An independent SSVEP-based brain-computer interface in locked-in syndrome.

OBJECTIVE: Steady-state visually evoked potential (SSVEP)-based brain-computer interfaces (BCIs) allow healthy subjects to communicate. However, their dependence on gaze control prevents their use with severely disabled patients. Gaze-independent SSVEP-BCIs have been designed but have shown a drop in accuracy and have not been tested in brain-injured patients. In the present paper, we propose a novel independent SSVEP-BCI based on covert attention with an improved classification rate. We study the influence of feature extraction algorithms and the number of harmonics. Finally, we test online communication on healthy volunteers and patients with locked-in syndrome (LIS). APPROACH: Twenty-four healthy subjects and six LIS patients participated in this study. An independent covert two-class SSVEP paradigm was used with a newly developed portable light emitting diode-based 'interlaced squares' stimulation pattern. MAIN RESULTS: Mean offline and online accuracies on healthy subjects were respectively 85 ± 2% and 74 ± 13%, with eight out of twelve subjects succeeding to communicate efficiently with 80 ± 9% accuracy. Two out of six LIS patients reached an offline accuracy above the chance level, illustrating a response to a command. One out of four LIS patients could communicate online. SIGNIFICANCE: We have demonstrated the feasibility of online communication with a covert SSVEP paradigm that is truly independent of all neuromuscular functions. The potential clinical use of the presented BCI system as a diagnostic (i.e., detecting command-following) and communication tool for severely brain-injured patients will need to be further explored.

Performance of a tactile P300 speller for healthy people and severely disabled patients.

P300 based Brain-Computer Interfaces (BCIs) for communication are well known since many years. Most of them use visual stimuli to elicit evoked potentials because it is easy to integrate a high number of different classes into the paradigm. Nevertheless, a BCI that depends on visual stimuli is sometimes not feasible due to the presence of visual impairment in patients with severe brain injuries. In this case, it could be possible to use auditory or somatosensory stimulation. In this publication a vibrotactile P300 based BCI is introduced. Two different approaches were tested: a first approach using two stimulators and a second one that utilizes three stimulators for emitting the stimuli. The two paradigms were tested on 16 users: A group of ten healthy users and a second group comprising of 6 patients suffering Locked-In Syndrome. The control accuracy was calculated for both groups and both approaches, proving the feasibility of the device, not only for healthy people but also in severely disabled patients. In a second step we evaluated the influence of the number of stimuli on the accuracy. It was shown that in many cases the maximum accuracy was already reached with a small number of stimuli, this could be used in future tests to speed up the Information transfer rate.

Electrophysiological investigations of brain function in coma, vegetative and minimally conscious patients.

Electroencephalographic activity in the context of disorders of consciousness is a swiss knife like tool that can evaluate different aspects of cognitive residual function, detect consciousness and provide a mean to communicate with the outside world without using muscular channels. Standard recordings in the neurological department offer a first global view of the electrogenesis of a patient and can spot abnormal epileptiform activity and therefore guide treatment. Although visual patterns have a prognosis value, they are not sufficient to provide a diagnosis between vegetative state/unresponsive wakefulness syndrome (VS/UWS) and minimally conscious state (MCS) patients. Quantitative electroencephalography (qEEG) processes the data and retrieves features, not visible on the raw traces, which can then be classified. Current results using qEEG show that MCS can be differentiated from VS/UWS patients at the group level. Event Related Potentials (ERP) are triggered by varying stimuli and reflect the time course of information processing related to the stimuli from low-level peripheral receptive structures to high-order associative cortices. It is hence possible to assess auditory, visual, or emotive pathways. Different stimuli elicit positive or negative components with different time signatures. The presence of these components when observed in passive paradigms is usually a sign of good prognosis but it cannot differentiate VS/UWS and MCS patients. Recently, researchers have developed active paradigms showing that the amplitude of the component is modulated when the subject's attention is focused on a task during stimulus presentation. Hence significant differences between ERPs of a patient in a passive compared to an active paradigm can be a proof of consciousness. An EEG-based brain-computer interface (BCI) can then be tested to provide the patient with a communication tool. BCIs have considerably improved the past two decades. However they are not easily adaptable to comatose patients as they can have visual or auditory impairments or different lesions affecting their EEG signal. Future progress will require large databases of resting state-EEG and ERPs experiment of patients of different etiologies. This will allow the identification of specific patterns related to the diagnostic of consciousness. Standardized procedures in the use of BCIs will also be needed to find the most suited technique for each individual patient.

Repercusión en los valores de Inmunoglobulinas en niños adenotonsilectomizados / Repercussion in the immunoglobulins values in children adenotonsillectomized

Se evaluaron 42 pacientes quienes consultaron al servicio de otorrinolaringología del Hospital de Niños "J. M. de Los Ríos" con criterios quirúrgicos de adenotonsilectomía, entre julio del 2000 a julio del 2001. Los datos se registraron en fichas de recolección de datos, las variables estudiadas fueron: edad, sexo, estudios pre y postquirúrgicos que incluyeron: inmunoglobulias serícas (Ig A, Ig G, Ig M e Ig E) inmunglobulina secretora (Ig As) y estudios preoperatorios de ASTO y exudado Faringeo. Los resultados presentan en gráficos tipo barra y circular. El método aplicado fue análisis estadístico de frecuencia. Las variaciones observadas en los valores de Igs, no fueron estadísticamente significativos, por lo cual la adenotonsilectomía no produce repercusión en la respuesta inmune.

Patología laríngea congénita en 96 niños / Congenital laryngeal pathology in ninety six childrens

Las anormalías Laríngeas Congénitas o Adquiridas se pueden presentar frecuentemente con Clínica de Estridor Laríngeo, Disfonía y Dificultad Respiratoria o Síntomas relacionados con la alimentación. En el Hospital de Niños "J. M. de Los Ríos" de Caracas, se estudiaron 553 pacientes con Patología Laríngea, de los cuales 96 casos presentaron Patología Laríngea Congénita; 227 casos, Patología Adquirida y 230 casos fueron considerados Laríngea Normal. De todos los pacientes con Patología Congénita el 67 por ciento (64 casos) Correspondían al sexo masculino y el 76 por ciento (73 casos) eran lactantes menores. El Estridor Laríngeo fue el motivo de Consulta predominante 81 por ciento (78 por ciento), seguido de Disfonía con el 14 por ciento (13) y el 3 por ciento (3) por Infecciones Respiratorias Recurrentes. La Patología Congénita que destacó fue la laringomalacia en 76 casos (78 por ciento); Quistes de Valléculas (6 por ciento), Hendidura Laríngea, Parálisis Unilateral de Cuerdas Vocales (4 por ciento) y Estenosis Subglótica Congénita. Todo paciente con síntomas laríngeos debe realizarsele evaluación endoscópica dinámica, para descartar Patologías asociadas y controlar la evolución del Cuadro Clínico. En la mayoría de los casos congénitos existe desaparición de la Patología en el tiempo, por lo tanto resulta fundamental esperar la madurez laríngea con el seguimiento y tratamiento médico de la integridad de mucosa más manejo de secreciones, para una exitosa recuperación, sin intercurrencias quirúrgicas.