The Correlation between EEG Signals as Measured in Different Positions on Scalp Varying with Distance

© 2018 The Author(s). Published by Elsevier B. V. This is an open access article under the CC BY-NC-ND license https://creativecommons.org/licenses/by-nc-nd/4.0/Biomedical signals such as electroencephalogram (EEG) are the time varying signal, and different position of electrodes give different time varying signals. There might be a correlation between these signals. It is likely that the correlation is related to the actual position of electrodes. In this paper, we show that correlation is related to the physical distance between electrodes as measured. This finding is independent of participants and brain hemisphere. Our results indicate that the EEG signal is not transmitted via neurons but through white matter in a brain.Peer reviewedFinal Published versio

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 299)

This bibliography lists 96 reports, articles, and other documents introduced into the NASA scientific and technical information system in June, 1987

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 129, June 1974

This special bibliography lists 280 reports, articles, and other documents introduced into the NASA scientific and technical information system in May 1974

Effects of hypergravity on manual forces and displacements: causes and practical implications

ZUSAMMENFASSUNG Zahlreiche Studien haben die menschliche Motorik in Phasen erhöhter Erdbeschleunigung (+Gz) untersucht und Defizite z.B. bei Folge-, Zeige- und Kraftproduktionsaufgaben gefunden. Im letzteren Fall führte +Gz zu stark überhöhten Armkräften, wenn die Probanden einen isometrischen Joystick verwendeten. Da viele Hochleistungsflugzeuge durch solche Joysticks kontrolliert werden, könnten diese überhöhten Kräfte die Flugstabilität beeinträchtigen und daher die Sicherheit der Piloten während +Gz Flugmanövern wie Loopings und Kurven gefährden. Jedoch bleiben zahlreiche Fragen in diesem Kontext unklar: Reduziert sich die Krafterhöhung in +Gz durch ein Training? Zeigt sich bei +Gz-erfahrenen Piloten die gleiche Krafterhöhung wie bei +Gz-unerfahrenen Probanden? Sind manuelle Auslenkungen mit einem regulären Joystick wie er in anderen Flugzeugmodellen genutzt wird ebenfalls durch +Gz beeinträchtigt? Hat +Gz auch einen Einfluss auf Prozesse des motorischen Lernens? Solche Fragen beziehen sich alle auf den operativen Hintergrund von Piloten, die Hochleistungsjets fliegen, und entsprechende Antworten könnten helfen, die Flugausbildung und den Arbeitsalltag solcher Piloten zu verbessern. Neben diesen anwendungsorientierten Fragen ist eine andere, grundlegende Frage auffallend: Warum produzieren Probanden erhöhte isometrische Kräfte in +Gz? Entsprechend der Literatur sind einige potentielle Gründe wie mechanische Aspekte, gestörtes Sehvermögen oder propriozeptive Defizite nicht in der Lage diesen Effekt zu erklären, wohingegen andere Aspekte, wie kognitive Belastung, körperliche Aktivität, vestibulo-spinale Aktivität oder psycho-physiologischer Stress tatsächlich die beobachtete Krafterhöhung in +Gz erklären könnten. Allerdings fehlen nützliche wissenschaftliche Daten, die diese letzten Theorien unterstützen würden. Daher beinhaltet diese Promotion die Untersuchung sowohl von Fragen zur Motorik in Bezug auf fliegerische Tätigkeiten, als auch von möglichen Gründen für die +Gz-bedingte Krafterhöhung, um so das aktuelle Wissen in anwendungs- und grundlagenorientierten wissenschaftlichen Themen zur Motorik in +Gz zu erweitern. Hinsichtlich der wissenschaftlichen Fragestellungen bezogen auf fliegerische Tätigkeiten konnten wir zeigen, dass die beobachtete Erhöhung isometrischer Kräfte in +Gz partiell durch ein anhaltendes Training in +Gz ausgeglichen werden konnte, wohingegen ein gleichwertiges Training bei normaler Erdbeschleunigung entsprechend eines Simulatortrainings auf der Erde unwirksam war. Darüber hinaus konnte eine längerfristige Gewöhnung an die +Gz Umgebung nicht beobachtet werden, da professionelle Jetpiloten, die in Trainingsflügen regelmäßig +Gz ausgesetzt sind, nur eine geringfügig kleinere Verschlechterung bei der isometrischen Kraftproduktion zeigen als +Gz-unerfahrene Probanden. Ferner konnten wir zeigen, dass weder manuelle Auslenkungen eines regulären Joysticks, noch die Fähigkeit der Probanden, ihre Motorik an unbekannte Situationen anzupassen, negativ durch +Gz beeinträchtigt sind. Die Untersuchung möglicher Gründe für die beobachtete Krafterhöhung in +Gz zeigte, dass auch eine kognitive Belastung als zugrundeliegender Mechanismus für den Kraftanstieg in +Gz unwahrscheinlich ist, da der kognitive Aufwand bei der Untersuchung mittels der Doppeltätigkeitsmethode nicht mit dem +Gz-Level variierte. Darüber hinaus konnten wir zeigen, dass körperliche Aktivität die isometrische Kraftproduktion beeinträchtigt, sich dieser Effekt aber qualitativ von der beobachteten Krafterhöhung in +Gz unterscheidet, so dass körperliche Aktivität wahrscheinlich ebenfalls nicht der Grund für die erhöhte Kraftproduktion in +Gz ist. Im Gegensatz dazu beschreibt die vorliegende Promotion Experimente zur Kraftproduktion während Phasen von linearer Vektion, welche die Vermutung unterstützen, dass eine gesteigerte vestibulo-spinale Aktivität ein Grund für die erhöhte Kraftproduktion in +Gz ist. Zusätzlich könnten auch +Gz bedingte psycho-physiologische Veränderungen ein relevanter Faktor sein, da wir zeigen konnten, dass +Gz zu einem umfassenden Anstieg in unterschiedlichen Stresshormonkonzentrationen führt, welche einhergeht mit einer Reduktion der wahrgenommenen körperlichen und mentalen Verfassung. Da manuelle Auslenkungen weder in +Gz, bei vestibulärer Stimulation noch bei körperlicher Aktivität beeinträchtigt waren, scheinen die zugrundeliegenden Mechanismen nur Kräfte, jedoch keine Bewegungen zu beeinflussen. SUMMARY Several scientific studies have examined human motor performance during phases of increased terrestrial gravitational acceleration (+Gz), and found deficits e.g. in tracking, pointing and force production tasks. In the latter case, +Gz provoked highly exaggerated arm forces when subjects used an isometric joystick. Since several high-performance aircraft are controlled by such sticks this force exaggeration might impair flight stability and could therefore compromise pilots’ safety during +Gz flight maneuvers as loops and turns. However, several questions in this context remain unclear: Is the observed force exaggeration in +Gz reduced by training? Do +Gz-experienced fighter pilots show the same force exaggeration like +Gz-inexperienced subjects? Are manual displacements with a regular joystick used in different aircraft affected by +Gz as well? Does +Gz have an impact on motor learning processes? Such questions all relate to the operational background of pilots flying high-performance aircraft and answers might help to improve pilots’ flight trainings and their working lives. Besides these applied questions, another fundamental question is striking: Why do subjects produce exaggerated isometric forces in +Gz? According to literature some possible reasons like mechanical aspects, disturbed vision or proprioceptive deficits cannot explain this effect, while other aspects, like computational stress, physical activation, vestibulo-spinal activity or psycho-physiological stress might indeed explain the observed force exaggeration in +Gz. However, valuable scientific data supporting these latter theories are missing. Therefore, in order to enhance the current knowledge of applied as well as basic research topics on motor performance in +Gz, this thesis contains the investigation of both questions on motor performance related to flight operations as well as possible causes of the +Gz-induced force exaggeration. Pertaining to the research questions on motor performance related to flight operations we could show that the observed isometric force exaggeration in +Gz can be partly compensated by a prolonged task practice in +Gz, while an equivalent practice conducted in normal gravitational acceleration adequate to simulation training on the ground was ineffective. Furthermore, long term adaptation to the +Gz environment could not be observed, since professional jet pilots frequently exposed to +Gz during practice flights only showed a slightly smaller deficit in isometric force production than +Gz-inexperienced subjects. We could further demonstrate, that neither manual displacements with a regular joystick nor subjects’ ability to adapt their motor performance to unknown situations are affected negatively by +Gz. The investigation of possible causes of the observed force exaggeration in +Gz showed that also computational stress seems unlikely as an underlying reason for the force increase in +Gz, since the cognitive demand investigated by the dual task approach did not vary with the +Gz-level. We could further show that physical exercise impairs isometric force production, but since this effect differed qualitatively to the observed force exaggeration in +Gz, physical activation does probably not explain this force exaggeration in +Gz, either. In contrast, the present thesis describes experiments on force production during phases of linear vection supporting the assumption that increased vestibulo-spinal activity might be a cause of the observed force exaggeration in +Gz. Additionally, +Gz-related psycho-physiological changes might also be a relevant factor, as we could demonstrate that +Gz induces a comprehensive increase in various stress hormone concentrations going along with a decrease in perceived physical and mental state. Since manual displacements were neither affected by +Gz, vestibular stimulation nor physical activity, these underlying mechanisms seem to affect only forces, but do not apply for displacements

Vibration

Physiological and biomechanical responses of humans to vibrations during manned space flight and threshold data on tolerances to various vibrational modes and condition

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 125

This special bibliography lists 323 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1974

Adaptation to prolonged bedrest in man: A compendium of research

A compilation of major studies that describe the clinical observations and elucidate the physiological mechanisms of the adaptive process of man undergoing prolonged bed rest is presented. Additional studies are included that provide background information in the form of reviews or summaries of the process. Wherever possible a detailed annotation is provided under the subheadings: (1) purpose, (2) procedure and methods, (3) results, and (4) conclusions. Additional references are provided in a selected bibliography

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 130, July 1974

This special bibliography lists 291 reports, articles, and other documents introduced into the NASA scientific and technical information system in June 1974

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 164

This bibliography lists 275 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1977

Assessing Variability of EEG and ECG/HRV Time Series Signals Using a Variety of Non-Linear Methods

Time series signals, such as Electroencephalogram (EEG) and Electrocardiogram (ECG) represent the complex dynamic behaviours of biological systems. The analysis of these signals using variety of nonlinear methods is essential for understanding variability within EEG and ECG, which potentially could help unveiling hidden patterns related to underlying physiological mechanisms. EEG is a time varying signal, and electrodes for recording EEG at different positions on the scalp give different time varying signals. There might be correlation between these signals. It is important to know the correlation between EEG signals because it might tell whether or not brain activities from different areas are related. EEG and ECG might be related to each other because both of them are generated from one co-ordinately working body. Investigating this relationship is of interest because it may reveal information about the correlation between EEG and ECG signals. This thesis is about assessing variability of time series data, EEG and ECG, using variety of nonlinear measures. Although other research has looked into the correlation between EEGs using a limited number of electrodes and a limited number of combinations of electrode pairs, no research has investigated the correlation between EEG signals and distance between electrodes. Furthermore, no one has compared the correlation performance for participants with and without medical conditions. In my research, I have filled up these gaps by using a full range of electrodes and all possible combinations of electrode pairs analysed in Time Domain (TD). Cross-Correlation method is calculated on the processed EEG signals for different number unique electrode pairs from each datasets. In order to obtain the distance in centimetres (cm) between electrodes, a measuring tape was used. For most of our participants the head circumference range was 54-58cm, for which a medium-sized I have discovered that the correlation between EEG signals measured through electrodes is linearly dependent on the physical distance (straight-line) distance between them for datasets without medical condition, but not for datasets with medical conditions. Some research has investigated correlation between EEG and Heart Rate Variability (HRV) within limited brain areas and demonstrated the existence of correlation between EEG and HRV. But no research has indicated whether or not the correlation changes with brain area. Although Wavelet Transformations (WT) have been performed on time series data including EEG and HRV signals to extract certain features respectively by other research, so far correlation between WT signals of EEG and HRV has not been analysed. My research covers these gaps by conducting a thorough investigation of all electrodes on the human scalp in Frequency Domain (FD) as well as TD. For the reason of different sample rates of EEG and HRV, two different approaches (named as Method 1 and Method 2) are utilised to segment EEG signals and to calculate Pearson’s Correlation Coefficient for each of the EEG frequencies with each of the HRV frequencies in FD. I have demonstrated that EEG at the front area of the brain has a stronger correlation with HRV than that at the other area in a frequency domain. These findings are independent of both participants and brain hemispheres. Sample Entropy (SE) is used to predict complexity of time series data. Recent research has proposed new calculation methods for SE, aiming to improve the accuracy. To my knowledge, no one has attempted to reduce the computational time of SE calculation. I have developed a new calculation method for time series complexity which could improve computational time significantly in the context of calculating a correlation between EEG and HRV. The results have a parsimonious outcome of SE calculation by exploiting a new method of SE implementation. In addition, it is found that the electrical activity in the frontal lobe of the brain appears to be correlated with the HRV in a time domain. Time series analysis method has been utilised to study complex systems that appear ubiquitous in nature, but limited to certain dynamic systems (e.g. analysing variables affecting stock values). In this thesis, I have also investigated the nature of the dynamic system of HRV. I have disclosed that Embedding Dimension could unveil two variables that determined HRV