Hybrid Brain-Computer Interface Systems: Approaches, Features, and Trends

Brain-computer interface (BCI) is an emerging field, and an increasing number of BCI research projects are being carried globally to interface computer with human using EEG for useful operations in both healthy and locked persons. Although several methods have been used to enhance the BCI performance in terms of signal processing, noise reduction, accuracy, information transfer rate, and user acceptability, the effective BCI system is still in the verge of development. So far, various modifications on single BCI systems as well as hybrid are done and the hybrid BCIs have shown increased but insufficient performance. Therefore, more efficient hybrid BCI models are still under the investigation by different research groups. In this review chapter, single BCI systems are briefly discussed and more detail discussions on hybrid BCIs, their modifications, operations, and performances with comparisons in terms of signal processing approaches, applications, limitations, and future scopes are presented

Neurofeedback Therapy for Enhancing Visual Attention: State-of-the-Art and Challenges

We have witnessed a rapid development of brain-computer interfaces (BCIs) linking the brain to external devices. BCIs can be utilized to treat neurological conditions and even to augment brain functions. BCIs offer a promising treatment for mental disorders, including disorders of attention. Here we review the current state of the art and challenges of attention-based BCIs, with a focus on visual attention. Attention-based BCIs utilize electroencephalograms (EEGs) or other recording techniques to generate neurofeedback, which patients use to improve their attention, a complex cognitive function. Although progress has been made in the studies of neural mechanisms of attention, extraction of attention-related neural signals needed for BCI operations is a difficult problem. To attain good BCI performance, it is important to select the features of neural activity that represent attentional signals. BCI decoding of attention-related activity may be hindered by the presence of different neural signals. Therefore, BCI accuracy can be improved by signal processing algorithms that dissociate signals of interest from irrelevant activities. Notwithstanding recent progress, optimal processing of attentional neural signals remains a fundamental challenge for the development of efficient therapies for disorders of attention

Electrophysiology

The outstanding evolution of recording techniques paved the way for better understanding of electrophysiological phenomena within the human organs, including the cardiovascular, ophthalmologic and neural systems. In the field of cardiac electrophysiology, the development of more and more sophisticated recording and mapping techniques made it possible to elucidate the mechanism of various cardiac arrhythmias. This has even led to the evolution of techniques to ablate and cure most complex cardiac arrhythmias. Nevertheless, there is still a long way ahead and this book can be considered a valuable addition to the current knowledge in subjects related to bioelectricity from plants to the human heart

TOWARDS STEADY-STATE VISUALLY EVOKED POTENTIALS BRAIN-COMPUTER INTERFACES FOR VIRTUAL REALITY ENVIRONMENTS EXPLICIT AND IMPLICIT INTERACTION

In the last two decades, Brain-Computer Interfaces (BCIs) have been investigated mainly for the purpose of implementing assistive technologies able to provide new channels for communication and control for people with severe disabilities. Nevertheless, more recently, thanks to technical and scientific advances in the different research fields involved, BCIs are gaining greater attention also for their adoption by healthy users, as new interaction devices. This thesis is dedicated to to the latter goal and in particular will deal with BCIs based on the Steady State Visual Evoked Potential (SSVEP), which in previous works demonstrated to be one of the most flexible and reliable approaches. SSVEP based BCIs could find applications in different contexts, but one which is particularly interesting for healthy users, is their adoption as new interaction devices for Virtual Reality (VR) environments and Computer Games. Although being investigated since several years, BCIs still poses several limitations in terms of speed, reliability and usability with respect to ordinary interaction devices. Despite of this, they may provide additional, more direct and intuitive, explicit interaction modalities, as well as implicit interaction modalities otherwise impossible with ordinary devices. This thesis, after a comprehensive review of the different research fields being the basis of a BCI exploiting the SSVEP modality, present a state-of-the-art open source implementation using a mix of pre-existing and custom software tools. The proposed implementation, mainly aimed to the interaction with VR environments and Computer Games, has then been used to perform several experiments which are hereby described as well. Initially performed experiments aim to stress the validity of the provided implementation, as well as to show its usability with a commodity bio-signal acquisition device, orders of magnitude less expensive than commonly used ones, representing a step forward in the direction of practical BCIs for end users applications. The proposed implementation, thanks to its flexibility, is used also to perform novel experiments aimed to investigate the exploitation of stereoscopic displays to overcome a known limitation of ordinary displays in the context of SSVEP based BCIs. Eventually, novel experiments are presented investigating the use of the SSVEP modality to provide also implicit interaction. In this context, a first proof of concept Passive BCI based on the SSVEP response is presented and demonstrated to provide information exploitable for prospective applications

BCIs and mobile robots for neurological rehabilitation: practical applications of remote control. Remote control of mobile robots applied in non-invasive BCI for disabled users afflicted by motor neurons diseases

This project aims at testing the possible advantages of introducing a mobile robot as a physical input/output device in a Brain Computer Interface (BCI) system. In the proposed system, the actions triggered by the subject’s brain activity results in the motions of a physical device in the real world, and not only in a modification of a graphical interface. A goal-based system for destination detecting and the high entertainment level offered by controlling a mobile robot are hence main features for actually increase patients' life quality leve

Photogenetic Retinal Prosthesis

The last few decades have witnessed an immense effort to develop working retinal implants for patients suffering from retinal degeneration diseases such as retinitis pigmentosa. However, it is becoming apparent that this approach is unable to restore levels of vision that will be sufficient to offer significant improvement in the quality of life of patients. Herein, a new type of retinal prosthesis that is based on genetic expression of microbial light sensitive ion channel, Chanelrhodopsin-2 (ChR2), and a remote light stimulation is examined. First, the dynamics of the ChR2 stimulation is characterized and it is shown that (1) the temporal resolution of ChR2-evoked spiking is limited by a continuous drop in its depolarization efficiency that is due to (a) frequency-independent desensitization process and (b) slow photocurrent shutting, which leads to a frequency-dependent post-spike depolarization and (2) the ChR2 response to light can be accurately reproduced by a four-state model consisting of two interconnected branches of open and close states. Then, a stimulation prototype is developed and its functionality is demonstrated in-vitro. The prototype uses a new micro-emissive matrix which enables generating of two-dimensional stimulation patterns with enhanced resolution compared to the conventional retinal implants. Finally, based on the micro-emitters matrix, a new technique for sub-cellular and network-level neuroscience experimentations is shown. The capacity to excite sub-cellular compartments is demonstrated and an example utility to fast map variability in dendrites conductance is shown. The outcomes of this thesis present an outline and a first proof-of-concept for a future photogenetic retinal prosthesis. In addition, they provide the emerging optogenetic technology with a detailed analysis of its temporal resolution and a tool to expand its spatial resolution, which can have immediate high impact applications in modulating the activity of sub-cellular compartments, mapping neuronal networks and studying synchrony and plasticity effects

DESIGN OF PORTABLE LED VISUAL STIMULUS AND SSVEP ANALYSIS FOR VISUAL FATIGUE REDUCTION AND IMPROVED ACCURACY

Brain-computer interface (BCI) applications have emerged as an innovative communication channel between computers and human brain as it circumvents peripheral limbs thereby creating a direct interface between brain thoughts and the external world. This research focuses on non-invasive BCI to improve the design of visual stimuli in eliciting steady-state visual evoked potential (SSVEP) for BCI applications. To evoke SSVEP in the brain, the user needs to focus on a visual stimulus flickering at a constant frequency. Traditionally in research studies, the visual stimulus for SSVEP uses LCD screens where the flicker is generated using black or white patterns, which alternates the colour to produce a flickering effect. However, there are drawbacks for LCD based visual stimuli systems that limit the user acceptance of SSVEP applications. The main limitations are: (i) choice of flicker frequency is limited to the LCDs vertical refresh rate (ii) flickers are mainly limited to black/white patterns (iii) higher visual fatigue for the user due to LCDs background flicker (iv) reduced visual stimulus portability (v) Inaccurate flickers generated and controlled by the software (vi) influence of adjacent flickers causing attention shift when multiple flickers are used for classification and also not being easily adaptable for user requirements. The impediments in eliciting and utilising SSVEP responses for designing a near real-time platform for controlling external applications are addressed from five main perspectives here: (i) design of standalone LED visual stimulus hardware for precise generation of any frequency for replacing the LCD based visual stimulus (ii) eliciting maximal response by choosing most responsive colour, orientation and shape of visual stimulus (iii) identification of the best luminance level for visual stimulus to improve the comfortability of the user and for improved SSVEP response (iv) control of the duration of ON/OFF period for the visual stimulus to reduce eyestrain for the user (i.e. visual fatigue), and (v) hybrid BCI paradigm using SSVEP and P300 to improve the classification accuracy for controlling external applications. The experimental study involved the development of various visual stimulus designs based on LEDs and microcontrollers to minimise the visual fatigue and improve the SSVEP responses. The signal analysis results from the studies with five to ten participants show SSVEP elicitation is influenced by colour, orientation, the shape of stimulus, the luminance level of stimulus and the duration of ON/OFF period for the stimulus. The participants also commented that choosing the correct luminance and ON/OFF periods of the stimulus considerably reduce the eyestrain, improve the attention levels and reduce the visual fatigue. Taken together, these finding leads to more user acceptance in SSVEP based BCI as an assistive mechanism for controlling external applications with improved comfort, portability and reduced visual fatigue

High density microelectrode arrays for in vitro retinal studies

Neurophysiologists traditionally studied the behaviour of individual neurons by measuring their extracellular signalling on a single electrode. This PhD has involved developing a technology to enable the behaviour of populations of neurons in the retina to be studied. By recording simultaneously from hundreds of neurons a much greater insight into retinal processing and encoding is achievable. To this end, a large area, high density, transparent microelectrode array, of unprecedented dimensions, was manufactured on a glass/indium tin oxide (ITO) substrate. This state-of-the-art device has 519 hexagonally close-packed, 5 mum diameter electrodes spaced by 30 mum. Al-1 channels are electrically well isolated with typical interchannel resistance and capacitance values of ~200 GO and 1 pF respectively. Electrodes are electroplated with platinum to form a low impedance (200 kO at 1 kHz) interface between the electrodes and electrolyte. Fabrication and modelling tests also proved the electrical and physical feasibility of future larger area and higher density arrays. Investigations were carried out to establish an electrode/electrolyte interface capable of delivering enough charge to directly stimulate neurons in the retina. Iridium oxide films formed by an electrochemical activation technique were found to create 5 mum diameter electrodes with 4 mC/cm2 charge capacity and 150 kO (at 1 kHz) impedance which are ideal characteristics for direct electrical stimulation of neurons. The state-of-the-art microelectrode array technology developed in this thesis has allowed amongst the most complete datasets from primate retina to be produced

Neuromechanical measurement of motor impairments in relation to upper limb activity limitations after stroke

Loss of upper-limb function is a problem following stroke. Recent research has led to the emergence of new treatments but progress is hampered by lack of reliable objective measures of impairment, and understanding of the underlying impairment mechanisms associated with loss and recovery of functional activity. The aim of this research was to identify, using neuromechanical measurement methods, inter-relationships between motor impairments, and correlates of motor impairments with functional activity limitation in the upper limb of acute and chronic stroke survivors.An instrumented rig has been developed to measure impairments: muscle weakness, active range of movement, motor control accuracy in rhythmic and discrete tracking tasks, spasticity, coactivation, contracture and non-neural stiffness. In pilot studies, signal processing and data analysis techniques have been used to generate novel, clinically and physiologically relevant indices to quantify impairments. In a Main Study, 13 older impaired participants in the acute phase post-stroke, 13 in the chronic phase 14 age-matched unimpaired participants underwent rig assessments and performed a test of upper limb activity. A sub-group of impaired participants were tested on two days for test-retest reliability evaluation.Statistical tests have confirmed the validity of the impairments to distinguish between acute and chronic patients and unimpaired individuals, except coactivation during discrete movements and non-neural stiffness. Repeatability coefficients for the active test indices have been presented as benchmark values for use in future trials. The muscle activation indices showed lower repeatability which highlights the challenge of using these to measure change over time. The impairments that contributed to lower motor control accuracy were reduced extensor weakness, delayed extensor onset timing, coactivation and smaller extension AROM and PROM; coactivation was more strongly associated with motor control accuracy than with spasticity or stiffness.The most important contributors to functional activity in the acute group was extensor weakness, and in the chronic group was motor control accuracy and coactivation (rhythmic task). Contracture was important contributor in both groups, and was associated with weakness and loss of active range of movement rather than spasticity. The findings support the notion that rehabilitation strategies should focus on increasing muscle strength and prevention of contracture. However, assessment of more complex impairments like motor control accuracy and coactivation may be crucial to better target therapy, especially in the later phases post-stroke