Dissertations / Theses on the topic 'Onde cerebrali'

La schizofrenia è una psicopatologia caratterizzata da sintomi psicotici prominenti. Sebbene dopo oltre 100 anni di ricerche le cause della malattia risultino ancora sconosciute, alcune recenti teorie hanno evidenziato il possibile ruolo di una sindrome di disconnessone e/o di un disturbo nella coordinazione dinamica. Pertanto, i meccanismi che mediano la generazione di attività coerenti e coordinate nei circuiti corticali sono fra i principali candidati per comprendere la psicosi in esame. Le oscillazioni neurali sono un meccanismo fondamentale per permettere il coordinamento delle attività durante il normale funzionamento cerebrale e sono perciò un punto fondamentale su cui si basano le attuali ricerche sulla schizofrenia. Questo elaborato ha l’obiettivo di evidenziare il ruolo che alterazioni delle oscillazioni neurali possono rivestire nella genesi della schizofrenia, tramite la revisione delle evidenze provenienti da diversi studi (tra cui il recente di Adams, pubblicato nell’aprile 2020) e di esaminare, inoltre, le possibili cause neurobiologiche delle onde neurali anomale, quali deficit nell’attività degli interneuroni GABAergici.

Questo lavoro ha riguardato lo studio del ritmo alpha nei segnali elettroencefalografici (EEG) in due condizioni: occhi chiusi e occhi aperti. I segnali EEG (relativi a 16 elettrodi distribuiti su tutto lo scalpo) sono stati tratti da un dataset disponibile online, e riguardano 20 soggetti sani a cui, nel corso della registrazione, veniva chiesto alternativamente di chiudere e di aprire gli occhi mantenendo la condizione per 10 secondi. L’elaborazione dei segnali EEG è consistita in un filtraggio passa-banda e nella successiva estrazione delle epoche ad occhi chiusi e ad occhi aperti; quindi, è stata stimata la densità spettrale di potenza di ciascun canale separatamente nelle epoche ad occhi chiusi e ad occhi aperti, per evidenziare la differenza nel contenuto frequenziale tra le due condizioni. Per determinare con maggiore precisione la potenza in banda alpha per ciascun soggetto, si è tenuto conto della variabilità interindividuale, identificando per ogni soggetto la Individual Alpha-band Window (IAW), ovvero il proprio intervallo individuale di frequenze alpha. La IAW è stata determinata usando un algoritmo già esistente, sfruttando lo spettro di potenza ad occhi chiusi, nel quale il ritmo alpha è più marcato. Ѐ stata quindi calcolata la potenza in banda alpha (nella IAW) di ciascun soggetto per ciascun elettrodo, evidenziando le differenze tra le due condizioni, con la potenza ad occhi chiusi nettamente superiore, e valori di potenza maggiori negli elettrodi posteriori. Le successive analisi hanno riguardato la valutazione di una possibile relazione tra la potenza in banda alpha (nei canali posteriori ad occhi chiusi) e le caratteristiche dei soggetti: il genere, l’età e il livello di stress dichiarato. Infine, è stata confrontata la potenza in banda alpha tra i due emisferi. I risultati mostrano un generale accordo con la letteratura. Il lavoro svolto ha consentito di approcciare elaborazioni e problematiche di analisi proprie dei segnali biomedici reali.

Il presente lavoro indaga i meccanismi di predizione e di sincronizzazione neurale nei bambini, sulla base dell’ipotesi che questi possano essere elementi rilevanti nei processi di elaborazione ritmica e morfosintattica. Sia il metro ritmico che il linguaggio sono organizzati in strutture gerarchiche in cui gli elementi sono ordinati secondo regole specifiche (Fitch & Martins, 2014). La conoscenza di queste regole porta alla formazione automatica di aspettative riguardo al materiale in arrivo; queste aspettative sono ritenute fondamentali per l'elaborazione efficiente del linguaggio e del ritmo, così anche come per la lettura (Guasti et al., 2017). In questa tesi abbiamo ipotizzato che migliori capacità di elaborazione gerarchica nel ritmo possano portare a migliori capacità di processamento di strutture gerarchiche nel linguaggio e che deficit in queste abilità possano portare allo sviluppo di disturbi del linguaggio e/o della lettura. Per valutare se le abilità nel fare previsioni strutturali correlino tra ritmo e il linguaggio, abbiamo studiato e confrontato le capacità di predire materiale linguistico (sulla base di informazioni morfosintattiche) e materiale ritmico in gruppi di bambini a sviluppo tipico (in inglese, TD) con o senza formazione musicale e in partecipanti con dislessia evolutiva (in inglese, DD). I risultati hanno confermato le nostre ipotesi, in quanto hanno mostrato predizioni strutturali migliori nei musicisti rispetto ai non-musicisti nel gruppo dei tipici e migliori predizioni strutturali nei TD rispetto ai bambini con dislessia. Inoltre, i risultati suggeriscono miglioramenti nell’efficienza delle strategie di processamento con l’aumentare dell’età. In secondo luogo, abbiamo ipotizzato che differenze individuali nella forza e nella efficienza con cui si fanno predizioni temporali e di contenuto possano dipendere da differenze individuali nell’efficienza e nella precisione dei meccanismi neurali di sincronizzazione delle oscillazioni cerebrali rispetto agli stimoli uditivi. Per testare queste ipotesi, abbiamo analizzato le risposte neurali di bambini TD e di bambini affetti da disturbo evolutivo del linguaggio (in inglese, DLD) in un paradigma sperimentale progettato per suscitare diverse interpretazioni metriche (e quindi gerarchiche). I risultati hanno mostrato che tutti i bambini erano sensibili alle caratteristiche metriche degli stimoli e che le differenze individuali nell’attività neurale predicevano le prestazioni in compiti sintattici. Inoltre, i risultati hanno suggerito che i bambini con DLD potrebbero avere attività oscillatoria atipica nella banda di frequenza gamma (che, secondo gli studi in letteratura (p.es., Ding et al., 2017), è importante per l’elaborazione gerarchica). In accordo con Ladányi, Persici, et al. (in revisione), sosteniamo che l’attività oscillatoria a livello neurale possa svolgere un ruolo chiave nel supportare il processamento degli elementi di base e delle strutture gerarchiche, sia nel ritmo che nel linguaggio, e che questo supporto passi attraverso il miglioramento delle predizioni strutturali. Sosteniamo, quindi, che migliori capacità di sincronizzazione neurale si traducano in migliori capacità di predizione strutturale e che queste, a loro volta, possano influenzare positivamente l’elaborazione ritmica e linguistica. Le evidenze presentate in questo lavoro rimarcano l’importanza dello studio dell’attività oscillatoria cerebrale nei bambini piccoli e suggeriscono la possibilità di utilizzare questi paradigmi nell’infanzia per poter predire il futuro sviluppo di disturbi del linguaggio e/o della lettura. Inoltre, gli studi qui riportati sottolineano come la formazione musicale sia importante per il miglioramento dei processi di elaborazione linguistica e suggeriscono che l’uso di attività ritmiche, in particolare, possa giocare un ruolo fondamentale nel trattamento dei disturbi del linguaggio e della lettura.
This work investigates prediction mechanisms and neural entrainment in children as the possible elements underlying both rhythmic and morphosyntactic processing. Both rhythmic meter and language are organized in hierarchical structures in which elements are ordered following specific rules (Fitch and Martins, 2014). Knowledge of these rules triggers compulsive expectancies regarding incoming material; these are assumed to be fundamental for efficient language and rhythmic processing and for reading (Guasti et al., 2017; Grüter, Rohde and Schafer, 2014; Miyake, Onishi and Pöppel, 2004; Persici et al., 2019). In this work we hypothesized that better hierarchical processing abilities in rhythm may transfer to the language domain, and that deficits in hierarchical processing may lead to language and/or reading disorders. To test whether abilities in making structure-based predictions correlate across domains, we investigated the abilities to infer the arrival of morphosyntactic and rhythmic material in groups of children with typical language development (TD) with or without musical training, and in participants with Developmental Dyslexia (DD). Results confirmed our hypotheses, as they showed better structure-based predictions in musician children than in non-musician TD children, and in TD children than in DD children. Results also suggested that efficiency of processing strategies improves with age. Secondly, we hypothesized that individual differences in strength of timing and content structure-based predictions may be the result of individual differences in the efficiency and precision with which brain oscillations entrain to auditory stimuli (‘neural entrainment’). To address these hypotheses, we tested the neural responses of TD children and of children with Developmental Language Disorder (DLD) in an experimental paradigm that was designed to elicit different metrical (hierarchical) interpretations. Results showed that all children were sensitive to hierarchical structures, and that individual differences in neural activity predicted individual differences in syntactic performance. Importantly, results also suggested that children with DLD might have atypical oscillatory activity in the gamma frequency band, which is important for hierarchical processing (Ding et al., 2017). In line with Fiveash et al. (submitted) and in Ladányi, Persici, et al. (submitted), we propose that neural oscillatory activity plays a key role in supporting the processing of both surface-level features and of syntactic structures in both musical rhythm and language, through an enhancement of structure-based prediction abilities; individual differences in neural entrainment will lead to individual differences in strength of predictions, which in turn will lead to individual differences in language and rhythm performance. The evidence presented in this work indicates that neural oscillatory activity gives an important insight into the language abilities of children and suggests that studying neural responses to rhythm in infancy may help predict the later development of language/reading disorders. Furthermore, our results suggest that musical training has positive effects on hierarchical processing, and that musical interventions centered on rhythm may enhance mechanisms of neural entrainment and timing, as well as hierarchical processing skills.

I nostri precedenti studi dimostrano che liposomi multifunzionalizzati con il monomero dell’ApoE e con acido fosfatidico (mApoE-PA-LIP) riducono l’accumulo di Aβ nel cervello migliorando il declino cognitivo in modelli murini di malattia di Alzheimer (AD) (Balducci et al., 2014). In riferimento ai nostri precedenti risultati, abbiamo studiato l’interazione di liposomi funzionalizzati con un peptide derivante dall’ApoE (mApoE) e acido fosfatidico (PA), con le cellule che costituiscono l’unità neurovascolare. In particolar modo, abbiamo valutato la loro attività in cellule di microcircolo cerebrale umano (hCMEC/D3), utilizzate come modello in vitro di barriera ematoencefalica, e in astrociti in coltura (iAstro-WT). Grazie a misurazioni effettuate con la tecnica del calcium imaging abbiamo studiato le dinamiche di calcio intracellulare generate dall’attivazione dei recettori purinergici. I nostri risultati mostrano che l’interazione dei mApoE-PA-LIP con le hCMEC/D3 e gli astrociti inducono attivamente una modulazione della durata delle onde di calcio indotte dall’attivazione dei recettori purinergici stimolati da ATP. In particolare, possiamo confermare che il pre-trattamento con i mApoE-PA-LIP induce un aumento significativo della durata della risposta indotta dall’ATP che non si verifica nelle cellule controllo. Dopo il pre-trattamento con mApoE-PA_LIP, anche l’area sotto la curva (AUC) risulta essere maggiore rispetto alle cellule non pre-trattate sia nelle hCMEC che negli iAstro-WT. Possiamo inoltre affermare che il pre-trattamento con i mApoE-PA-LIP in assenza di calcio extracellulare, aumenta in modo significativo sia i valori di durata di risposta al calcio allo stimolo di ATP sia quelli di AUC paragonati ai controlli. In aggiunta, abbiamo trovato che quando la pompa del calcio del reticolo sarcoplasmatico (SERCA) è inattiva, perché selettivamente bloccata dall’acido ciclopiazonico, in presenza o assenza di calcio extracellulare, l’ATP non riesce a generare onde di calcio anche dopo pre-trattamento con i mApoE-PA-LIP. In conclusione, considerando il ruolo neuroprottettivo dell’attivazione dei recettori purinergici (Weisman et al., 2012), possiamo affermare che i mApoE-PA-LIP modulano le dinamiche al calcio ATP indotte quando la SERCA è attiva. I nostri risultati potrebbero aggiungere dati interessanti utili a promuovere i mApoE-PA-LIP come innovativo strumento per il trattamento della malattia di Alzheimer.
Our previous results show that multifunctional liposomes (mApoE-PA-LIP) reduce brain Aβ burden and ameliorate memory impairment in Alzheimer’s disease (AD) mouse models (Balducci et al., 2014). In light of these results, we assessed liposomes functionalized with ApoE-derived peptide (mApoE) and phosphatidic acid (PA) at neurovascular unit. In particular, we evaluated their activities on cultured human cerebral microvascular cells (hCMEC/D3), as an in vitro human blood brain barrier model, and on cultured astrocytes (iAstro-WT). By means of calcium imaging measurements, we aimed to study the intracellular calcium dynamics triggered by purinergic receptors activation. Our result show that the interaction of mApoE-PA-LIP with the hCMEC/D3 and astrocytes actively induced a modulation in the calcium waves duration of ATP evoked response. In particular, we find an increase of the duration of the ATP evoked calcium waves in presence of mApoE-PA-LIP in comparison to untreated cells. After the mApoE-PA-LIP pre-treatment also the area under the curve (AUC) is increased in comparison to controls both in hCMEC and iAstro-WT. Furthermore, we found that the pre-treatment with mApoE-PA-LIP in absence of extracellular calcium significantly increased ATP evoked calcium waves in comparison to controls. Also under this condition, the AUC increased in comparison to control. We also found that when the Sarco-Endoplasmic Reticulum Calcium ATPase (SERCA) was inactive, due to its specific blockage with cyclopiazonic acid, both in presence or in absence of extracellular calcium, ATP failed to activate calcium wave also after a pre-treatment with mApoE-PA-LIP both in hCMEC and iAstro-WT. In conclusion, mApoE-PA-LIP modulate calcium dynamics evoked by ATP when SERCA is active. In light of the protective role of the purinergic receptor activation (Weisman et al., 2012), our obtained results would provide an additional support to promote mApoE-PA-LIP as putative therapeutic tool for AD treatment.

Eficacia de las ondas de choque radiales en comparación con la toxina botulínica tipo A en el tratamiento de la espasticidad de las extremidades inferiores en pacientes con parálisis cerebral: Ensayo clínico cruzado y aleatorizado. Antecedentes: La espasticidad es un trastorno motor que afecta a la musculatura de las extremidades inferiores en el 75% de los pacientes con parálisis cerebral (PC), afectando significativamente en su movilidad y calidad de vida. Hay mucha controversia sobre cuál es el tratamiento más adecuado de la espasticidad en estos pacientes, pero la Toxina Botulínica A (TBA) sigue siendo el tratamiento de elección. En la actualidad hay pocos estudios aunque esperanzadores sobre el tratamiento de la espasticidad mediante la aplicación con ondas de choque (rESWT). Hipótesis: La eficacia de las ondas de choque para el tratamiento de la espasticidad en la musculatura flexora plantar en pacientes con parálisis cerebral, no es inferior a la de la toxina botulínica. Objetivos: Evaluar los efectos de la terapia con ondas de choque radiales (rESWT) en comparación con el tratamiento con toxina botulínica (TBA) para mejorar la espasticidad en pacientes con parálisis cerebral. Métodos: Ensayo clínico aleatorizado y cruzado con cegamiento del evaluador. Se aleatorizaron 70 pacientes con parálisis cerebral de forma centralizada. El grupo de ondas de choque (rESWT) recibió una sesión por / semana durante 3 semanas. El grupo de toxina botulínica (TBA) recibió una sola sesión mediante infiltración en la musculatura flexora plantar. Todos los pacientes se sometieron a ambas terapias dejando un período de lavado de tres meses entre ambas. La variable principal fue la espasticidad, medida a partir del rango de movimiento pasivo de la musculatura flexora plantar y de su reflejo de estiramiento (mediante goniometría). Se evaluó al inicio del estudio, así como después de 3 semanas, 2 meses, 3 meses, después del periodo de lavado de 3 meses, a los 6 meses y 3 semanas, 8 meses y 9 meses. Las variables secundarias fueron el dolor evaluado mediante la escala visual analógica (EVA) después de la primera aplicación de cada terapia, determinar si el nivel de Gross Motor Functional Glassification System (GMFCS) influye en la mejora de estos dos tratamientos, evaluar si influye en los resultados el hecho de haber sido infiltrado en otros músculos a parte de la musculatura flexora plantar, realizar un registro cualitativo para conocer la percepción y la experiencia que el paciente / familia ha tenido durante este estudio, y finalmente registrar los posibles efectos adversos aparecidos tras la aplicación de una u otra terapia. La eficacia se analizó con intención de tratar y por protocolo (PP). Los efectos de la intervención sobre los parámetros de goniometría fueron evaluados con modelos lineales generales. El efecto de la intervención sobre el dolor se midió con test de t de muestras pareadas y los datos cualitativos se analizaron en un proceso metódico utilizando la técnica de análisis de contenido temático. Resultados: Todos los pacientes tratados con ondas de choque mejoraron tanto en la extensibilidad muscular como en los reflejos de estiramiento de los músculos sóleo y gastrocnemio con unos efectos mejores que los de la toxina (p<0.005) manteniendo su efecto hasta los 3 meses. En ningún caso hubo efecto secuencia lo que corrobora la buena elección del diseño de estudio. En relación a las otras variables clínicas analizadas, los resultados muestran diferencias estadísticamente significativas para: 1) la variable dolor entre las dos intervenciones p<0.001 donde los participantes mostraron mejor tolerancia y una mejor vivencia con la terapia mediante ondas de choque, 2) la variable influencia del nivel de GMFCS, los resultados muestran diferencias estadísticamente significativas entre los participantes y todos obtuvieron resultados positivos independientemente del nivel motor p<0.005; 3) en relación a la variable influencia de haber recibido infiltraciones con TBA en otros músculos, no se observaron diferencias significativas entre ambos grupos. Por último, en relación a la variable efectos adversos, los resultados muestran que no aparecieron efectos adversos importantes más que un ligero hematoma en un participante en el caso de la intervención mediante rESWT y debilidad muscular en dos participantes mediante las infiltraciones con TBA. Conclusión: Este estudio muestra que las ondas de choque radiales rESWT son eficaces para el tratamiento de la espasticidad en pacientes con parálisis cerebral. Así pues las ondas de choque pueden ser una buena alternativa a la toxina botulínica. Este es el primer estudio que compara ambas técnicas aunque son necesarios futuros estudios que evalúen los efectos a largo plazo para corroborar la eficacia y la seguridad de esta intervención. Palabras clave: Parálisis cerebral; Toxina botulínica; Onda de choque; Espasticidad; Fisioterapia.

This is a qualitative study of one student’s use of assistive technology in the public school system from preschool to fourth grade. The data collected for this case study include interviews, participant observation, field and diary notes, video tapes, and other documents including school records and a teacher memoir. Throughout the study, the goals were to stay open to and reflect emerging patterns rather than to fit data into previously determined categories. The report describes how Michael--with cerebral palsy that affects his speech and prevents his standing or holding a pencil--used computers, augmentative communication devices, and other electronic technology. On one level the report becomes the story of a student who moves from a separate special education facility into an elementary school where he is integrated fulltime into a fourth grade class. Discussion and conclusions explore (1) types of support he required, (2) barriers to technology use as well as problems of "abandonment" of technology acquired, (3) the effect of integration into general education on his use of technology, and (4) how providing assistive technology influences and changes teachers’ roles.
Ed. D.

Objectives: To study the effect of alpha neurofeedback training in anxiety and depression and its repercussion on reactivity and recovery from stress. Method: 14 participants (37.85 mean age) with stress, anxiety and/or depression, randomly assigned to intervention (N=7) and waiting list control groups (N=7). Procediment involved ten 30 minuts sessions of training. Mesures: Hospital Anxiety and Depression Scale and Brief Symptom Checklist; and the register of alpha wave amplitude and heart rate in three phases (Basal, Reactivity and Recovery) in the pre and post-test. Results: A reduction of anxiety, depression and psychosomatic symptoms after training. Alpha wave amplitude increased and heart rate decreased in reactivity and recovery phases after training. Conclusions: The training produces a reduction of the clinical variables and a positive effect on reactivity and recovery from stress.
Objetivos. Estudiar el efecto del entrenamiento en neurofeedback de onda alfa en la ansiedad y depresión y su repercusión en la reactividad y recuperación del estrés. Método: 14 participantes (edad media de 37.85 años) con estrés, ansiedad y/o depresión; asignadas aleatoriamente a grupos experimental (N=7) y control de lista de espera (N=7). El procedimiento implicó 10 sesiones de 30 minutos de entrenamiento. Medidas: Hospital Anxiety and Depression Scale y Listado de Síntomas Breve; y registro de amplitud de onda alfa y frecuencia cardíaca en tres fases (Basal, Reactividad y Recuperación) en el pre y post-test. Resultados: Reducción de ansiedad, depresión y síntomas psicosomáticos después del entrenamiento. La amplitud de onda alfa incrementó y la frecuencia cardíaca disminuyó en las fases de reactividad y recuperación después del entrenamiento. Conclusiones: El entrenamiento produce una reducción de las variables clínicas y un efecto positivo en la reactividad y recuperación del estrés.

Background: Little research has been conducted to date on the effective uptake of assistive technology for students with cerebral palsy. Available research indicates that these students experience considerable challenges (Copley & Ziviani, 2004, 2007; McMillan, 2008; Raghavendra, Olsson, Sampson, McInerney, & Connell, 2012). With clientcentred and family-centred care widely recognised as a cornerstone for effective assistive technology service provision (Angelo, 2000; Parette & Brotherson, 2004), the current study was undertaken to investigate to what extent such approaches were used by schools when assistive technology assessments and implementation occurred in the classroom. Furthermore, the factors determining the students’ capability to access the curriculum to achieve classroom goals were examined. In exploring these issues, this study is the first in Australia to investigate the service provision of high-tech assistive technology in schools for students with cerebral palsy. Methods: This two-phase sequential explanatory mixed methods study was designed to survey and interview all key stakeholders in the assistive technology provision process, in a multiple-case study design. The International Classification of Functioning, Disability and Health (ICF) (World Health Organization, 2001) for Children and Youth (ICF-CY) (World Health Organization, 2007) was used as a framework to describe the facilitators and barriers in assistive technology provision in the classroom. A cross-sectional survey of: parents (n=76), students aged 7-18 years (n=22), occupational therapists (n=33), speech pathologists (n=32), assistive technology consultants (n=4), educators (n=26) and teaching assistants (n=5) was conducted to investigate their experiences of assistive technology service provision and the students’ ability to access the curriculum. Furthermore, to evaluate how client-centred and family-centred the service provision was perceived to be, parents completed the Measure of Processes of Care for Caregivers (MPOC-20) (King, King, & Rosenbaum, 2004). School staff and allied health professionals completed the Measure of Processes of Care for Service Providers (MPOC-SP) (Woodside, Rosenbaum, King, & King, 2001); and youth aged 13 years and older completed the Give Youth a Voice (GYV-20). Descriptive and non-parametric statistics were used for data analysis of the survey. Based on the results obtained, semi-structured interviews and focus groups with parents (n=6), their children (n=6), educators (n=6) and allied health professionals (n=15) were conducted to further explore their experiences of service provision and use of assistive technology. These data were analysed using cross-case analysis. Results: This study found that family-centred service and shared decision-making is not yet fully achieved in schools despite being endorsed in early intervention and disability services for over 20 years. When students, their parents, the classroom teacher and a teaching assistant are involved alongside allied health professionals, in the process of selecting and implementing assistive technology in the classroom, successful outcomes are more likely to occur. However, the findings from this study show that classroom teachers are often not involved in the initial stages of the assessment process. For students to access the curriculum it is essential that both allied health professionals and school staff are clear about their roles and set goals with the students and their families. It is also critical for them to be open to learn new skills, have time to meet with other team members, and feel comfortable with implementing the technology. Students’ motivation and level of support and training from parents, school staff and allied health professionals played an integral part in the successful use of technology in the classroom. The study also demonstrated that ensuring adequate training and having a dedicated teaching assistant was perceived positively by parents, allied health professionals and school staff. Conclusion: These findings offer directions for service provision, policy development and future research. To increase access to the curriculum, client-centred and family-centred service provision needs to be fully embraced by schools. To enhance the way technology is matched to the student and successfully implemented, classroom teachers need to be fully involved in the whole assistive technology process. Clear policy guidelines on how to access technology equipment and funding are required. For students to be able to show teachers what they know, it is critical that they have someone encouraging them to use their technology in the classroom. These findings have the potential to better provide opportunities for students to access the curriculum and, in doing so, enable them to exercise their right to a meaningful education.

La tomografía de impedancia eléctrica (EIT) permite estimar la conductividad eléctrica interna de un cuerpo. Consiste en aplicar una corriente eléctrica sobre su frontera y medir el potencial eléctrico resultante mediante un arreglo de sensores. Es considerada como una potencial herramienta de diagnóstico médico, caracterizada principalmente por su portabilidad y relativo bajo costo. Si bien se encuentra aún en etapa de desarrollo, está comenzando a ser utilizada en centros de salud para la caracterización del aparato cardio-respiratorio y existe un creciente interés en su aplicación a las neurociencias. Por ejemplo, es posible utilizar la EIT para construir modelos virtuales de la cabeza más precisos mediante la estimación de la conductividad eléctrica de los principales tejidos de la cabeza como un conjunto de parámetros relativamente pequeño, modalidad denominada EIT paramétrico. También se puede utilizar la EIT para generar un mapa de la distribución de conductividad eléctrica interna de un objeto, llamado problema de reconstrucción en EIT. Los cambios de la conductividad eléctrica en la cabeza pueden estar asociados a la actividad neuronal, a focos epilépticos, a accidentes cerebro-vasculares o a tumores. Ambas modalidades de EIT requieren la resolución del problema directo (PD), que consiste en el cálculo de la distribución de potencial eléctrico en el objeto originada por la inyección de corriente sobre su superficie, suponiendo que la conductividad interna es conocida. La estimulación de corriente continua transcraneal (tDCS) es físicamente muy similar a la EIT, pero la corriente eléctrica es aplicada sobre el cuero cabelludo de modo de alterar la tasa de disparos de poblaciones de neuronas en una región de interés. Es una potencial alternativa al empleo de psicofármacos para tratar desórdenes como epilepsia o depresiones. En esta tesis se desarrollan y analizan nuevos métodos para distintos problemas de EIT, centrándose mayormente en aplicaciones a la cabeza humana, y de tDCS. En primer lugar, se describen soluciones analíticas y numéricas para el PD en EIT, estas últimas basadas en el método de los elementos finitos. Luego, se desarrolla un nuevo procedimiento para resolver el PD con bajo costo computacional basado en la formulación del PD en electroencefalografía (EEG). Se propone un nuevo método para determinar la forma de onda de la fuente de corriente que permite desafectar la actividad propia del cerebro con un bajo número de muestras temporales. En EIT paramétrico, se utiliza la cota de Cramér-Rao (CRB) para determinar pares de electrodos convenientes para la inyección de corriente y para analizar límites teóricos en la estimación de las conductividades del cráneo y del cuero cabelludo, modelizándolos como tejidos isótropos y anisótropos. A su vez, se propone el estimador de máxima verosimilitud (MLE) como herramienta para realizar las estimaciones. El MLE se aplica a mediciones simuladas y reales de EIT mostrando un desempeño muy cercano a los límites teóricos. Para el problema de reconstrucción en EIT se adapta el algoritmo sLORETA, muy utilizado en el problema de localización de fuentes de actividad neuronal en EEG. Además, se lo modifica levemente para incorporar la regularización espacial de Laplace. Por otro lado, se introduce la utilización de filtros espaciales adaptivos para localizar cambios de conductividad de pequeño tamaño y estimar su variación temporal. Los resultados muestran mejoras en sesgo y resolución, en comparación con algoritmos de reconstrucción típicos en EIT. Estas mejoras son potencialmente ventajosas en la detección de accidentes cerebro-vasculares y en la localización indirecta de fuentes de actividad neuronal. En tDCS, se desarrolla un nuevo algoritmo para la determinación de patrones de inyección de corriente basado en el principio de reciprocidad y que considera restricciones de seguridad y de hardware. Los resultados obtenidos a partir de simulaciones muestran que el desempeño de dicho algoritmo es comparable al desempeño de algoritmos de optimización tradicionales cuyas soluciones implicarían un equipamiento comparativamente más complejo y costoso. Los métodos desarrollados en la tesis son comparados con métodos pre-existentes y validados a través de simulaciones numéricas por computadora, mediciones sobre maquetas experimentales (ó fantomas) y, de acuerdo con las posibilidades experimentales y respetando los principios de la bioética, mediciones reales sobre humanos.
Electrical impedance tomography (EIT) is a technique to estimate the electrical conductivity of an object. It consists in the application of an electric current on its boundary and the measurement of the resulting electric potential with a sensor array. In clinical practise, it is considered as a potential diagnostic tool characterized by its portability and relatively low cost. While it is still in a development stage, it is starting to be used in health centers to characterize the cardio-respiratory system. In turn, there is an increasing interest of EIT in neuroscience. For example, EIT can be used to estimate the electrical conductivity of the main tissues of the head as a set of a relatively low number of parameters, which is known as bounded or parametric EIT. This is useful for several medical imaging techniques that require realistic and accurate virtual models of the head. EIT can also be used to generate a map of the internal distribution of the electrical conductivity, known as the reconstruction problem. Tracking conductivity changes inside the head is of great interest as they may be related to neuronal activity, epileptic foci, acute stroke, or tumors. Both modalities of EIT require the solution of the EIT forward problem (FP), i.e., the computation of the electric potential distribution due to current injection on the scalp assuming that the electrical conductivity is known. The transcranial direct current stimulation (tDCS) is another technique which is physically very similar to EIT. It consists in injecting a small electric current in a convenient way such that it stimulates specific neuronal populations, increasing or decreasing their firing rate. It is considered as an alternative to psychoactive drugs in the treatment of brain disorders such as epilepsy or depression. This thesis describes the development and analysis of new methods for EIT FP, parametric EIT, reconstruction in EIT, and tDCS, focusing primarily (although not exclusively) in applications to human head. We first describe analytical and numerical approaches for the EIT FP, where the numerical approach is based on the finite element method. Then, we develop a new procedure to solve the EIT FP based on the electroencephalography (EEG) FP formulation, which results in computational advantages. We propose a new method to determine the waveform of the electric current source such that the neuronal activity of the brain can be neglected with the smallest possible number of time samples. In parametric EIT, we use the Cramér-Rao bound (CRB) to determine convenient electrode pairs for the current injection and theoretical limits in the estimation of the electrical conductivity of the main tissues of the head, which we model as isotropic and anisotropic. We propose the maximum likelihood estimator (MLE) to estimate these conductivities and we test it with simulated and real EIT measurements, showing that the MLE performs close to the CRB. We adapt the sLORETA algorithm to the reconstruction problem in EIT. This algorithm is being widely used in the source localization problem in EEG. We also slightly modify it to include the Laplace smoothing prior in the solution. Likewise, we introduce the use of adaptive spatial filters in the localization of conductivity changes and the estimation of its time courses from EIT measurements. The results show improvements over typical EIT algorithms. These improvements may benefit the early detection of acute strokes and the localization of neuronal activity using EIT. In tDCS, we develop a new algorithm to determine convenient current injection patterns. It is based on the reciprocity principle and considers hardware and safety constraints. Our simulation results show that this method performs similarly to other commonly used algorithms that require more complex and costly equipments. The methods we develop and study in this thesis are compared with pre-existing methods and are validated through numerical simulations, measurements on phantoms and, according to the experimental possibilities and bioethical principles, humans.