False positives associated with responder/non-responder analyses based on motor evoked potentials

Background: A trend in the non-invasive brain stimulation literature is to assess the outcome of an intervention using a responder analysis whereby participants are di- or trichotomised in order that they may be classified as either responders or non-responders. Objective: Examine the extent of the Type I error in motor evoked potential (MEP) data subjected to responder analyses. Methods: Seven sets of 30 MEPs were recorded from the first dorsal interosseous muscle in 52 healthy volunteers. Four classification techniques were used to classify the participants as responders or non-responders: (1) the two-step cluster analysis, (2) dichotomised thresholding, (3) relative method and (4) baseline variance method. Results: Despite the lack of any intervention, a significant number of participants were classified as responders (21–71%). Conclusion: This study highlights the very large Type I error associated with dichotomising continuous variables such as the TMS MEP

Rapid assessment of corticospinal excitability using transcranial magnetic stimulation

Human motor system plasticity can be quantified using single pulse transcranial magnetic stimulation (TMS) to measure corticospinal excitability. TMS can be used to produce excitability maps and to examine the stimulus-response (SR) relationship. The overall aims of this thesis are (1) to demonstrate that TMS mapping and SR curves can be acquired much faster than has been traditionally possible and (2) that these techniques can be used to study internally externally driven plasticity. By modifying the TMS delivery, it is demonstrated that both the TMS map and the SR curve can be reliably produced in approximately two minutes. These techniques were then used to examine internally driven plasticity via mirror training and visuomotor tracking learning and externally driven plasticity via transcranial alternating current stimulation. Changes in corticospinal excitability were found to be variable both for internally as externally driven plasticity. Nonetheless, these studies highlight that it is possible to rapidly assess changes in corticospinal excitability

Interindividual Variability in Use-Dependent Plasticity Following Visuomotor Learning: The Effect of Handedness and Muscle Trained

Motor learning has been linked with increases in corticospinal excitability (CSE). However, the robustness of this link is unclear. In this study, changes in CSE associated with learning a visuomotor tracking task were mapped using transcranial magnetic stimulation (TMS). TMS maps were obtained before and after training with the first dorsal interosseous (FDI) of the dominant and nondominant hand, and for a distal (FDI) and proximal (biceps brachii) muscle. Tracking performance improved following 20 min of visuomotor training, while map area was unaffected. Large individual differences were observed with 18%–36% of the participants revealing an increase in TMS map area. This result highlights the complex relationship between motor learning and use-dependent plasticity of the motor cortex

Intra and inter-session reliability of rapid Transcranial Magnetic Stimulation stimulus-response curves of tibialis anterior muscle in healthy older adults

Objective: The clinical use of Transcranial Magnetic Stimulation (TMS) as a technique to assess corticospinal excitability is limited by the time for data acquisition and the measurement variability. This study aimed at evaluating the reliability of Stimulus-Response (SR) curves acquired with a recently proposed rapid protocol on tibialis anterior muscle of healthy older adults. Methods: Twenty-four neurologically-intact adults (age:55–75 years) were recruited for this test-retest study. During each session, six SR curves, 3 at rest and 3 during isometric muscle contractions at 5% of maximum voluntary contraction (MVC), were acquired. Motor Evoked Potentials (MEPs) were normalized to the maximum peripherally evoked response; the coil position and orientation were monitored with an optical tracking system. Intra- and inter-session reliability of motor threshold (MT), area under the curve (AURC), MEPmax, stimulation intensity at which the MEP is mid-way between MEPmax and MEPmin (I50), slope in I50, MEP latency, and silent period (SP) were assessed in terms of Standard Error of Measurement (SEM), relative SEM, Minimum Detectable Change (MDC), and Intraclass Correlation Coefficient (ICC). Results: The relative SEM was ≤10% for MT, I50, latency and SP both at rest and 5%MVC, while it ranged between 11% and 37% for AURC, MEPmax, and slope. MDC values were overall quite large; e.g., MT required a change of 12%MSO at rest and 10%MSO at 5%MVC to be considered a real change. Inter-sessions ICC were >0.6 for all measures but slope at rest and MEPmax and latency at 5%MVC. Conclusions: Measures derived from SR curves acquired in <4 minutes are affected by similar measurement errors to those found with long-lasting protocols, suggesting that the rapid method is at least as reliable as the traditional methods. As specifically designed to include older adults, this study provides normative data for future studies involving older neurological patients (e.g. stroke survivors)

StimTrack: An open-source software for manual transcranial magnetic stimulation coil positioning

Background: During Transcranial Magnetic Stimulation (TMS) experiments researchers often use a neuronavigation system to precisely and accurately maintain coil position and orientation. New method: This study aimed to develop and validate an open-source software for TMS coil navigation. StimTrack uses an optical tracker and an intuitive user interface to facilitate the maintenance of position and orientation of any type of coil within and between sessions. Additionally, online access to navigation data is provided, hereby adding e.g. the ability to start or stop the magnetic stimulator depending on the distance to target or the variation of the orientation angles. Results: StimTrack allows repeatable repositioning of the coil within 0.7 mm for translation and 0.9) was obtained on all parameters computed on SR curves acquired using StimTrack. Comparison with existing method: StimTrack showed a target accuracy similar to that of a commercial neuronavigation system (BrainSight, Rogue Research Inc.). Indeed, small differences both in position (∼0.2 mm) and orientation (<1°) were found between the systems. These differences are negligible given the human error involved in landmarks registration. Conclusions: StimTrack, available as supplementary material, is found to be a good alternative for commercial neuronavigation systems facilitating assessment changes in corticospinal excitability using TMS. StimTrack allows researchers to tailor its functionality to their specific needs, providing added value that benefits experimental procedures and improves data quality

The TMS Map Scales with Increased Stimulation Intensity and Muscle Activation

One way to study cortical organisation, or its reorganisation, is to use transcranial magnetic stimulation (TMS) to construct a map of corticospinal excitability. TMS maps are reported to be acquired with a wide variety of stimulation intensities and levels of muscle activation. Whilst MEPs are known to increase both with stimulation intensity and muscle activation, it remains to be established what the effect of these factors is on the map's centre of gravity (COG), area, volume and shape. Therefore, the objective of this study was to systematically examine the effect of stimulation intensity and muscle activation on these four key map outcome measures. In a first experiment, maps were acquired with a stimulation intensity of 110, 120 and 130% of resting threshold. In a second experiment, maps were acquired at rest and at 5, 10, 20 and 40% of maximum voluntary contraction. Map area and map volume increased with both stimulation intensity (P 0.09 in all cases). This result indicates the map simply scales with stimulation intensity and muscle activation

Pre-Estimated Spectral Rendering

Spectral Monte Carlo renderers are capable of reproducing several advanced phenomena of light, such as chromatic dispersion and fluorescence. As spectral renderers must sample the spectral domain, they are typically hampered by a multitude of sampling issues leading to notably poor convergence rates, which are reinforced when realistic emission or reflectance spectra are involved in otherwise simple scenes. We propose pre-estimated spectral rendering, which is a simple method that iteratively builds estimates of spectral radiance distributions before rendering, and subsequently uses these to efficiently guide importance sampling of the spectral domain. Our method significantly lowers variance and reduces chromatic noise with little overhead in multiple difficult scenarios, which we demonstrate with an implementation in a conventional renderer

TMS assessed cortical representation scales with stimulation intensity and muscle activation

Transcranial magnetic stimulation (TMS) is routinely used to construct a map of corticospinal excitability (CSE). TMS elicited motor evoked potentials (MEPs) are known to increase both with stimulation intensity and muscle activation. Whilst a wide variety of stimulation intensities and levels of muscle activation are used to generate TMS maps, their effect on the cortical representation has yet to be systematically explored. Two experiments were performed to describe the effect of stimulation intensities (Experiment 1) and muscle activation (Experiment 2) on the map outcome measures: aspect ratio, centre of gravity (COG), map area and map volume. Twelve participants were recruited for each experiment. TMS maps were acquired from the first dorsal interosseous (FDI). Maps were acquired using 80 stimuli pseudorandomly across a 6x6 cm area with a 1.5 s interstimulus interval, allowing the maps to be acquired in two minutes. In Experiment 1 maps were compared at 5, 10, 20 and 40% of the maximum voluntary contraction. All maps were acquired with a stimulation intensity of 120% of the resting motor threshold (RMT). In Experiment 2 maps were compared at the stimulation intensities of 110, 120 and 130% of RMT, whilst the muscle was at rest. A significant increase in map area and map volume were observed with stimulation intensity and level of muscle activation as would be expected. Neither the COG nor the aspect ratio were changed with either increased stimulation intensity or muscle activation. This study demonstrates that the cortical representation scales with stimulation intensity and level of muscle activation, but the shape of the map does not change

Novel tools for rapid online data acquisition of the TMS stimulus-response curve

Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Biomechatronics & Human-Machine Contro

Improving the Plugify Admin Panel

In this report, we present our work on improving the administration software and automating parts of the customer service work for Plugify (https://www.plugify.nl), a young Dutch startup that provides an online music act booking platform. We first analyze Plugify's needs, and then discuss how we design, develop, and iterate the systems they require. We leverage and customize pre-existing administration software named ForestAdmin to provide us with a stable administration panel to create and modify data. Furthermore, we rework Plugify's existing internal notification system to be smarter. Then, we create a small number of custom web pages for Plugify's customer service to more easily process relevant data. Finally, we provide Plugify with a system for metrics in an intelligent way. We also discuss how we perform unit, integration and usability testing, to ensure, among others, the stability, reliability, usability, performance and completeness of the systems we have built.Computer Scienc