center HD-tDCS, cathode center HD-tDCS or sham HD-tDCS at 1, 2, and 3 mA over the right temporo-parietal junction (TPJ). Using summarized time series of transfer entropy, we evaluated the exchanging information (causal direction) between both force plates and compared the dose-response across the healthy subjects with a Generalized Linear Hierarchical/Mixed Model (GLMM). Results: We found significant variation during the dynamic information flow (p \u3c 0.001) among the dominant bodyside (and across time). A greater force transfer entropy was observed from the right to the left side during the cathode-center HD-tDCS up to 2 mA, with a causal relationship in the information flow (equilibrium force transfer) from right to left that decreased over time. Conclusions: HD-tDCS intervention induced a dynamic influence over time on postural control entropy. Right hemisphere TPJ stimulation using cathode-center HD-tDCS can induce an asymmetry of body weight distribution towards the ipsilateral side of stimulation. These results support the clinical potential of HD-tDCS for post-stroke rehabilitation

Manipulation of human verticality using high-definition transcranial direct current stimulation

Background: Using conventional tDCS over the temporo-parietal junction (TPJ) we previously reported that it is possible to manipulate subjective visual vertical (SVV) and postural control. We also demonstrated that high-definition tDCS (HD-tDCS) can achieve substantially greater cortical stimulation focality than conventional tDCS. However, it is critical to establish dose-response effects using well-defined protocols with relevance to clinically meaningful applications. Objective: To conduct three pilot studies investigating polarity and intensity-dependent effects of HD-tDCS over the right TPJ on behavioral and physiological outcome measures in healthy subjects. We additionally aimed to establish the feasibility, safety, and tolerability of this stimulation protocol. Methods: We designed three separate randomized, double-blind, crossover phase I clinical trials in different cohorts of healthy adults using the same stimulation protocol. The primary outcome measure for trial 1 was SVV; trial 2, weight-bearing asymmetry (WBA); and trial 3, electroencephalography power spectral density (EEG-PSD). The HD-tDCS montage comprised a single central, and 3 surround electrodes (HD-tDCS3x1) over the right TPJ. For each study, we tested 3x2 min HD-tDCS3x1 at 1, 2 and 3 mA; with anode center, cathode center, or sham stimulation, in random order across days. Results: We found significant SVV deviation relative to baseline, specific to the cathode center condition, with consistent direction and increasing with stimulation intensity. We further showed significant WBA with direction governed by stimulation polarity (cathode center, left asymmetry; anode center, right asymmetry). EEG-PSD in the gamma band was significantly increased at 3 mA under the cathode. Conclusions: The present series of studies provide converging evidence for focal neuromodulation that can modify physiology and have behavioral consequences with clinical potential

Polarity-Dependent Misperception of Subjective Visual Vertical during and after Transcranial Direct Current Stimulation (tDCS)

Pathologic tilt of subjective visual vertical (SVV) frequently has adverse functional consequences for patients with stroke and vestibular disorders. Repetitive transcranial magnetic stimulation (rTMS) of the supramarginal gyrus can produce a transitory tilt on SVV in healthy subjects. However, the effect of transcranial direct current stimulation (tDCS) on SVV has never been systematically studied. We investigated whether bilateral tDCS over the temporal- parietal region could result in both online and offline SVV misperception in healthy subjects. In a randomized, sham-controlled, single-blind crossover pilot study, thirteen healthy subjects performed tests of SVV before, during and after the tDCS applied over the temporal- parietal region in three conditions used on different days: right anode/left cathode; right cathode/left anode; and sham. Subjects were blind to the tDCS conditions. Montage-specific current flow patterns were investigated using computational models. SVV was significantly displaced towards the anode during both active stimulation conditions when compared to sham condition. Immediately after both active conditions, there were rebound effects. Longer lasting after-effects towards the anode occurred only in the right cathode/left anode condition. Current flow models predicted the stimulation of temporal-parietal regions under the electrodes and deep clusters in the posterior limb of the internal capsule. The present findings indicate that tDCS over the temporal-parietal region can significantly alter human SVV perception. This tDCS approach may be a potential clinical tool for the treatment of SVV misperception in neurological patients

High Definition tDCS Effect on Postural Control in Healthy Individuals: Entropy Analysis of a Crossover Clinical Trial

Objective: Converging evidence supporting an effect of transcranial direct current stimulation (tDCS) on postural control and human verticality perception highlights this strategy as promising for post-stroke rehabilitation. We have previously demonstrated polarity-dependent effects of high-definition tDCS (HD-tDCS) on weight-bearing asymmetry. However, there is no investigation regarding the time-course of effects on postural control induced by HD-tDCS protocols. Thus, we performed a nonlinear time series analysis focusing on the entropy of the ground reaction force as a secondary investigation of our randomized, double-blind, placebo-controlled, crossover clinical trial. Materials and Methods: Twenty healthy right-handed young adults received the following conditions (random order, separate days); anode center HD-tDCS, cathode center HD-tDCS or sham HD-tDCS at 1, 2, and 3 mA over the right temporo-parietal junction (TPJ). Using summarized time series of transfer entropy, we evaluated the exchanging information (causal direction) between both force plates and compared the dose-response across the healthy subjects with a Generalized Linear Hierarchical/Mixed Model (GLMM). Results: We found significant variation during the dynamic information flow (p < 0.001) among the dominant bodyside (and across time). A greater force transfer entropy was observed from the right to the left side during the cathode-center HD-tDCS up to 2 mA, with a causal relationship in the information flow (equilibrium force transfer) from right to left that decreased over time. Conclusions: HD-tDCS intervention induced a dynamic influence over time on postural control entropy. Right hemisphere TPJ stimulation using cathode-center HD-tDCS can induce an asymmetry of body weight distribution towards the ipsilateral side of stimulation. These results support the clinical potential of HD-tDCS for post-stroke rehabilitation

Comparisons between time-points of SVV assessment for the tDCS conditions.

<p>Comparisons between time-points of SVV assessment for the tDCS conditions.</p

Descriptive data of SVV for each time and condition, and comparisons between pairs of conditions for time-points of SVV assessment.

<p>Descriptive data of SVV for each time and condition, and comparisons between pairs of conditions for time-points of SVV assessment.</p

Sensitivity analysis of vertical perception tDCS using Finite Element Analysis.

<p>Bilateral temporal-parietal region stimulation with 5cm diameter electrodes was modeled in “two subjects,” each using two different conductivity sets, “Standard” and “H1”. Electric field (V/m) and current density (A/m²) were predicted for 2mA of stimulation. Columns 1 and 2 demonstrate the relative electrode position with current streamlines, whose radii are proportional to the logarithm of current density. The magenta ring represents the location of the axial slice in the far right column. Simulations using standard conductivity values resulted in diffuse electric field throughout the parietal lobe, while H1 conductivity values resulted in more concentrated cortical stimulation. Across two head models and two conductivity sets, the most reliable cortical and subcortical regions of influence were under the electrodes.</p

“Bucket method” for measuring Subjective Visual Vertical.

<p>Note the exterior digital inclinometer (left) and interior line reference.</p

Mean and standard error of SVV scores for tDCS conditions at different times.

<p>Before tDCS (T0 = Baseline), during tDCS (T1 = 0.5min: 30 seconds after the start of stimulation; T2 = 15min: 15 minutes after the beginning of stimulation); and after tDCS (T3 = 20min: immediately after; T4 = 35min: 15 minutes after the end of stimulation; T5 = 50min: 30 minutes after the stimulation).</p

How do extrinsic factors influence the decision of young adults to become an entrepreneur?

‘How do extrinsic factors influence the decision of young adults to become an entrepreneur?’ Michelle Hartmann and Aiko Thumm, 2018: Applied Double Degree Bachelor, Linnaeus University Växjö, Sweden and ICN Business School Nancy, France. Even though governments all over the world are putting a spotlight on entrepreneurs and entrepreneurship as a whole, the motivations of why to become a venture creator is rarely touched upon. In general, there are two forms of possible influences on entrepreneurial intentions, namely intrinsic and extrinsic drivers. In order to further describe the phenomenon of extrinsic factors influencing entrepreneurial intentions, this study aims to describe the interplay of three extrinsic factors for venture creation. These three factors are entrepreneurship enhancing education, role models as well as influence of opportunity and necessity. A descriptive, qualitative study has been chosen for that purpose. During semi-structured interviews, the narrative story of the six participants is told. The findings revolve around the narratives of the respondents’ propositions towards the three aforementioned extrinsic factors. This paper shows that the present educational system only partially conveys necessary knowledge and entrepreneurial skills. Furthermore, this study suggests, that there is more than only a positively influencing role model, videlicet, a negative example representing things the young adult does not want to become. In addition, the study depicts the predicament of a clear differentiation between necessity and opportunity entrepreneurship. Lastly this paper concludes, that more than one factor are motivational drivers for young entrepreneurs and therefore opens a wide research area for future fellow entrepreneurship researchers