Browsing by Author "Comaduran Marquez, Daniel"
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- ItemOpen AccessDesign and Development of a Multichannel Current-EMG System for Coherence Analysis(2016) Comaduran Marquez, Daniel; Nigg, Benno; Murari, Kartikeya; Von Tscharner, Vinzenz; Herzog, WalterElectromyography (EMG), the methodology to record muscle activity, has been unchanged for many years, with the use of instrumentation amplifiers (IAs). To overcome limitations of IAs when measuring EMG activity from pennate muscles, a transimpedance amplifier (TIA) has been proposed [1]. The TIA has the advantage of conserving all frequency information in the EMG signal. However, there are some limitations of the originally proposed current-amplifier. In this thesis, we present the design and development of an improved current-amplifier. Additionally, an isolation module was developed to record from multiple muscles simultaneously. The new current-amplifier was used in two experiments. The first experiment was conducted to test coherence, a metric that determines similarity in the frequency content of two signals, as an indicator of fatigue during a dynamic activity. The second experiment was conducted to test the ability of a biofeedback system to modulate coherence.
- ItemOpen AccessDevelopment and Validation of a Current-Based EEG System for Tangential Current Measurement(2021-09-10) Comaduran Marquez, Daniel; Murari, Kartikeya; Sotero-Diaz, Roberto C.; Federico, PaoloVoltage-based electroencephalography (vEEG) and magnetoencephalography (MEG) are among the state-of-the-art non-invasive methodologies to study the electrophysiology of the human brain. Both methodologies offer high temporal but limited spatial resolution. vEEG and MEG are sensitive to radially and tangentially oriented dipoles in the brain, respectively. This complementary information improves the achievable spatial resolution when used simultaneously in source localization applications (e.g., locating epilepsy foci). However, MEG is not as easily accessible as vEEG. The initial setup cost of an MEG system is in the order of millions of US dollars (USD), and the yearly operational cost can be hundreds of thousands of USD. Conversely, a high-end vEEG system can be acquired for tens of thousands of USD and require minimal maintenance. In some topologies, vEEG can measure from tangential dipoles, but suffers from fundamental limitations regarding signal strength. To address the technological need for a more accessible technology than MEG that can measure tangential dipoles in the brain, I developed a current-based EEG (cEEG) system. The cEEG has a front-end transimpedance amplifier to measure currents that are caused by tangential dipoles. A one-channel cEEG amplifier was conceptualized, designed, simulated, implemented, and characterized for validating the proposed current-based technology. The characterization met design goals set to reliably measure brain currents. Using phantom and simulation models, I found that cEEG is mostly influenced by tangential dipoles. Further, the cEEG was used to measure alpha waves during a resting, and steady-state visual evoked potentials paradigms to measure brain activity from ten healthy individuals. Statistical analysis of the experimental data showed that the cEEG could effectively measure brain activity. Towards the development of a multichannel system, a second cEEG was developed with a microcontroller for on-board digitization of the amplified and filtered signal. This implementation allows the cEEG to have isolated power supplies, which are required if multiple amplifiers were to be used. cEEG systems open up the possibility to understand brain activity from a different perspective in research and clinical applications.
- ItemOpen AccessFatigue in children using motor imagery and P300 brain-computer interfaces(2024-04-24) Keough, Joanna R.; Irvine, Brian; Kelly, Dion; Wrightson, James; Comaduran Marquez, Daniel; Kinney-Lang, Eli; Kirton, AdamAbstract Background Brain-computer interface (BCI) technology offers children with quadriplegic cerebral palsy unique opportunities for communication, environmental exploration, learning, and game play. Research in adults demonstrates a negative impact of fatigue on BCI enjoyment, while effects on BCI performance are variable. To date, there have been no pediatric studies of BCI fatigue. The purpose of this study was to assess the effects of two different BCI paradigms, motor imagery and visual P300, on the development of self-reported fatigue and an electroencephalography (EEG) biomarker of fatigue in typically developing children. Methods Thirty-seven typically-developing school-aged children were recruited to a prospective, crossover study. Participants attended three sessions: (A) motor imagery-BCI, (B) visual P300-BCI, and (C) video viewing (control). The motor imagery task involved an imagined left- or right-hand squeeze. The P300 task involved attending to one square on a 3 × 3 grid during a random single flash sequence. Each paradigm had respective calibration periods and a similar visual counting game. Primary outcomes were self-reported fatigue and the power of the EEG alpha band both collected during resting-state periods pre- and post-task. Self-reported fatigue was measured using a 10-point visual analog scale. EEG alpha band power was calculated as the integrated power spectral density from 8 to 12 Hz of the EEG spectrum. Results Thirty-two children completed the protocol (age range 7–16, 63% female). Self-reported fatigue and EEG alpha band power increased across all sessions (F(1,155) = 33.9, p < 0.001; F = 5.0(1,149), p = 0.027 respectively). No differences in fatigue development were observed between session types. There was no correlation between self-reported fatigue and EEG alpha band power change. BCI performance varied between participants and paradigms as expected but was not associated with self-reported fatigue or EEG alpha band power. Conclusion Short periods (30-mintues) of BCI use can increase self-reported fatigue and EEG alpha band power to a similar degree in children performing motor imagery and P300 BCI paradigms. Performance was not associated with our measures of fatigue; the impact of fatigue on useability and enjoyment is unclear. Our results reflect the variability of fatigue and the BCI experience more broadly in children and warrant further investigation.