The Effects of Filter's Class, Cutoff Frequencies, and Independent Component Analysis on the Amplitude of Somatosensory Evoked Potentials Recorded from Healthy Volunteers

Objective: The aim of this study was to investigate the effects of different preprocessing parameters on the amplitude of median nerve somatosensory evoked potentials (SEPs). Methods: Different combinations of two classes of filters (Finite Impulse Response (FIR) and Infinite Impulse Response (IIR)), three cutoff frequency bands (0.5–1000 Hz, 3–1000 Hz, and 30–1000 Hz), and independent component analysis (ICA) were used to preprocess SEPs recorded from 17 healthy volunteers who participated in two sessions of 1000 stimulations of the right median nerve. N30 amplitude was calculated from frontally placed electrode (F3). Results: The epochs classified as artifacts from SEPs filtered with FIR compared to those filtered with IIR were 1% more using automatic and 140% more using semi-automatic methods (both p < 0.001). There were no differences in N30 amplitudes between FIR and IIR filtered SEPs. The N30 amplitude was significantly lower for SEPs filtered with 30–1000 Hz compared to the bandpass frequencies 0.5–1000 Hz and 3–1000 Hz. The N30 amplitude was significantly reduced when SEPs were cleaned with ICA compared to the SEPs from which non-brain components were not removed using ICA. Conclusion: This study suggests that the preprocessing of SEPs should be done carefully and the neuroscience community should come to a consensus regarding SEP preprocessing guidelines, as the preprocessing parameters can affect the outcomes that may influence the interpretations of results, replicability, and comparison of different studies

Motor imagery-based brain-computer interface by implementing a frequency band selection

Les interfícies cervell-ordinador basades en imaginacions motores (MI-BCI) són una promesa per a revolucionar la manera com els humans interactuen amb les màquines o el programari, realitzant accions només amb el pensament. Els pacients que pateixen discapacitats de moviment crítiques, com l'esclerosi lateral amiotròfica (ALS) o la tetraplegia, podrien utilitzar aquesta tecnologia per controlar una cadira de rodes, pròtesis robòtiques o qualsevol altre dispositiu que els permeti interactuar de manera independent amb el seu entorn. L'objectiu d'aquest projecte és ajudar les comunitats afectades per aquests trastorns amb el desenvolupament d'un mètode que sigui capaç de detectar, amb la màxima precisió possible, la intenció d'executar moviments (sense que es produeixin) en les extremitats superiors del cos. Això es farà mitjançant senyals adquirits amb un electroencefalograma (EEG), el seu condicionament i processament, i la seva posterior classificació amb models d'intel·ligència artificial. A més, es dissenyarà un filtre de senyal digital per mantenir les bandes de freqüència més característiques de cada individu i augmentar significativament l’exactitud del sistema. Després d'extreure les característiques estadístiques, freqüencials i espacials més discriminatòries, va ser possible obtenir una exactitud del 88% en les dades de validació a l'hora de detectar si un participant estava imaginant un moviment de la mà esquerra o de la dreta. A més, es va utilitzar una xarxa neuronal convolucional (CNN) per distingir si el participant estava imaginant un moviment o no, la qual cosa va aconseguir una exactitud del 78% i una precisió del 90%. Aquests resultats es verificaran mitjançant la implementació d'una simulació en temps real amb l'ús d'un braç robòtic.Las interfaces cerebro-computadora basadas en imaginaciones motoras (MI-BCI) son una promesa para revolucionar la forma en que los humanos interactúan con las máquinas o el software, realizando acciones con tan solo pensar en ellas. Los pacientes que sufren discapacidades críticas del movimiento, como la esclerosis lateral amiotrófica (ALS) o la tetraplejia, podrían usar esta tecnología para controlar una silla de ruedas, prótesis robóticas o cualquier otro dispositivo que les permita interactuar de manera independiente con su entorno. El objetivo de este proyecto es ayudar a las comunidades afectadas por estos trastornos con el desarrollo de un método que sea capaz de detectar, con la mayor precisión posible, la intención de ejecutar movimientos (sin que se produzcan) en las extremidades superiores del cuerpo. Esto se hará mediante señales adquiridas con un electroencefalograma (EEG), su acondicionamiento y procesamiento, y su posterior clasificación con modelos de inteligencia artificial. Además, se diseñará un filtro de señal digital para mantener las bandas de frecuencia más características de cada individuo y aumentar significativamente la exactitud del sistema. Después de extraer características estadísticas, frecuenciales y espaciales discriminatorias, fue posible obtener una exactitud del 88% en los datos de validación a la hora de detectar si un participante estaba imaginando un movimiento con la mano izquierda o con la derecha. Además, se utilizó una red neural convolucional (CNN) para distinguir si el participante estaba imaginando un movimiento o no, lo que logró un 78% de exactitud y un 90% de precisión. Estos resultados se verificarán implementando una simulación en tiempo real con el uso de un brazo robótico.Motor Imagery-based Brain-Computer Interfaces (MI-BCI) are a promise to revolutionize the way humans interact with machinery or software, performing actions by just thinking about them. Patients suffering from critical movement disabilities, such as amyotrophic lateral sclerosis (ALS) or tetraplegia, could use this technology to control a wheelchair, robotic prostheses, or any other device that could let them interact independently with their surroundings. The focus of this project is to aid communities affected by these disorders with the development of a method that is capable of detecting, as accurately as possible, the intention to execute movements (without them occurring) in the upper extremities of the body. This will be done through signals acquired with an electroencephalogram (EEG), their conditioning and processing, and their subsequent classification with artificial intelligence models. In addition, a digital signal filter will be designed to keep the most characteristic frequency bands of each individual and increase accuracy significantly. After extracting discriminative statistical, frequential, and spatial features, it was possible to obtain an 88% accuracy on validation data when it came to detecting whether a participant was imagining a left-hand or a right-hand movement. Furthermore, a Convolutional Neural Network (CNN) was used to distinguish if the participant was imagining a movement or not, which achieved a 78% accuracy and a 90% precision. These results will be verified by implementing a real-time simulation with the usage of a robotic arm

Diabetes mellitus type 2; The incretin effect and interaction with the autonomic nervous system

Bakgrunn: Inkretineffekten er kroppens evne til økt insulinsekresjon når glukose inntas peroralt sammenliknet med administrert intravenøst, utløst av spesifikke hormoner fra tarmen. En redusert inkretineffekt leder til forhøyet blodsukker etter måltid, og er et tidlig fenomen ved diabetes type 2, også påvist i forstadier til diabetes, såkalt prediabetes, og ved fedme. En bevart inkretineffekt ser delvis ut til å være avhengig av et intakt autonomt nervesystem. Autonom nevropati har vært betraktet som en sen komplikasjon til diabetes mellitus, men det er økende evidens for at nevropati også kan oppstå tidlig i forløpet. Kjennskap til disse faktorene ledet oss til en hypotese om at tidlig autonom nevropati kan bidra til den reduserte inkretineffekten ved diabetes type 2. Mål: Vårt primære mål var å undersøke om det var assosiasjon mellom inkretineffekt og grad av autonom nevropati. Sekundære mål var å se på inkretineffekten relatert til grad av hyperglykemi og varighet av diabetes, og sammenlikne en ny test som innebærer ballongdilatasjon i rektum, som mål for tarmens sensitivitet og videre signaloverføring, med mer etablerte tester for nevropati. Et siste sekundærmål var å undersøke gjennomførbarheten av en norsk versjon av spørreskjemaet, «Composite Autonomic Symptom Score» (COMPASS) 31, som kan påvise mulige symptomer fra autonom dysfunksjon, og vi testet om dette var assosiert med øvrige nerveundersøkelser. Metode: Tre grupper ble inkludert; en gruppe med diabetes type 2 varighet >10 år, en gruppe med nyoppdaget type 2 diabetes siste året, uten behov for medikamentell behandling, og en kontrollgruppe matchet for alder, kjønn og kroppsmasseindeks. Inkretineffekten ble kalkulert fra c-peptid (areal under kurven) ved oral glukosebelastning sammenliknet med intravenøs isoglykemisk glukose infusjon. Gastrointestinal glukose-håndtering (GIGD) ble kalkulert fra glukose gitt oralt sammenliknet med glukose tilført intravenøst. Tester for nevropati inkluderte kardiovaskulære reflekstester, hjertefrekvensvariabilitet, svettefunksjon, nerveledningshastighet i nervus suralis og monofilament test. Som mål på gastrointestinal visceral nervefunksjon utførte vi rektal ballongdilatasjon med registrering av trykk for første følelse av dilatasjon og ubehagelig følelse av dilatasjon. Evokerte hjernepotensial ble målt som respons på ballongdilatasjon ved gjentatte stimuli av nevnte trykk. Spørreskjemaet COMPASS 31 ble besvart digitalt. Resultat: Deltakerne med diabetes trengte høyere trykk for å oppnå første følelse av ballongdilatasjon i rektum, uavhengig av diabetesvarighet. Økt behov for trykk korrelerte med nedsatt GIGD, men ikke med inkretineffekt. Økt behov for trykk korrelerte også med nedsatt følelse på monofilament test. GIGD og inkretineffekt korrelerte signifikant med både grad av hyperglykemi og diabetesvarighet. Det ble funnet få tilfeller av nevropati totalt sett, og få forskjeller mellom gruppene. Det var en tendens til at lenger latenstid og mindre amplituder på evokerte hjernepotensial var assosiert med lavere hjertefrekvensvariabilitet og kardiovaskulære reflekstester, sural nerveledning og monofilament test, men ikke statistisk signifikant etter korreksjon for multippel testing. Høyere score på COMPASS 31 ble funnet hos dem med langvarig diabetes og hos kvinner, med best sensitivitet og negativ prediktiv verdi for score <10. Konklusjon: Vi fant rektal hyposensitivitet både ved langvarig og tidlig type 2 diabetes og dette var assosiert med redusert GIGD, men ikke med redusert inkretineffekt. Dette kan tyde på at adekvat nervefunksjon i tarmen er viktig for andre faktorer enn inkretineffekten i håndteringen av glukose. Redusert GIGD og inkretineffekt er assosiert med økende hyperglykemi og varighet av diabetes, som viser et kontinuum i tarmens glukosehåndtering fra normo- til hyperglykemi. Vi fant klinisk plausible tegn på at sentral nerveledning er assosiert med perifer nervefunksjon, men resultatene må tolkes med forsiktighet, gitt multippel testing. Rektal ballongdilatasjon med måling av sensitivitet og evokerte hjernepotensial synes å være en lovende metode for undersøkelse av nervefunksjon i tarmen, også når øvrige autonome tester er normale. Til sist finner vi spørreskjemaet COMPASS 31 lovende til bruk både i forskning, men også i den kliniske hverdag, hvor autonome symptomer ofte er neglisjert. I en liknende populasjon som vår vil en score på 10 poeng eller mindre nærmest utelukke kardiovaskulær autonom nevropati.Background: The incretin effect refers to the amplified insulin response when glucose is administered orally compared to intravenously. A reduced incretin effect is found at early stages of type 2 diabetes, even in prediabetes and obesity, but the mechanisms behind are unknown. Evidence suggests that part of the effect of incretin hormones are mediated through vagal nerve transmission. Diabetic autonomic neuropathy is considered a late complication of diabetes mellitus, but there is an increasing awareness that neuropathy can exist in both prediabetes and early stages of diabetes. This led us to the hypothesis that the incretin effect could be affected by early autonomic neuropathy because of a reduced transmission of signals. Aims: Our main objective was to explore whether a reduced incretin effect could be associated with autonomic neuropathy. Secondarily, we aimed to explore the incretin effect in relation to degree of dysglycemia and the duration of diabetes. Other secondary objectives were to explore a novel test of gut visceral sensitivity and central transmission of peripheral signals, and to compare it with established tests for diabetic neuropathy, including assessment of symptoms using the Composite Autonomic Symptom Score (COMPASS) 31. Methods: This was case-control study including three groups of participants: People with type 2 diabetes for >10 years (longstanding), people with newly discovered type 2 diabetes within the last year, without the need for antidiabetic medication (early), and a group of matched controls in age, sex, and body mass index. An oral glucose tolerance test followed by an intravenous isoglycemic glucose infusion were performed to calculate the incretin effect (from c-peptide area under the curve). Gastrointestinal-mediated glucose disposal (GIGD) was calculated as an estimate of the body’s ability to cope with the challenge of a carbohydrate ingestion. Neuropathy tests included cardiovascular reflex tests, heart rate variability, sudomotor function, sural nerve, and the monofilament test. Rapid rectal balloon distention measuring visceral sensitivity and evoked potentials was performed as a proxy for gut autonomic nerve function. The COMPASS 31 questionnaire was distributed and answered online. Results: Both groups of diabetes were hyposensitive to first sensation performing rapid rectal balloon distention. Also, those with reduced sensation performing the monofilament test showed hyposensitivity. A correlation was found between rectal hyposensitivity at the first sensation and reduced GIGD, but not with the incretin effect. Both GIGD and the incretin effect were found to correlate with degree of dysglycaemia and duration of diabetes, and were comparable to previous studies. Overall, few cases of confirmed neuropathy were detected, and there were few differences between groups regarding established neuropathy tests. Longer evoked potential latencies and smaller amplitudes plausibly correlated with lower heart rate variability and cardiovascular reflex test score, reduced parameters in the sural nerve test and monofilament sensation, but not statistically significant considering multiple testing. Higher scores in COMPASS 31 were correlated with longstanding diabetes and female sex. We found an acceptable negative predictive value for cardiovascular autonomic neuropathy at a 10-point cut-off . Conclusions: Rectal hyposensitivity may be an early manifestation of type 2 diabetes, and associated with GIGD, but not with the incretin effect. GIGD and the incretin effect are associated with degree of dysglycemia and duration of diabetes, indicating a continuum in the diminished effect. Central neuronal signal processing appears to be affected in parallel with peripheral neuronal function, but the results must be interpreted with caution. In general, we found that investigating evoked potentials following rapid rectal balloon distention may be a useful research tool for evaluating gut autonomic neuropathy, also when other autonomic neuropathy tests are normal. The Norwegian version of COMPASS 31 was easy to use and for assessing autonomic neuropathy in diabetes, and we suggest a cut off at ten points for screening purposes. Symptoms of autonomic neuropathy seems to be more frequent in people with longstanding diabetes and in women.Doktorgradsavhandlin

Refined electrophysiological recording and processing of neural signals from the retina and ascending visual pathways

The purpose of this thesis was the development of refined methods for recording and processing of neural signals of the retina and ascending visual pathways. The first chapter describes briefly the fundamentals of the human visual system and the basics of the functional testing of the retina and the visual pathways. The second and third chapters are dedicated to the processing of visual electrophysiological data using the newly developed software ERG Explorer, and present a proposal for an open and standardized data format, ElVisML, for future proof storage of visual electrophysiological data. The fourth chapter describes the development and application of two novel electrodes: First a contact lens electrode for the recording of electrical potentials of the ciliary muscle during accommodation, and second, the marble electrode, which is made of a super-absorbant polymer and allows for a preparation-free recording of visual evoked potentials. Results obtained in studies using the both electrodes are presented. The fifths and last chapter of the thesis presents the results from four studies within the field of visual electrophysiology. The first study examines the ophthalmological assessment of cannabis-induced perception disorder using electrophysiological methods. The second study presents a refined method for the objective assessment of the visual acuity using visual evoked potentials and introduces therefore, a refined stimulus paradigm and a novel method for the analysis of the sweep VEP. The third study presents the results of a newly developed stimulus design for full-field electrophysiology, which allows to assess previously non-recordable electroretinograms. The last study describes a relation of the spatial frequency of a visual stimulus to the amplitudes of visual evoked potentials in comparison to the BOLD response obtained using functional near-infrared spectroscopy and functional magnetic resonance imaging